CHAPTER XXVIII.

NECESSARY TRUTHS AND THE EFFECTS OF EXPERIENCE

Programme of the chapter. Elementary feelings are innate.

The question refers to their combinations. What is meant by

'experience'. Spencer on ancestral experience. Two ways

in which new cerebral structure arises: the 'back-door' and the

'front-door' way. The genesis of the elementary mental categories.

The genesis of the natural sciences. Scientific conceptions

arise as accidental variations. The genesis of the pure sciences.

Series of evenly increasing terms. The principle of mediate

comparison. That of skipped intermediaries. Classification.

Predication. Formal logic. Mathematical propositions.

Arithmetic. Geometry. Our doctrine is the same as

Locke's. Relations of ideas _v._ couplings of things The

natural sciences are inward ideal schemes with which the order of

nature proves congruent. Metaphysical principles are properly only

postulates. Æsthetic and moral principles are quite incongruent

with the order of nature. Summary of what precedes. The

origin of instincts. Insufficiency of proof for the transmission

to the next generation of acquired habits. Weismann's views.

Conclusion.

INDEX.

PSYCHOLOGY.

CHAPTER XVII.

SENSATION.

After inner perception, outer perception! The next three chapters will

treat of the processes by which we cognize at all times the present

world of space and the material things which it contains. And first, of

the process called Sensation.

SENSATION AND PERCEPTION DISTINGUISHED.

_The words Sensation and Perception_ do not carry very definitely

discriminated meanings in popular speech, and in Psychology also their

meanings run into each other. Both of them name processes in which we

cognize an objective world; both (under normal conditions) need the

stimulation of incoming nerves ere they can occur; Perception always

involves Sensation as a portion of itself; and Sensation in turn never

takes place in adult life without Perception also being there. They are

therefore names for different cognitive _functions_, not for different

sorts of mental _fact_. The nearer the object cognized comes to being a

simple quality like 'hot,' 'cold,' 'red,' 'noise,' 'pain,' apprehended

irrelatively to other things, the more the state of mind approaches

pure sensation. The fuller of relations the object is, on the contrary;

the more it is something classed, located, measured, compared, assigned

to a function, etc., etc.; the more unreservedly do we call the state

of mind a perception, and the relatively smaller is the part in it

which sensation plays.

_Sensation, then, so long as we take the analytic point of view,

differs from Perception only in the extreme simplicity of its object or

content._[1] Its function is that of mere _acquaintance_ with a fact.

Perception's function, on the other hand, is knowledge _about_[2] a

fact; and this knowledge admits of numberless degrees of complication.

But in both sensation and perception we perceive the fact as an

_immediately present outward reality_, and this makes them differ from

'thought' and 'conception,' whose objects do not appear present in this

immediate physical way. _From the physiological_ _point of view both

sensations and perceptions differ from 'thoughts'_ (in the narrower

sense of the word) _in the fact that nerve-currents coming in from

the periphery are involved in their production. In perception these

nerve-currents arouse voluminous associative or reproductive processes

in the cortex; but when sensation occurs alone, or with a minimum of

perception, the accompanying reproductive processes are at a minimum

too._

I shall in this chapter discuss some general questions more especially

relative to Sensation. In a later chapter perception will take its

turn. I shall entirely pass by the classification and natural history

of our special 'sensations,' such matters finding their proper place,

and being sufficiently well treated, in all the physiological books.[3]

THE COGNITIVE FUNCTION OF SENSATION.

_A pure sensation is an abstraction;_ and when we adults talk of our

'sensations' we mean one of two things: either certain _objects_,

namely simple _qualities_ or _attributes_ like _hard, hot, pain;_ or

else those of our thoughts in which acquaintance with these objects

is least combined with knowledge about the relations of them to other

things. As we can only think or talk about the relations of objects

with which we have _acquaintance_ already, we are forced to postulate

a function in our thought whereby we first become aware of the _bare

immediate natures_ by which our several objects are distinguished.

This function is sensation. And just as logicians always point out

the distinction between substantive terms of discourse and relations

found to obtain between them, so psychologists, as a rule, are ready to

admit this function, of the vision of the terms or matters meant, as

something distinct from the knowledge about them and of their relations

_inter se_. Thought with the former function is sensational, with the

latter, intellectual. Our earliest thoughts are almost exclusively

sensational. They merely give us a set of _thats_, or _its_, of

subjects of discourse, with their relations not brought out. The

first time we see _light_, in Condillac's phrase we _are_ it rather

rather than see it. But all our later optical knowledge is about what

this experience gives. And though we were struck blind from that first

moment, our scholarship in the subject would lack no essential feature

so long as our memory remained. In training-institutions for the blind

they teach the pupils as much _about_ light as in ordinary schools.

Reflection, refraction, the spectrum, the ether-theory, etc., are all

studied. But the best taught born-blind pupil of such an establishment

yet lacks a knowledge which the least instructed seeing baby has. They

can never show him what light is in its 'first intention'; and the loss

of that sensible knowledge no book-learning can replace. All this is so

obvious that we usually find sensation 'postulated' as an element of

experience, even by those philosophers who are least inclined to make

much of its importance, or to pay respect to the knowledge which it

brings.[4]

But the trouble is that most, if not all, of those who admit it,

admit it as a fractional _part_ of the thought, in the old-fashioned

atomistic sense which we have so often criticised.

Take the pain called toothache for example. Again and again we feel it

and greet it as the same real item in the universe. We must therefore,

it is supposed, have a distinct pocket for it in our mind into which it

and nothing else will fit. This pocket, when filled, is the sensation

of toothache; and must be either filled or half-filled whenever and

under whatever form toothache is present to our thought, and whether

much or little of the rest of the mind be filled at the same time.

Thereupon of course comes up the paradox and mystery: If the knowledge

of toothache be pent up in this separate mental pocket, how can it be

known _cum alio_ or brought into one view with anything else? This

pocket knows nothing else; no other part of the mind knows toothache.

The knowing of toothache _cum alio_ must be a miracle. And the miracle

must have an Agent. And the Agent must be a Subject or Ego 'out of

time,'--and all the rest of it, as we saw in Chapter X. And then begins

the well-worn round of recrimination between the sensationalists and

the spiritualists, from which we are saved by our determination from

the outset to accept the psychological point of view, and to admit

knowledge whether of simple toothaches or of philosophic systems as

an ultimate fact. There are realities and there are 'states of mind,'

and the latter know the former; and it is just as wonderful for a

state of mind to be a 'sensation' and know a simple pain as for it to

be a thought and know a system of related things.[5] But there is no

reason to suppose that when different states of mind know different

things about the same toothache, they do so by virtue of their all

_containing_ faintly or vividly the original pain. Quite the reverse.

The by-gone sensation of my gout was painful, as Reid somewhere says;

the _thought_ of the same gout as by-gone is pleasant, and in no

respect resembles the earlier mental state.

Sensations, then, first make us acquainted with innumerable things, and

then are replaced by thoughts which know the same things in altogether

other ways. And Locke's main doctrine remains eternally true, however

hazy some of his language may have been, that

"though there be a great number of considerations wherein things

may be compared one with another, and so a multitude of relations;

yet they all _terminate in_, and are concerned about, those simple

ideas[6] either of sensation or reflection, which I think to be the

whole materials of all our knowledge.... The simple ideas we receive

from sensation and reflection are the _boundaries_ of our thoughts;

beyond which, the mind whatever efforts it would make, is not able to

advance one jot; nor can it make any discoveries when it would pry

into the nature and hidden causes of those ideas."[7]

The nature and hidden causes of ideas will never be unravelled till

the _nexus_ between the brain and consciousness is cleared up. All

we can say now is that sensations are _first_ things in the way of

consciousness. Before conceptions can come, sensations must have

come; but before sensations come, no psychic fact need have existed,

a nerve-current is enough. If the nerve-current be not given, nothing

else will take its place. To quote the good Locke again:

"It is not in the power of the most exalted wit or enlarged

understanding, by any quickness or variety of thoughts, to invent or

frame one new simple idea [i.e. sensation] in the mind.... I would

have any one try to fancy any taste which had never affected his

palate, or frame the idea of a scent he had never smelt; and when

he can do this, I will also conclude that a blind man hath ideas of

colors, and a deaf man true distinct notions of sounds."[8]

The brain is so made that all currents in it run one way. Consciousness

of some sort goes with all the currents, but it is only when new

currents are entering that it has the sensational _tang_. And it is

only then that consciousness directly _encounters_ (to use a word of

Mr. Bradley's) a reality outside itself.

The difference between such encounter and all conceptual knowledge is

very great. A blind man may know all _about_ the sky's blueness, and

I may know all _about_ your toothache, conceptually; tracing their

causes from primeval chaos, and their consequences to the crack of

doom. But so long as he has not felt the blueness, nor I the toothache,

our knowledge, wide as it is, of these realities, will be hollow

and inadequate. Somebody must _feel_ blueness, somebody must _have_

toothache, to make human knowledge of these matters real. Conceptual

systems which neither began nor left off in sensations would be like

bridges without piers. Systems about fact must plunge themselves into

sensation as bridges plunge their piers into the rock. Sensations are

the stable rock, the _terminus a quo_ and the _terminus ad quem_ of

thought. To find such termini is our aim with all our theories--to

conceive first when and where a certain sensation may be had, and then

to have it. Finding it stops discussion. Failure to find it kills the

false conceit of knowledge. Only when you deduce a possible sensation

for me from your theory, and give it to me when and where the theory

requires, do I begin to be sure that your thought has anything to do

with truth.

_Pure sensations can only be realized in the earliest days of life._

They are all but impossible to adults with memories and stores of

associations acquired. Prior to all impressions on sense-organs the

brain is plunged in deep sleep and consciousness is practically

non-existent. Even the first weeks after birth are passed in almost

unbroken sleep by human infants. It takes a strong message from the

sense-organs to break this slumber. In a new-born brain this gives

rise to an absolutely pure sensation. But the experience leaves its

'unimaginable touch' on the matter of the convolutions, and the next

impression which a sense-organ transmits produces a cerebral reaction

in which the awakened vestige of the last impression plays its part.

Another sort of feeling and a higher grade of cognition are the

consequence; and the complication goes on increasing till the end of

life, no two successive impressions falling on an identical brain, and

no two successive thoughts being exactly the same. (See Vol. I, p. 230

ff.)

_The first sensation which an infant gets is for him the Universe._

And the Universe which he later comes to know is nothing but an

amplification and an implication of that first simple germ which,

by accretion on the one hand and intussusception on the other,

has grown so big and complex and articulate that its first estate

is unrememberable. In his dumb awakening to the consciousness of

_something there_, a mere _this_ as yet (or something for which

even the term _this_ would perhaps be too discriminative, and the

intellectual acknowledgment of which would be better expressed by

the bare interjection 'lo!'), the infant encounters an object in

which (though it be given in a pure sensation) all the 'categories

of the understanding' are contained. _It has objectivity, unity,

substantiality, causality, in the full sense in which any later object

or system of objects has these things._ Here the young knower meets

and greets his world; and the miracle of knowledge bursts forth, as

Voltaire says, as much in the infant's lowest sensation as in the

highest achievement of a Newton's brain. The physiological condition

of this first sensible experience is probably nerve-currents coming

in from many peripheral organs at once. Later, the one confused Fact

which these currents cause to appear is perceived to be many facts,

and to contain many qualities.[9] For as the currents vary, and the

brain-paths are moulded by them, other thoughts with other 'objects'

come, and the 'same thing' which was apprehended as a present _this_

soon figures as a past _that_, about which many unsuspected things have

come to light. The principles of this development have been laid down

already in Chapters XII and XIII, and nothing more need here be added

to that account.

"THE RELATIVITY OF KNOWLEDGE."

To the reader who is tired of so much _Erkenntnisstheorie_ I can only

say that I am so myself, but that it is indispensable, in the actual

state of opinions about Sensation, to try to clear up just what the

word means. Locke's pupils seek to do the impossible with sensations,

and against them we must once again insist that sensations 'clustered

together' cannot build up our more intellectual states of mind. Plato's

earlier pupils used to admit Sensation's existence, grudgingly, but

they trampled it in the dust as something corporeal, non-cognitive,

and vile.[10] His latest followers seem to seek to crowd it out of

existence altogether. The only reals for the neo-Hegelian writers

appear to be _relations_, relations without terms, or whose terms

are only speciously such and really consist in knots, or gnarls of

relations finer still _in infinitum_.

"Exclude from what we have considered real all qualities constituted

by relation, we find that none are left." "Abstract the many relations

from the one thing and there is nothing.... Without the relations it

would not exist at all."[11] "The single feeling is nothing real."

"On the recognition of relations as constituting the _nature_ of

ideas, rests the possibility of any tenable theory of their reality."

Such quotations as these from the late T. H. Green[12] would be matters

of curiosity rather than of importance, were it not that sensationalist

writers themselves believe in a so-called 'Relativity of Knowledge,'

which, if they only understood it, they would see to be identical

with Professor Green's doctrine. They tell us that the relation of

sensations to each other is something belonging to their essence, and

that no one of them has an absolute content:

"That, e.g., black can only be felt in contrast to white, or at

least in distinction from a paler or a deeper black; similarly a

tone or a sound only in alternation with others or with silence; and

in like manner a smell, a taste, a touch, only, so to speak, _in

statu nascendi_, whilst, when the stimulus continues, all sensation

disappears. This all seems at first sight to be splendidly consistent

both with itself and with the facts. But looked at more closely, it is

seen that neither is the case."[13]

The two leading facts from which the doctrine of universal relativity

derives its wide-spread credit are these:

1) The _psychological fact_ that so much of our actual knowledge _is_

of the relations of things--even our simplest sensations in adult life

are habitually referred to classes as we take them in; and

2) The _physiological fact_ that our senses and brain must have periods

of change and repose, else we cease to feel and think.

Neither of these facts proves anything about the presence or

non-presence to our mind of absolute qualities with which we become

sensibly acquainted. Surely not the psychological fact; for our

inveterate love of relating and comparing things does not alter the

intrinsic qualities or nature of the things compared, or undo their

absolute givenness. And surely not the physiological fact; for the

length of time during which we can feel or attend to a quality is

altogether irrelevant to the intrinsic constitution of the quality

felt. The time, moreover, is long enough in many instances, as

sufferers from neuralgia know.[14] And the doctrine of relativity,

not proved by these facts, is flatly disproved by other facts even

more patent. So far are we from not knowing (in the words of Professor

Bain) "any one thing by itself, but only the difference between it

and another thing," that if this were true the whole edifice of our

knowledge would collapse. If all we felt were the _difference_ between

the _C_ and _D_, or _c_ and _d_, on the musical scale, that being the

same in the two pairs of notes, the pairs themselves would be the same,

and language could get along without substantives. But Professor Bain

does not mean seriously what he says, and we need spend no more time on

this vague and popular form of the doctrine.[15] The facts which seem

to hover before the minds of its champions are those which are best

described under the head of a physiological law.

THE LAW OF CONTRAST.

I will first enumerate the main facts which fall under this law, and

then remark upon what seems to me their significance for psychology.[16]

[Nowhere are the phenomena of contrast better exhibited, and their

laws more open to accurate study, than in connection with the sense

of sight. Here both kinds--simultaneous and successive--can easily be

observed, for they are of constant occurrence. Ordinarily they remain

unnoticed, in accordance with the general law of economy which causes

us to select for conscious notice only such elements of our object as

will serve us for æsthetic or practical utility, and to neglect the

rest; just as we ignore the double images, the _mouches volantes_,

etc., which exist for everyone, but which are not discriminated

without careful attention. But by attention we may easily discover

the general facts involved in contrast. We find that _in general the

color and brightness of one object always apparently affect the color

and brightness of any other object seen simultaneously with it or

immediately after_.

In the first place, if we look for a moment at any surface and then

turn our eyes elsewhere, the complementary color and opposite degree

of brightness to that of the first surface tend to mingle themselves

with the color and the brightness of the second. This is _successive

contrast_. It finds its explanation in the fatigue of the organ of

sight, causing it to respond to any particular stimulus less and

less readily the longer such stimulus continues to act. This is

shown clearly in the very marked changes which occur in case of

continued fixation of one particular point of any field. The field

darkens slowly, becomes more and more indistinct, and finally, if

one is practised enough in holding the eye perfectly steady, slight

differences in shade and color may entirely disappear. If we now turn

aside the eyes, a negative after-image of the field just fixated at

once forms, and mingles its sensations with those which may happen to

come from anything else looked at. This influence is distinctly evident

only when the first surface has been 'fixated' without movement of

the eyes. It is, however, none the less present at all times, even

when the eye wanders from point to point, causing each sensation to

be modified more or less by that just previously experienced. On this

account successive contrast is almost sure to be present in cases of

simultaneous contrast, and to complicate the phenomena.

A _visual image is modified not only by other sensations just

previously experienced, but also by all those experienced

simultaneously with it, and especially by such as proceed from

contiguous portions of the retina_. This is the phenomenon of

_simultaneous contrast_. In this, as in successive contrast, both

brightness and hue are involved. A bright object appears still brighter

when its surroundings are darker than itself, and darker when they are

brighter than itself. Two colors side by side are apparently changed by

the admixture, with each, of the complement of the other. And lastly,

a gray surface near a colored one is tinged with the complement of the

latter.[17]

The phenomena of simultaneous contrast in sight are so complicated

by other attendant phenomena that it is difficult to isolate

them and observe them in their purity. Yet it is evidently of the

greatest importance to do so, if one would conduct his investigations

accurately. Neglect of this principle has led to many mistakes being

made in accounting for the facts observed. As we have seen, if the eye

is allowed to wander here and there about the field as it ordinarily

does, successive contrast results and allowance must be made for

its presence. It can be avoided only by carefully fixating with the

well-rested eye a point of one field, and by then observing the changes

which occur in this field when the contrasting field is placed by its

side. Such a course will insure pure simultaneous contrast. But even

thus it lasts in its purity for a moment only. It reaches its maximum

of effect immediately after the introduction of the contrasting field,

and then, if the fixation is continued, it begins to weaken rapidly

and soon disappears; thus undergoing changes similar to those observed

when any field whatever is fixated steadily and the retina becomes

fatigued by unchanging stimuli. If one continues still further to

fixate the same point, the color and brightness of one field tend to

spread themselves over and mingle with the color and brightness of the

neighboring fields, thus substituting '_simultaneous induction_' for

simultaneous contrast.

Not only must we recognize and eliminate the effects of successive

contrast, of temporal changes due to fixation, and of simultaneous

induction, in analyzing the phenomena of simultaneous contrast, but we

must also take into account _various other influences which modify its

effects_. Under favorable circumstances the contrast-effects are very

striking, and did they always occur as strongly they could not fail to

attract the attention. But they are not always clearly apparent, owing

to various disturbing causes which form no exception to the laws of

contrast, but which have a modifying effect on its phenomena. When,

for instance, the ground observed has many distinguishable features--a

_coarse grain, rough surface, intricate pattern,_ etc.--the contrast

effect appears weaker. This does not imply that the effects of contrast

are absent, but merely that the resulting sensations are overpowered

by the many other stronger sensations which entirely occupy the

attention. On such a ground a faint negative after-image--undoubtedly

due to retinal modifications--may become invisible; and even weak

objective differences in color may become imperceptible. For example, a

faint spot or grease-stain on woollen cloth, easily seen at a distance,

when the fibres are not distinguishable, disappears when closer

examination reveals the intricate nature of the surface.

Another frequent cause of the apparent absence of contrast is the

presence of narrow dark intermediate fields, such as are formed by

_bordering a field with black lines, or by the shaded contours of

objects_. When such fields interfere with the contrast, it is because

black and white can absorb much color without themselves becoming

clearly colored; and because such lines separate other fields too far

for them to distinctly influence one another. Even weak objective

differences in color may be made imperceptible by such means.

A third case where contrast does not clearly appear is where the _color

of the contrasting fields is too weak or too intense_, or where there

is _much difference in brightness between the two fields_. In the

latter case, as can easily be shown, it is the contrast of brightness

which interferes with the color-contrast and makes it imperceptible.

For this reason contrast shows best between fields of about equal

brightness. But the intensity of the color must not be too great, for

then its very darkness necessitates a dark contrasting field which

is too absorbent of induced color to allow the contrast to appear

strongly. The case is similar if the fields are too light.

_To obtain the best contrast-effects, therefore, the contracting fields

should be near together, should not be separated by shadows or black

lines, should be of homogeneous texture, and should be of about equal

brightness and medium intensity of color._ Such conditions do not

often occur naturally, the disturbing influences being present in case

of almost all ordinary objects, thus making the effects of contrast

far less evident. To eliminate these disturbances and to produce the

conditions most favorable for the appearance of good contrast-effects,

various experiments have been devised, which will be explained in

comparing the rival theories of explanation.

* * * * *

There are _two theories--the psychological and the

physiological_--which attempt to explain the phenomena of contrast.

Of these the _psychological one_ was the first to gain prominence.

_Its most able advocate has been Helmholtz. It explains contrast

as a_ DECEPTION OF JUDGMENT. In ordinary life our sensations have

interest for us only so far as they give us practical knowledge.

Our chief concern is to recognize objects, and we have no occasion

to estimate exactly their absolute brightness and color. Hence we

gain no facility in so doing, but neglect the constant changes in

their shade, and are very uncertain as to the exact degree of their

brightness or tone of their color. When objects are near one another

"we are inclined to consider those differences which are clearly and

surely perceived as greater than those which appear uncertain in

perception or which must be judged by aid of memory,"[18] just as we

see a medium-sized man taller than he really is when he stands beside

a short man. Such deceptions are more easily possible in the judgment

of small differences than of large ones; also where there is but one

element of difference instead of many. In a large number of cases of

contrast, in all of which a whitish spot is surrounded on all sides

by a colored surface--Meyer's experiment, the mirror experiment,

colored shadows, etc., soon to be described--the contrast is produced,

according to Helmholtz, by the fact that "a colored illumination or a

transparent colored covering appears to be spread out over the field,

and observation does not show directly that it fails on the white

spot."[19] We therefore believe that we see the latter through the

former color. Now

"Colors have their greatest importance for us in so far as they are

properties of bodies and can serve as signs for the recognition

of bodies.... We have become accustomed, in forming a judgment in

regard to the colors of bodies, to eliminate the varying brightness

and color of the illumination. We have sufficient opportunity to

investigate the same colors of objects in full sunshine, in the blue

light of the clear sky, in the weak white light of a cloudy day, in

the reddish-yellow light of the sinking sun or of the candle. Moreover

the colored reflections of surrounding objects are involved. Since

we see the same colored objects under these varying illuminations,

we learn to form a correct conception of the color of the object in

spite of the difference in illumination, i.e. to judge how such an

object would appear in white illumination; and since only the constant

color of the object interests us, we do not become conscious of the

particular sensations on which our judgment rests. So also we are

at no loss, when we see an object through a colored covering, to

distinguish what belongs to the color of the covering and what to

the object. In the experiments mentioned we do the same also where

the covering over the object is not at all colored, because of the

deception into which we fall, and in consequence of which we ascribe

to the body a false color, the color complementary to the colored

portion of the covering."[20]

We think that we see the complementary color through the colored

covering,--for these two colors together would give the sensation of

white which is actually experienced. If, however, in any way the white

spot is recognized as an independent object, or if it is compared with

another object known to be white, our judgment is no longer deceived

and the contrast does not appear.

"As soon as the contrasting field is recognized as an independent

body which lies above the colored ground, or even through an adequate

tracing of its outlines is seen to be a separate field, the contrast

disappears. Since, then, the judgment of the spatial position, the

material independence, of the object in question is decisive for the

determination of its color, it follows that the contrast-color arises

not through an act of sensation but through an act of judgment."[21]

In short, the apparent change in color or brightness through contrast

is due to no change in excitation of the organ, to no change in

sensation; but in consequence of a false judgment the unchanged

sensation is wrongly interpreted, and thus leads to a changed

_perception_ of the brightness or color.

* * * * *

In opposition to this theory has been developed one which attempts to

explain all cases of contrast as depending purely on _physiological

action of the terminal apparatus of vision. Hering is the most

prominent supporter of this view._ By great originality in devising

experiments and by insisting on rigid care in conducting them, he has

been able to detect the faults in the psychological theory and to

practically establish the validity of his own. Every visual sensation,

he maintains, is correlated to a physical process in the nervous

apparatus. Contrast is occasioned, not by a false idea resulting from

unconscious conclusions, but by the fact that the excitation of any

portion of the retina--and the consequent sensation--depends not only

on its own illumination, but on that of the rest of the retina as well.

"If this psycho-physical process is aroused, as usually happens, by

light-rays impinging on the retina, its nature depends not only on

the nature of these rays, but also on the constitution of the entire

nervous apparatus which is connected with the organ of vision, and on

the state in which it finds itself."[22]

When a limited portion of the retina is aroused by external stimuli,

the rest of the retina, and especially the immediately contiguous

parts, tends to react also, and in such a way as to produce

therefrom the sensation of the opposite degree of brightness and the

complementary color to that of the directly-excited portion. When a

gray spot is seen alone, and again when it appears colored through

contrast, the objective light from the spot is in both cases the same.

Helmholtz maintains that the neural process and the corresponding

_sensation_ also remain unchanged, but are differently _interpreted_;

Hering, that the neural process and the sensation are themselves

changed, and that the 'interpretation' is the direct conscious

correlate of the altered retinal conditions. According to the one, the

contrast is psychological in its origin; according to the other, it is

purely physiological. In the cases cited above where the contrast-color

is no longer apparent--on a ground with many distinguishable features,

on a field whose borders are traced with black lines, etc.,--the

psychological theory, as we have seen, attributes this to the fact

that under these circumstances we judge the smaller patch of color to

be an independent object on the surface, and are no longer deceived

in judging it to be something over which the color of the ground is

drawn. The physiological theory, on the other hand, maintains that the

contrast-effect is still produced, but that the conditions are such

that the slight changes in color and brightness which it occasions

become imperceptible.

* * * * *

The two theories, stated thus broadly, may seem equally plausible.

Hering, however, has conclusively proved, by experiments with

after-images, that the process on one part of the retina does modify

that on neighboring portions, under conditions where deception of

judgment is impossible.[23] A careful examination of the facts of

contrast will show that its phenomena must be due to this cause. _In

all the cases which one may investigate it will be seen that the

upholders of the psychological theory have failed to conduct their

experiments with sufficient care._ They have not excluded successive

contrast, have overlooked the changes due to steady fixation, and have

failed to properly account for the various modifying influences which

have been mentioned above. We can easily establish this if we examine

the most striking experiments in simultaneous contrast.

Of these one of the best known and most easily arranged is that known

as _Meyer's experiment_. A scrap of gray paper is placed on a colored

background, and both are covered by a sheet of transparent white paper.

The gray spot then assumes a contrast-color, complementary to that of

the background, which shines with a whitish tinge through the paper

which covers it. Helmholtz explains the phenomenon thus:

"If the background is green, the covering-paper itself appears to be

of a greenish color. If now the substance of the paper extends without

apparent interruption over the gray which lies under it, we think that

we see an object glimmering through the greenish paper, and such an

object must in turn be rose-red, in order to give white light. If,

however, the gray spot has its limits so fixed that it appears to be

an independent object, the continuity with the greenish portion of the

surface fails, and we regard it as a gray object which lies on this

surface."[24]

The contrast-color may thus be made to disappear by tracing in black

the outlines of the gray scrap, or by placing above the tissue paper

another gray scrap of the same degree of brightness, and comparing

together the two grays. On neither of them does the contrast-color now

appear.

Hering[25] shows clearly that this interpretation is incorrect, and

that the disturbing factors are to be otherwise explained. In the first

place, the experiment can be so arranged that we could not possibly be

deceived into believing that we see the gray through a colored medium.

Out of a sheet of gray paper cut strips 5 mm. wide in such a way that

there will be alternately an empty space and a bar of gray, both of the

same width, the bars being held together by the uncut edges of the gray

sheet (thus presenting an appearance like a gridiron). Lay this on a

colored background--e.g. green--cover both with transparent paper, and

above all put a black frame which covers all the edges, leaving visible

only the bars, which are now alternately green and gray. The gray bars

appear strongly colored by contrast, although, since they occupy as

much space as the green bars, we are not deceived into believing that

we see the former through a green medium. The same is true if we weave

together into a basket pattern narrow strips of green and gray and

cover them with the transparent paper.

Why, then, if it is a true sensation due to physiological causes, and

not an error of judgment, which causes the contrast, does the color

disappear when the outlines of the gray scrap are traced, enabling us

to recognize it as an independent object? In the first place, it does

not necessarily do so, as will easily be seen if the experiment is

tried. The contrast-color often remains distinctly visible in spite

of the black outlines. In the second place, there are many adequate

reasons why the effect should be modified. Simultaneous contrast is

always strongest at the border-line of the two fields; but a narrow

black field now separates the two, and itself by contrast strengthens

the whiteness of both original fields, which were already little

saturated in color; and on black and on white, contrast-colors show

only under the most favorable circumstances. Even weak objective

differences in color may be made to disappear by such tracing of

outlines, as can be seen if we place on a gray background a scrap of

faintly-colored paper, cover it with transparent paper and trace its

outlines. Thus we see that it is not the recognition of the contrasting

field as an independent object which interferes with its color, but

rather a number of entirely explicable physiological disturbances.

The same may be proved in the case of holding above the tissue paper a

second gray scrap and comparing it with that underneath. To avoid the

disturbances caused by using papers of different brightness, the second

scrap should be made exactly like the first by covering the same gray

with the same tissue paper, and carefully cutting a piece about 10 mm.

square out of both together. To thoroughly guard against successive

contrast, which so easily complicates the phenomena, we must carefully

prevent all previous excitation of the retina by colored light. This

may be done by arranging thus: Place the sheet of tissue paper on a

glass pane, which rests on four supports; under the paper put the first

gray scrap. By means of a wire, fasten the second gray scrap 2 or 3 cm.

above the glass plate. Both scraps appear exactly alike, except at the

edges. Gaze now at both scraps, with eyes not exactly accommodated, so

that they appear near one another, with a very narrow space between.

Shove now a colored field (green) underneath the glass plate, and the

contrast appears at once on both scraps. If it appears less clearly

on the upper scrap, it is because of its bright and dark edges, its

inequalities, its grain, etc. When the accommodation is exact, there is

no essential change, although then on the upper scrap the bright edge

on the side toward the light, and the dark edge on the shadow side,

disturb somewhat. By continued fixation the contrast becomes weaker

and finally yields to simultaneous induction, causing the scraps to

become indistinguishable from the ground. Remove the green field and

both scraps become green, by successive induction. If the eye moves

about freely these last-named phenomena do not appear, but the contrast

continues indefinitely and becomes stronger. When Helmholtz found that

the contrast on the lower scrap disappeared, it was evidently because

he then really held the eye fixed. This experiment may be disturbed by

holding the upper scrap wrongly and by the differences in brightness of

its edges, or by other inequalities, but not by that recognizing of it

'as an independent body lying above the colored ground,' on which the

psychological explanation rests.

In like manner the claims of the psychological explanation can be

shown to be inadequate in other cases of contrast. Of frequent use

are revolving disks, which are especially efficient in showing good

contrast-phenomena, because all inequalities of the ground disappear

and leave a perfectly homogeneous surface. On a white disk are arranged

colored sectors, which are interrupted midway by narrow black fields in

such a way that when the disk is revolved the white becomes mixed with

the color and the black, forming a colored disk of weak saturation on

which appears a gray ring. The latter is colored by contrast with the

field which surrounds it. Helmholtz explains the fact thus:

"The difference of the compared colors appears greater than it really

is either because this difference, when it is the only existing one

and draws the attention to itself alone, makes a stronger impression

than when it is one among many, or because the different colors of the

surface are conceived as alterations of the one ground-color of the

surface such as might arise through shadows falling on it, through

colored reflexes, or through mixture with colored paint or dust. In

truth, to produce an objectively gray spot on a green surface, a

reddish coloring would be necessary."[26]

This explanation is easily proved false by painting the disk with

narrow green and gray concentric rings, and giving each a different

saturation. The contrast appears though there is no ground-color, and

no longer a single difference, but many. The facts which Helmholtz

brings forward in support of his theory are also easily turned against

him. He asserts that if the color of the ground is too intense, or

if the gray ring is bordered by black circles, the contrast becomes

weaker; that no contrast appears on a white scrap held over the

colored field; and that the gray ring when compared with such scrap

loses its contrast-color either wholly or in part. Hering points out

the inaccuracy of all these claims. Under favorable conditions it is

impossible to make the contrast disappear by means of black enclosing

lines, although they naturally form a disturbing element; increase

in the saturation of the field, if disturbance through increasing

brightness-contrast is to be avoided, demands a darker gray field, on

which contrast-colors are less easily perceived; and careful use of the

white scrap leads to entirely different results. The contrast-color

does appear upon it when it is first placed above the colored field;

but if it is carefully fixated, the contrast-color diminishes very

rapidly both on it and on the ring, from causes already explained.

To secure accurate observation, all complication through successive

contrast should be avoided thus: first arrange the white scrap, then

interpose a gray screen between it and the disk, rest the eye, set the

wheel in motion, fixate the scrap, and then have the screen removed.

The contrast at once appears clearly, and its disappearance through

continued fixation can be accurately watched.

Brief mention of a few other cases of contrast must suffice. The

so-called mirror experiment consists of placing at an angle of 45º a

green (or otherwise colored) pane of glass, forming an angle with two

white surfaces, one horizontal and the other vertical. On each white

surface is a black spot. The one on the horizontal surface is seen

through the glass and appears dark green, the other is reflected from

the surface of the glass to the eye, and appears by contrast red. The

experiment may be so arranged that we are not aware of the presence of

the green glass, but think that we are looking directly at a surface

with green and red spots upon it; in such a case there is no deception

of judgment caused by making allowance for the colored medium through

which we think that we see the spot, and therefore the psychological

explanation does not apply. On excluding successive contrast by

fixation the contrast soon disappears as in all similar experiments.[27]

_Colored shadows_ have long been thought to afford a convincing proof

of the fact that simultaneous contrast is psychological in its origin.

They are formed whenever an opaque object is illuminated from two

separate sides by lights of different colors. When the light from one

source is white, its shadow is of the color of the other light, and

the second shadow is of a color complementary to that of the field

illuminated by both lights. If now we take a tube, blackened inside,

and through it look at the colored shadow, none of the surrounding

field being visible, and then have the colored light removed, the

shadow still appears colored, although 'the circumstances which

caused it have disappeared.' This is regarded by the psychologists as

conclusive evidence that the color is due to deception of judgment.

It can, however, easily be shown that the persistence of the color

seen through the tube is due to fatigue of the retina through the

prevailing light, and that when the colored light is removed the color

slowly disappears as the equilibrium of the retina becomes gradually

restored. When successive contrast is carefully guarded against, the

simultaneous contrast, whether seen directly or through the tube, never

lasts for an instant on removal of the colored field. The physiological

explanation applies throughout to all the phenomena presented by

colored shadows.[28]

If we have a small field whose illumination remains constant,

surrounded by a large field of changing brightness, an increase or

decrease in brightness of the latter results in a corresponding

apparent decrease or increase respectively in the brightness of the

former, while the large field seems to be unchanged. Exner says:

"This illusion of sense shows that we are inclined to regard as

constant the dominant brightness in our field of vision, and hence to

refer the changing difference between this and the brightness of a

limited field to a change in brightness of the latter."

The result, however, can be shown to depend not on illusion, but on

actual retinal changes, which alter the sensation experienced. The

irritability of those portions of the retina lighted by the large field

becomes much reduced in consequence of fatigue, so that the increase

in brightness becomes much less apparent than it would be without this

diminution in irritability. The small field, however, shows the change

by a change in the contrast-effect induced upon it by the surrounding

parts of the retina.[29]

The above cases show clearly that _physiological processes, and not

deception of judgment, are responsible for contrast of color_. To say

this, however, is not to maintain that our perception of a color is

never in any degree modified by our judgment of what the particular

colored thing before us may be. We have unquestionable illusions of

color due to wrong inferences as to what object is before us. Thus Von

Kries[30] speaks of wandering through evergreen forests covered with

snow, and thinking that through the interstices of the boughs he saw

the deep blue of pine-clad mountains, covered with snow and lighted by

brilliant sunshine; whereas what he really saw was the white snow on

trees near by, lying in shadow].[31]

Such a mistake as this is undoubtedly of psychological origin. It is

a wrong _classification_ of the appearances, due to the arousal of

intricate processes of association amongst which is the suggestion of a

different hue from that really before the eyes. In the ensuing chapters

such illusions as this will be treated of in considerable detail. But

it is a mistake to interpret the simpler cases of contrast in the light

of such illusions as these. These illusions can be rectified in an

instant, and we then wonder how they could have been. They come from

insufficient attention, or from the fact that the impression which we

get is a sign of more than one possible object, and can be interpreted

in either way. In none of these points do they resemble simple

color-contrast, which _unquestionably is a phenomenon of sensation

immediately aroused_.

* * * * *

I have dwelt upon the facts of color-contrast at such great length

because they form so good a text to comment on in my struggle

against the view that sensations are immutable psychic things which

coexist with higher mental functions. Both sensationalists and

intellectualists agree that such sensations exist. They _fuse_, say

the pure sensationalists, and _make_ the higher mental function;

they _are combined_ by activity of the Thinking Principle, say the

intellectualists. I myself have contended that they _do not exist_ in

or alongside of the higher mental function when that exists. The things

which arouse them exist; and the higher mental function also knows

these same things. But just as its knowledge of the things supersedes

and displaces their knowledge, so it supersedes and displaces them,

when it comes, being as much as they are a direct resultant of whatever

momentary brain-conditions may obtain. The psychological theory of

contrast, on the other hand, holds the sensations still to exist in

themselves unchanged before the mind, whilst the 'relating activity' of

the latter deals with them freely and settles to its own satisfaction

what each shall be, in view of what the others also are. Wundt says

expressly that the Law of Relativity is "not a law of sensation but

a law of Apperception;" and the word Apperception connotes with him

a higher intellectual spontaneity.[32] This way of taking things

belongs with the philosophy that looks at the _data_ of sense as

something earth-born and servile, and the 'relating of them together'

as something spiritual and free. Lo! the spirit can even change the

intrinsic quality of the sensible facts themselves if by so doing it

can relate them better to each other! But (apart from the difficulty of

seeing how changing the sensations should relate them better) is it not

manifest that the relations are part of the 'content' of consciousness,

part of the 'object,' just as much as the sensations are? Why ascribe

the former exclusively to the _knower_ and the latter to the _known_?

The _knower_ is in every case a unique pulse of thought corresponding

to a unique reaction of the brain upon its conditions. All that the

facts of contrast show us is that the _same real thing_ may give us

quite different sensations when the conditions alter, and that we

must therefore be careful which one to select as the thing's truest

representative.

* * * * *

_There are many other facts beside the phenomena of contrast_ which

prove that _when two objects act together on us the sensation which

either would give alone becomes a different sensation_. A certain

amount of skin dipped in hot water gives the perception of a certain

heat. More skin immersed makes the heat much more intense, although

of course the water's heat is the same. A certain extent as well

as intensity, in the quantity of the stimulus is requisite for any

quality to be felt. Fick and Wunderli could not distinguish heat

from touch when both were applied through a hole in a card, and so

confined to a small part of the skin. Similarly there is a _chromatic

minimum_ of size in objects. The image they cast on the retina must

needs have a certain extent, or it will give no sensation of color

at all. Inversely, more intensity in the outward impression may make

the subjective object more extensive. This happens, as will be shown

in Chapter XIX, when the illumination is increased: The whole room

expands and dwindles according as we raise or lower the gas-jet. It is

not easy to explain any of these results as illusions of judgment due

to the inference of a wrong objective cause for the sensation which we

get. No more is this easy in the case of Weber's observation that a

thaler laid on the skin of the forehead feels heavier when cold than

when warm; or of Szabadföldi's observation that small wooden disks

when heated to 122° Fahrenheit often feel heavier than those which are

larger but not thus warmed;[33] or of Hall's observation that a heavy

point moving over the skin seems to go faster than a lighter one moving

at the same rate of speed.[34]

Bleuler and Lehmann some years ago called attention to a strange

idiosyncrasy found in some persons, and consisting in the fact that

impressions on the eye, skin, etc., were accompanied by distinct

sensations of _sound_.[35] _Colored hearing_ is the name sometimes

given to the phenomenon, which has now been repeatedly described. Quite

lately the Viennese aurist Urbantschitsch has proved that these cases

are only extreme examples of a very general law, and that all our

sense-organs influence each other's sensations.[36] The hue of patches

of color so distant as not to be recognized was immediately, in U.'s

patients, perceived when a tuning-fork was sounded close to the ear.

Sometimes, on the contrary, the field was darkened by the sound. The

acuity of vision was increased, so that letters too far off to be read

could be read when the tuning-fork was heard. Urbantschitsch, varying

his experiments, found that their results were mutual, and that sounds

which were on the limits of audibility became audible when lights of

various colors were exhibited to the eye. Smell, taste, touch, sense

of temperature, etc., were all found to fluctuate when lights were

seen and sounds were heard. Individuals varied much in the degree and

kind of effect produced, but almost every one experimented on seems to

have been in some way affected. The phenomena remind one somewhat of

the 'dynamogenic' effects of sensations upon the strength of muscular

contraction observed by M. Féré, and later to be described. The most

familiar examples of them seem to be the increase of _pain_ by noise

or light, and the increase of _nausea_ by all concomitant sensations.

Persons suffering in any way instinctively seek stillness and darkness.

* * * * *

Probably every one will agree that the best way of formulating all such

facts is physiological: it must be that the cerebral process of the

first sensation is reinforced or otherwise altered by the other current

which comes in. No one, surely, will prefer a psychological explanation

_here_. Well, it seems to me that _all_ cases of mental reaction

to a plurality of stimuli must be like these cases, and that the

physiological formulation is everywhere the simplest and the best. When

simultaneous red and green light make us see yellow, when three notes

of the scale make us hear a chord, it is not because the sensations of

red and of green and of each of the three notes enter the mind as such,

and there 'combine' or 'are combined by its relating activity' into

the yellow and the chord, it is because the larger sum of light-waves

and of air-waves arouses new cortical processes, to which the yellow

and the chord directly correspond. Even when the sensible qualities of

things enter into the objects of our highest thinking, it is surely

the same. Their several _sensations_ do not continue to exist there

tucked away. They are _replaced_ by the higher thought which, although

a different psychic unit from them, knows the same sensible qualities

which they know.

The principles laid down in Chapter VI seem then to be corroborated in

this new connection. _You cannot build up one thought or one sensation

out of many; and only direct experiment can inform us of what we shall

perceive when we get many stimuli at once._

THE 'ECCENTRIC PROJECTION' OF SENSATIONS.

We often hear the opinion expressed that all our sensations at first

appear to us as subjective or internal, and are afterwards and by a

special act on our part 'extradited' or 'projected' so as to appear

located in an outer world. Thus we read in Professor Ladd's valuable

work that

"Sensations... are psychical states _whose place_--so far as they

can be said to have one--_is the mind_. The transference of these

sensations from mere mental states to physical processes located

in the periphery of the body, or to qualities of things projected

in space external to the body, is a mental act. It may rather be

said to be a mental _achievement_ [cf. Cudworth, footnote 10,

as to knowledge being _conquering_], for it is an act which in

its perfection results from a long and intricate process of

development.... Two noteworthy stages, or 'epoch-making' achievements

in the process of elaborating the presentations of sense, require a

special consideration. These are '_localization_,' or the transference

of the composite sensations from mere states of the mind to processes

or conditions recognized as taking place at more or less definitely

fixed points or areas of the body; and '_eccentric projection_'

(sometimes called 'eccentric perception') or the giving to these

sensations an objective existence (in the fullest sense of the word

'objective') as qualities of objects situated within a field of space

and in contact with, or more or less remotely distant from, the

body."[37]

It seems to me that there is not a vestige of evidence for this view.

It hangs together with the opinion that our sensations are originally

devoid of all spatial content,[38] an opinion which I confess that I

am wholly at a loss to understand. As I look at my bookshelf opposite

I cannot frame to myself an idea, however imaginary, of any feeling

which I could ever possibly have got from it except the feeling of the

same big extended sort of outward fact which I now perceive. So far is

it from being true that our first way of feeling things is the feeling

of them as subjective or mental, that the exact opposite seems rather

to be the truth. Our earliest, most instinctive, least developed kind

of consciousness is the objective kind; and only as reflection becomes

developed do we become aware of an inner world at all. Then indeed

we enrich it more and more, even to the point of becoming idealists,

with the spoils of the outer world which at first was the only world

we knew. But subjective consciousness, aware of itself as subjective,

does not at first exist. Even an attack of pain is surely felt at first

objectively as something in space which prompts to motor reaction, and

to the very end it is located, not in the mind, but in some bodily part.

"A sensation which should not awaken an impulse to move, nor any

tendency to produce an outward effect, would manifestly be useless to

a living creature. On the principles of evolution such a sensation

could never be developed. Therefore every sensation originally refers

to something external and independent of the sentient creature.

Rhizopods (according to Engelmann's observations) retract their

pseudopodia whenever these touch foreign bodies, even if these

foreign bodies are the pseudopodia of other individuals of their

own species, whilst the mutual contact of their own pseudopodia is

followed by no such contraction. These low animals can therefore

already feel an outer world--even in the absence of innate ideas of

causality, and probably without any clear consciousness of space. In

truth the conviction that something exists outside of ourselves does

not come from thought. It comes from sensation; it rests on the same

ground as our conviction of our own existence.... If we consider the

behavior of new-born animals, we never find them betraying that they

are first of all conscious of their sensations as purely subjective

excitements. We far more readily incline to explain the astonishing

certainty with which they make use of their sensations (and which is

an effect of adaptation and inheritance) as the result of an inborn

intuition of the outer world.... Instead of starting from an original

pure subjectivity of sensation, and seeking how this could possibly

have acquired an objective signification, we must, on the contrary,

begin by the possession of objectivity by the sensation and then show

how for reflective consciousness the latter becomes interpreted as an

effect of the object, how in short the original immediate objectivity

becomes changed into a remote one."[39]

Another confusion, much more common than the denial of all objective

character to sensations, is the assumption that they are all originally

located _inside the body_ and are projected outward by a secondary

act. This secondary judgment is always false, according to M. Taine,

so far as the place of the sensation itself goes. But it happens to

_hit_ a real object which is at the point towards which the sensation

is projected; so we may call its result, according to this author, a

_veridical hallucination_.[40] The word Sensation, to begin with, is

constantly, in psychological literature, used as if it meant one and

the same thing with the _physical impression_ either in the terminal

organs or in the centres, which is its antecedent condition, and this

notwithstanding that by sensation we mean a mental, not a physical,

fact. But those who expressly mean by it a mental fact still leave to

it a physical _place_, still think of it as objectively inhabiting the

very neural tracts which occasion its appearance when they are excited;

and then (going a step farther) they think that it must _place itself_

where _they_ place it, or be subjectively sensible of that place as its

habitat in the first instance, and afterwards have to be _moved_ so as

to appear elsewhere.

All this seems highly confused and unintelligible. Consciousness, as

we saw in an earlier chapter (vol. I p. 214) cannot properly be said

to _inhabit_ any place. It has dynamic relations with the brain, and

cognitive relations with everything and anything. From the one point

of view _we_ may say that a sensation is in the same place with the

brain (if we like), just as from the other point of view we may say

that it is in the same place with whatever quality it may be cognizing.

But the supposition that a sensation primitively _feels either itself

or its object to be in the same place with the brain_ is absolutely

groundless, and neither _a priori_ probability nor facts from

experience can be adduced to show that such a deliverance forms any

part of the original cognitive function of our sensibility.

Where, then, do we feel the objects of our original sensations to be?

Certainly a child newly born in Boston, who gets a sensation from the

candle-flame which lights the bedroom, or from his diaper-pin, does

not feel either of these objects to be situated in longitude 72° W.

and latitude 41° N. He does not feel them to be in the third story of

the house. He does not even feel them in any distinct manner to be

to the right or the left of any of the other sensations which he may

be getting from other objects in the room at the same time. He does

not, in short, know anything _about_ their space-relations to anything

else in the world. The flame fills its own place, the pain fills its

own place; but as yet these places are neither identified with, nor

discriminated from, any other places. That comes later. For the places

thus first sensibly known are elements of the child's space-world which

remain with him all his life; and by memory and later experience he

learns a vast number of things _about_ those places which at first he

did not know. But to the end of time certain places of the world remain

defined for him as the places _where those sensations were_; and his

only possible answer to the question _where anything is_ will be to say

'_there_,' and to name some sensation or other like those first ones,

which shall identify the spot. Space _means_ but the aggregate of all

our possible sensations. There is no duplicate space known _aliunde_,

or created by an 'epoch-making achievement' into which our sensations,

originally spaceless, are dropped. They _bring_ space and all its

places to our intellect, and do not derive it thence.

By his body, then, the child later means simply _that place where_

the pain from the pin, and a lot of other sensations like it, were or

are felt. It is no more true to say that he locates that pain in his

body, than to say that he locates his body in that pain. Both are true:

that pain is part of what he _means by the word body_. Just so by the

outer world the child means nothing more than _that place where_ the

candle-flame and a lot of other sensations like it are felt. He no more

locates the candle in the outer world than he locates the outer world

in the candle. Once again, he does both; for the candle is part of what

he _means_ by 'outer world.'

* * * * *

This (it seems to me) will be admitted, and will (I trust) be made

still more plausible in the chapter on the Perception of Space. But the

later developments of this perception are so complicated that these

simple principles get easily overlooked. One of the complications

comes from the fact that things _move_, and that the original object

which we feel them to be splits into two parts, one of which remains as

their whereabouts and the other goes off as their quality or nature.

We then contrast where they _were_ with where they _are_. If _we_ do

not move, the sensation of _where they were_ remains unchanged; but we

ourselves presently move, so that that also changes; and 'where they

were' becomes no longer the actual sensation which it was originally,

but a sensation which we merely conceive as possible. Gradually the

system of these possible sensations, takes more and more the place of

the actual sensations. 'Up' and 'down' become 'subjective' notions;

east and west grow more 'correct' than 'right' and 'left' etc.; and

things get at last more 'truly' located by their relation to certain

ideal fixed co-ordinates than by their relation either to our bodies

or to those objects by which their place was originally defined. _Now

this revision of our original localizations is a complex affair; and

contains some facts which may very naturally come to be described as

translocations whereby sensations get shoved farther off than they

originally appeared._

Few things indeed are more striking than the changeable distance which

the objects of many of our sensations may be made to assume. A fly's

humming may be taken for a distant steam-whistle; or the fly itself,

seen out of focus, may for a moment give us the illusion of a distant

bird. The same things seem much nearer or much farther, according as we

look at them through one end or another of an opera-glass. Our whole

optical education indeed is largely taken up with assigning their

proper distances to the objects of our retinal sensations. An infant

will grasp at the moon; later, it is said, he projects that sensation

to a distance which he knows to be beyond his reach. In the much quoted

case of the 'young gentleman who was born blind,' and who was 'couched'

for the cataract by Mr. Chesselden, it is reported of the patient

that "when he first saw, he was so far from making any judgment about

distances, that he thought all objects whatever touched his eyes (as he

expressed it) as what he felt did his skin." And other patients born

blind, but relieved by surgical operation, have been described as

bringing their hand close to their eyes to feel for the objects which

they at first saw, and only gradually stretching out their hand when

they found that no contact occurred. Many have concluded from these

facts that our earliest visual objects must seem in immediate contact

with our eyes.

But tactile objects also may be affected with a like ambiguity of

situation.

If one of the hairs of our head be pulled, we are pretty accurately

sensible of the direction of the pulling by the movements imparted to

the head.[41] But the feeling of the pull is localized, not in that

part of the hair's length which the fingers hold, but in the scalp

itself. This seems connected with the fact that our hair hardly serves

at all as a tactile organ. In creatures with _vibrissæ_, however, and

in those quadrupeds whose whiskers are tactile organs, it can hardly be

doubted that the feeling is projected out of the root into the shaft of

the hair itself. We ourselves have an approach to this when the beard

as a whole, or the hair as a whole, is touched. We perceive the contact

at some distance from the skin.

When fixed and hard appendages of the body, like the teeth and nails,

are touched, we feel the contact where it objectively is, and not

deeper in, where the nerve-terminations lie. If, however, the tooth is

loose, we feel two contacts, spatially separated, one at its root, one

at its top.

From this ease to that of a hard body not organically connected with

the surface, but only accidentally in contact with it, the transition

is immediate. With the point of a cane we can trace letters in the air

or on a wall just as with the finger-tip; and in so doing feel the size

and shape of the path described by the cane's tip just as immediately

as, without a cane, we should feel the path described by the tip of our

finger. Similarly the draughtsman's immediate perception seems to be of

the point of his pencil, the surgeon's of the end of his knife, the

duellist's of the tip of his rapier as it plunges through his enemy's

skin. When on the middle of a vibrating ladder, we feel not only our

feet on the round, but the ladder's feet against the ground far below.

If we shake a locked iron gate we feel the middle, on which our hands

rest, move, but we equally feel the stability of the ends where the

hinges and the lock are, and we seem to feel all three at once.[42] And

yet the place where the contact is _received_ is in all these cases the

skin, whose sensations accordingly are sometimes interpreted as objects

on the surface, and at other times as objects a long distance off.

We shall learn in the chapter on Space that our feelings of our

own movement are principally due to the sensibility of our rotating

_joints_. Sometimes by fixing the attention, say on our elbow-joint,

we can feel the movement in the joint itself; but we always are

simultaneously conscious of the path which during the movement our

finger-tips describe through the air, and yet these same finger-tips

themselves are in no way physically modified by the motion. A blow on

our ulnar nerve behind the elbow is felt both there and in the fingers.

Refrigeration of the elbow produces pain in the fingers. Electric

currents passed through nerve-trunks, whether of cutaneous or of more

special sensibility (such as the optic nerve), give rise to sensations

which are vaguely localized beyond the nerve-tracts traversed. Persons

whose legs or arms have been amputated are, as is well known, apt to

preserve an illusory feeling of the lost hand or foot being there. Even

when they do not have this feeling constantly, it may be occasionally

brought back. This sometimes is the result of exciting electrically the

nerve-trunks buried in the stump.

"I recently faradized," says Dr. Mitchell, "a case of disarticulated

shoulder without warning my patient of the possible result. For two

years he had altogether ceased to feel the limb. As the current

affected the brachial plexus of nerves he suddenly cried aloud, 'Oh

the hand,--the hand!' and attempted to seize the missing member. The

phantom I had conjured up swiftly disappeared, but no spirit could

have more amazed the man, so real did it seem."[43]

Now the apparent position of the lost extremity varies. Often the foot

seems on the ground, or follows the position of the artificial foot,

where one is used. Sometimes where the arm is lost the elbow will seem

bent, and the hand in a fixed position on the breast. Sometimes, again,

the position is non-natural, and the hand will seem to bud straight

out of the shoulder, or the foot to be on the same level with the knee

of the remaining leg. Sometimes, again, the position is vague; and

sometimes it is ambiguous, as in another patient of Dr. Weir Mitchell's

who

"lost his leg at the age of eleven, and remembers that the foot by

degrees approached, and at last reached the knee. When he began to

wear an artificial leg it reassumed in time its old position, and he

is never at present aware of the leg as shortened, unless for some

time he talks and thinks of the stump, and of the missing leg, when ...

the direction of attention to the part causes a feeling of discomfort,

and the subjective sensation of active and unpleasant movement of the

toes. With these feelings returns at once the delusion of the foot as

being placed at the knee."

All these facts, and others like them, can easily be described as if

our sensations might be induced by circumstances to migrate from their

_original locality_ near the brain or near the surface of the body, and

to appear farther off; and (under different circumstances) to return

again after having migrated. But a little analysis of what happens

shows us that this description is inaccurate.

_The objectivity with which each of our sensations originally comes to

us, the roomy and spatial character which is a primitive part of its

content, is not in the first instance relative to any other sensation._

The first time we open our eyes we get an optical object which is _a

place_, but which is not yet _placed_ in relation to any other object,

nor identified with any place otherwise known. It is a place with

which so far we are only _acquainted_. When later we know that this

same place is in 'front' of us, that only means that we have learned

something _about_ it, namely, that it is _congruent with that_ _other_

place, called 'front,' which is given us by certain sensations of the

arm and hand or of the head and body. But at the first moment of our

optical experience, even though we already had an acquaintance with

our head, hand, and body, we could not possibly know anything about

their relations to this new seen object. It could not be immediately

located in respect of _them_. How its place agrees with the places

which their feelings yield is a matter of which only later experience

can inform us; and in the next chapter we shall see with some detail

how later experience does this by means of discrimination, association,

selection, and other constantly working functions of the mind. When,

therefore, the baby grasps at the moon, that does not mean that what

he sees fails to give him the sensation which he afterwards knows

as distance; it means only that he has not learned at what _tactile

or manual distance_ things which appear at that _visual distance_

are.[44] And when a person just operated for cataract gropes close to

his face for far-off objects, that only means the same thing. All the

ordinary optical signs of differing distances are absent from the poor

creature's sensation anyhow. His vision is monocular (only one eye

being operated at a time); the lens is gone, and everything is out of

focus; he feels photophobia, lachrymation, and other painful resident

sensations of the eyeball itself, whose place he has long since learned

to know in tactile terms; what wonder, then, that the first tactile

reaction which the new sensations provoke should be one associated with

the tactile situation of the organ itself? And as for his assertions

about the matter, what wonder, again, if, as Prof. Paul Janet says,

they are still expressed in the tactile language which is the only

one he knows. "_To be touched_ means for him to receive an impression

without first making a movement." His eye gets such an impression now;

so he can only say that the objects are 'touching it.'

"All his language, borrowed from touch, but applied to the objects

of his sight, make us think that he perceives differently from

ourselves, whereas, at bottom, it is only his different way of

talking about the same experience."[45]

The other cases of translocation of our sensations are equally easily

interpreted without supposing any 'projection' from a centre at which

they are originally perceived. Unfortunately the details are intricate;

and what I say now can only be made fully clear when we come to the

next chapter. We shall then see that we are constantly selecting

certain of our sensations as _realities_ and degrading others to the

status of _signs_ of these. When we get one of the signs we think of

the reality signified; and the strange thing is that then the reality

(which need not be itself a sensation at all at the time, but only an

idea) is so interesting that it acquires an hallucinatory strength,

which may even eclipse that of the relatively uninteresting sign and

entirely divert our attention from the latter. Thus the sensations to

which our joints give rise when they rotate are signs of what, through

a large number of other sensations, tactile and optical, we have come

to know as the movement of the whole limb. This movement of the whole

limb is what we _think of_ when the joint's nerves are excited in

that way; and _its_ place is so much more important than the joint's

place that our sense of the latter is taken up, so to speak, into our

perception of the former, and the sensation of the movement seems to

diffuse itself into our very fingers and toes. But by abstracting our

attention from the suggestion of the entire extremity we can perfectly

well perceive the same sensation as if it were concentrated in one

spot. We can identify it with a differently located tactile and visual

image of 'the joint' itself.

Just so when we feel the tip of our cane against the ground. The

peculiar sort of movement of the hand (impossible in one direction,

but free in every other) which we experience when the tip touches 'the

ground,' is a sign to us of the visual and tactile object which we

already know under that name. We think of 'the ground' as being there

and giving us the sensation of this kind of movement. The sensation,

we say, comes _from_ the ground. The ground's place seems to be its

place; although at the same time, and for very similar practical

reasons, we think of another optical and tactile object, 'the hand'

namely, and consider that _its_ place _also_ must be the place of our

sensation. In other words, we take an object or sensible content A,

and confounding it with another object otherwise known, B, or with

two objects otherwise known, B and C, we identify its place with

their places. But in all this there is _no 'projecting'_ (such as the

extradition-philosophers talk of) of A out of an _original_ place; no

primitive location which it first occupied, _away from_ these other

sensations, has to be contradicted; no natural 'centre,' from which it

is expelled, exists. That would imply that A aboriginally came to us in

definite local relations with other sensations, for to be _out_ of B

and C is to be in local relation with them as much as to be _in_ them

is so. But it was no more out of B and C than it was in them when it

first came to us. It simply had nothing to do with them. To say that

we feel a sensation's seat to be 'in the brain' or 'against the eye'

or 'under the skin' is to say as much _about_ it and to deal with it

in as non-primitive a way as to say that it is a mile off. These are

all secondary perceptions, ways of defining the sensation's seat _per

aliud_. They involve numberless associations, identifications, and

imaginations, and admit a great deal of vacillation and uncertainty in

the result.[46]

* * * * *

_I conclude, then, that there is no truth in the 'eccentric projection'

theory_. It is due to the confused assumption that the bodily processes

which cause a sensation must also be its seat.[47] But sensations

have no seat in this sense. They _become_ seats for each other, as

fast as experience associates them together; but that violates no

primitive seat possessed by any one of them. And though our sensations

cannot then so analyze and talk of themselves, yet at their very first

appearance quite as much as at any later date are they cognizant of

all those qualities which we end by extracting and conceiving under

the names of _objectivity, exteriority,_ and _extent_. It is surely

subjectivity and interiority which are the notions _latest_ acquired by

the human mind.[48]

* * * * *

[1] Some persons will say that we never have a really simple object or

content. My definition of sensation does not require the simplicity

to be absolutely, but only relatively, extreme. It is worth while in

passing, however, to warn the reader against a couple of inferences

that are often made. One is that because we gradually learn to analyze

so many qualities we ought to conclude that there are no really

indecomposable feelings in the mind. The other is that because the

processes that produce our sensations are multiple, the sensations

regarded as subjective facts must also be compound. To take an example,

to a child the taste of lemonade comes at first as a simple quality. He

later learns both that many stimuli and many nerves are involved in the

exhibition of this taste to his mind, and he also learns to perceive

separately the sourness, the coolness, the sweet, the lemon aroma,

etc., and the several degrees of strength of each and all of these

things,--the experience falling into a large number of aspects, each

of which is abstracted, classed, named, etc., and all of which appear

to be the elementary sensations into which the original 'lemonade

flavor' is decomposed. It is argued from this that the latter never was

the simple thing which it seemed. I have already criticised this sort

of reasoning in Chapter VI (see pp. 170 ff.). The mind of the child

enjoying the simple lemonade flavor and that of the same child grown up

and analyzing it are in two entirely different conditions. Subjectively

considered, the two states of mind are two altogether distinct sorts

of fact. The later mental state says 'this is the _same flavor (or

fluid)_ which that earlier state perceived as simple,' but that does

not make the two states themselves identical. It is nothing but a case

of learning more and more _about_ the same topics of discourse or

things.--Many of these topics, however, must be confessed to resist

all analysis, the various colors for example. He who sees blue and

yellow 'in' a certain green means merely that when green is confronted

with these other colors he sees relations of _similarity_. He who sees

abstract 'color' in it means merely that he sees a similarity between

it and all the other objects known as colors. (Similarity itself

cannot ultimately be accounted for by an identical abstract element

buried in all the similars, as has been already shown, p. 492 ff.)

He who sees abstract paleness, intensity, purity, in the green means

other similarities still. These are all outward determinations of that

special green, knowledges _about_ it, _zufällige Ansichten_, as Herbart

would say, not _elements_ of its composition. Compare the article by

Meinong in the Vierteljahrschrift für wiss. Phil., xii. 324.

[2] See Vol. I, p. 221.

[3] Those who wish a fuller treatment than Martin's Human Body affords

may be recommended to Bernstein's 'Five Senses of Man,' in the

International Scientific Series, or to Ladd's or Wundt's Physiological

Psychology. The completest compendium is L. Hermann's Handbuch der

Physiologie, vol. iii.

[4] "The sensations which we _postulate_ as the signs or occasions

of our perceptions" (A. Seth: Scottish Philosophy, p. 89). "Their

existence is _supposed_ only because, without them, it would be

impossible to account for the complex phenomena which are directly

present in consciousness" (J. Dewey: Psychology, p. 34). Even as

great an enemy of Sensation as T. H. Green has to allow it a sort

of hypothetical existence under protest. "Perception presupposes

feeling" (Contemp. Review, vol. xxxi. p. 747). Cf. also such passages

as those in his Prolegomena to Ethics, §§ 48, 49.--Physiologically,

the sensory and the reproductive or associative processes may wax

and wane independently of each other. Where the part directly due

to stimulation of the sense-organ preponderates, the thought has

a sensational character, and differs from other thoughts in the

sensational direction. Those thoughts which lie farthest in that

direction we call _sensations_, for practical convenience, just as we

call _conceptions_ those which lie nearer the opposite extreme. But we

no more have conceptions pure than we have pure sensations. Our most

rarefied intellectual states involve some bodily sensibility, just

as our dullest feelings have some intellectual scope. Common-sense

and common psychology express this by saying that the mental state is

composed of distinct fractional _parts_, one of which is sensation, the

other conception. We, however, who believe every mental state to be an

integral thing (Vol. I. p. 276) cannot talk thus, but must speak of the

degree of sensational or intellectual character, or function, of the

mental state. Professor Hering puts, as usual, his finger better upon

the truth than any one else. Writing of visual perception, he says: "It

is inadmissible in the present state of our knowledge to assert that

first and last the same retinal picture arouses exactly the same _pure

sensation_, but that this sensation, in consequence of practice and

experience, is differently _interpreted_ the last time, and elaborated

into a different perception from the first. For the only real _data_

are, on the one hand, the physical picture on the retina,--and that is

both times the same; and, on the other hand, the resultant state of

consciousness (_ausgeloste Empfindungscomplex_)--and that is both times

distinct. _Of any third thing, namely, a pure sensation thrust between

the retinal and the mental pictures, we know nothing. We can then, if

we wish to avoid all hypothesis, only say that the nervous apparatus

reacts upon the same stimulus differently the last time from the

first, and that in consequence the consciousness is different too._"

(Hermann's Hdbch., iii. i. 567-8.)

[5] Yet even writers like Prof. Bain will deny, in the most gratuitous

way, that sensations know anything. "It is evident that the lowest

or most restricted form of sensation does not contain an element of

knowledge. The mere state of mind called the sensation of scarlet

is not knowledge, although a necessary preparation for it." 'Is not

knowledge _about_ scarlet' is all that Professor Bain can rightfully

say.

[6] By simple ideas of sensation Locke merely means sensations.

[7] Essay c. H. U., bk. ii. ch. xxiii. § 29; ch. xxv. § 9.

[8] _Op. cit_. bk. ii. ch. ii. § 2.

[9] "So far is it from being true that we necessarily have as many

feelings in consciousness at one time as there are inlets to the sense

then played upon, that it is a fundamental law of pure sensation that

each momentary state of the organism yields but one feeling, however

numerous may be its parts and its exposures.... To this original

Unity of consciousness it makes no difference that the tributaries

to the single feeling are beyond the organism instead of within it,

in an outside object with several sensible properties, instead of in

the living body with its several sensitive functions.... The unity

therefore is not made by 'association' of several components; but the

plurality is formed by _dissociation_ of unsuspected varieties within

the unity; the substantive thing being no product of synthesis, but

the residuum of differentiation." (J. Martineau: A Study of Religion

(1888), p. 193-4.) Compare also F. H. Bradley, Logic, book i. chap. ii.

[10] Such passages as the following abound in anti-sensationalist

literature: "Sense is a kind of dull, confused, and stupid perception

obtruded upon the soul from without, whereby it perceives the

alterations and motions within its own body, and takes cognizance

of individual bodies existing round about it, but does not clearly

comprehend what they are nor penetrate into the nature of them, it

being intended by nature, as Plotinus speaks, not so properly for

_knowledge_ as for the _use of the body_. For the soul suffering under

that which it perceives by way of _passion_ cannot master or _Conquer_

it, that is to say, know or understand it. For so Anaxagoras in

Aristotle very fitly expresses the nature of knowledge and intellection

under the notion of _Conquering_. Wherefore it is necessary, since

the mind understands all things, that it should be free from mixture

and passion, for this end, as Anaxagoras speaks, that it may be able

to _master and conquer_ its objects, that is to say, to _know and

understand_ them. In like manner Plotinus, in his book of Sense and

Memory, makes to _suffer_ and to _be conquered_ all one, as also to

_know_ and to _conquer_; for which reason he concludes that that which

suffers doth not know.... Sense that suffers from external objects

lies as it were prostrate under them, and is overcome by them....

Sense therefore is a certain kind of drowsy and somnolent perception

of that passive part of the soul which is as it were asleep in the

body, and acts concretely with it.... It is an energy arising from the

body and a certain kind of drowsy or sleeping life of the soul blended

together with it. The perceptions of which compound, or of the soul as

it were half asleep and half awake, are confused, indistinct, turbid,

and encumbered cogitations very different from the energies of the

noetical part,... which are free, clear, serene, satisfactory, and

awakened cogitations. That is to say, knowledges." Etc., etc., etc.

(R. Cudworth: Treatise concerning Eternal and Immutable Morality, bk.

iii. chap. ii.) Similarly Malebranche: "THÉODORE.--Oh, oh, Ariste! God

knows pain, pleasure, warmth, and the rest. But he does not feel these

things. He knows pain, since he knows what that modification of the

soul is in which pain consists. He knows it because he alone causes

it in us (as I shall presently prove), and he knows what he does. In

a word, he knows it because his knowledge has no bounds. But he does

not feel it, for if so he would be unhappy. To know pain, then, is

not to feel it. ARISTE.--That is true. But to feel it is to know it,

is it not? THÉODORE.--No indeed, since God does not feel it in the

least, and yet he knows it perfectly. But in order not to quibble about

terms, if you will have it that to feel pain is to know it, agree at

least that it is not to know it clearly, that it is not to know it by

light and by evidence--in a word, that it is not to know its nature; in

other words and to speak exactly, it is not to know it at all. To feel

pain, for example, is to feel ourselves unhappy without well knowing

either what we are or what is this modality of our being which makes us

unhappy.... Impose silence on your senses, your imagination, and your

passions, and you will hear the pure voice of inner truth, the clear

and evident replies of our common master. Never confound the evidence

which results from the comparison of ideas with the liveliness of the

sensations which touch and thrill you. The livelier our sensations and

feelings (_sentiments_) are, the more darkness do they shed. The more

terrible or agreeable are our phantoms, and the more body and reality

they appear to have, the more dangerous are they and fit to lead us

astray." (Entretiens sur la Métaphysique, 3me Entretien, _ad init._)

Malebranche's Théodore prudently does not try to explain how God's

'infinite felicity' is compatible with his not feeling joy.

[11] Green: Prolegomena, §§ 20, 28.

[12] Introd. to Hume, §§ 146, 188. It is hard to tell just what this

apostolic human being but strenuously feeble writer means by relation.

Sometimes it seems to stand for system of related fact. The ubiquity

of the 'psychologist's fallacy' (see Vol. I p. 196) in his pages, his

incessant leaning on the confusion between the thing known, the thought

that knows it, and the farther things known about that thing and about

that thought by later and additional thoughts, make it impossible to

clear up his meaning. Compare, however, with the utterances in the

text such others as these: "The waking of Self-consciousness from the

sleep of sense is an absolute new beginning, and nothing can come

within the 'crystal sphere' of intelligence except as it is determined

by intelligence. What sense is to sense is nothing for thought. What

sense is to thought, it is as determined _by_ thought. There can,

therefore, be no 'reality' in sensation to which the world of thought

can be referred." (Edward Caird's Philosophy of Kant, 1st ed. pp.

393-4.) "When," says Green again, "feeling a pain or pleasure of heat,

I perceive it to be connected with the action of approaching the fire,

am I not perceiving a relation _of which one constituent, at any rate,

is a simple sensation? The true answer is, No._" "Perception, in its

simplest form...--perception as the first sight or touch of an object

in which nothing but what is seen or touched is recognized--_neither

is nor contains sensation_" (Contemp. Rev., xxxi. pp. 746, 750.) "Mere

sensation is in truth a phrase that represents no reality." "Mere

feeling, then, as a matter unformed by thought, has no place in the

world of facts, in the cosmos of possible experience." (Prolegomena to

Ethics, §§ 46, 50.)--I have expressed myself a little more fully on

this subject in Mind, x. 27 ff.

[13] Stumpf: Tonpsychologie, i. pp. 7, 8. Hobbes's phrase, _sentire

semper idem et non sentire ad idem recidunt_, is generally treated as

the original statement of the relativity doctrine. J. S. Mill (Examn.

of Hamilton, p. 6) and Bain (Senses and Intellect, p. 321; Emotions

and Will, pp. 550, 570-2; Logic, i. p. 2; Body and Mind, p. 81) are

subscribers to this doctrine. Cf. also J. Mill's Analysis, J. S. Mill's

edition, II. 11, 12.

[14] We can steadily hear a note for half an hour. The differences

between the senses are marked. Smell and taste seem soon to get

fatigued.

[15] In the popular mind it is mixed up with that entirely different

doctrine of the 'Relativity of Knowledge' preached by Hamilton and

Spencer. This doctrine says that our knowledge is relative _to us_, and

is not of the object as the latter is in itself. It has nothing to do

with the question which we have been discussing, of whether our objects

of knowledge contain absolute terms or consist altogether of relations.

[16] What follows in brackets, as far as p. 27, is from the pen of my

friend and pupil Mr. E. B. Delabarre.

[17] These phenomena have close analogues in the phenomena of contrast

presented by the temperature-sense (see W. Preyer in Archiv f. d.

ges. Phys., Bd. xxv. p. 79 ff.). Successive contrast here is shown in

the fact that a warm sensation appears warmer if a cold one has just

previously been experienced; and a cold one colder, if the preceding

one was warm. If a finger which has been plunged in hot water, and

another which has been in cold water, be both immersed in lukewarm

water, the same water appears cold to the former finger and warm to the

latter. In simultaneous contrast, a sensation of warmth on any part

of the skin tends to induce the sensation of cold in its immediate

neighborhood; and _vice versâ_. This may be seen if we press with the

palm on two metal surfaces of about an inch and a half square and

three-fourths inch apart; the skin between them appears distinctly

warmer. So also a small object of exactly the temperature of the palm

appears warm if a cold object, and cold if a warm object, touch the

skin near it.

[18] Helmholtz, Physiolog. Optik, p. 392.

[19] _Loc. cit._ p. 407.

[20] _Loc. cit._ p. 408.

[21] _Loc. cit._ p. 406.

[22] E. Hering, in Hermann's Handbuch d. Physiologie, iii. 1, p. 565.

[23] Hering: 'Zur Lehre vom Lichtsinne.'--Of these experiments the

following (found on p. 24 ff.) may be cited as a typical one: "From

dark gray paper cut two strips 3-4 cm. long and 1/2 cm. wide, and lay

them on a background of which one half is white and the other half

deep black, in such a way that one strip lies on each side of the

border-line and parallel to it, and at least 1 cm. distant from it.

Fixate 1/2 to 1 minute a point on the border-line between the strips.

One strip appears much brighter than the other. Close and cover the

eyes, and the negative after-image appears.... The difference in

brightness of the strips in the after-image is in general much greater

than it appeared in direct vision.... This difference in brightness

of the strips by no means always increases and decreases with the

difference in brightness of the two halves of the background.... A

phase occurs in which the difference in brightness of the two halves

of the background entirely disappears, and yet both after-images of

the strips are still very clear, one of them brighter and one darker

than the background, which is equally bright on both halves. Here can

no longer be any question of contrast-effect, because the _conditio

sine quâ non_ of contrast, namely, the differing brightness of the

ground, is no longer present. This proves that the different brightness

of the after-images of the strips must have its ground in a different

state of excitation of the corresponding portions of the retina, and

from this follows further that both these portions of the retina

were differently stimulated during the original observation; for the

different after-effect demands here a different fore-effect.... In

the original arrangement, the objectively similar strips appeared of

different brightness, because both corresponding portions of the retina

were truly differently excited."

[24] Helmholtz, Physiolog. Optik, p. 407.

[25] In Archiv f. d. ges. Physiol., Bd. xli. §. 1 ff.

[26] Helmholtz, _loc. cit._ p. 412.

[27] See Hering: Archiv f. d. ges. Physiol., Bd. xli. S. 358 ff.

[28] Hering: Archiv f. d. ges. Physiol., Bd. xl. S. 172 ff.; Delabarre:

American Journal of Psychology, ii. 636.

[29] Hering: Archiv f. d. ges. Physiol., Bd. xli. S. 91 ff.

[30] Die Gesichtsempfindungen u. ihre Analyse, p. 128.

[31] Mr. Delabarre's contribution ends here.

[32] Physiol. Psych., i. 351, 458-60. The full inanity of the law of

relativity is best to be seen in Wundt's treatment, where the great

'_allgemeiner Gesetz der Beziehung_,' invoked to account for Weber's

law as well as for the phenomena of contrast and many other matters,

can only be defined as a tendency _to feel all things in relation to

each other_! Bless its little soul! But why does it change the things

so, when it thus feels them in relation?

[33] Ladd: Physiol. Psych., p. 348.

[34] Mind, x. 567.

[35] Zwangemässige Lichtempfindung durch Schall (Leipzig, 1881).

[36] Pflüger's Archiv, xlii. 154.

[37] Physiological Psychology, 385, 387. See also such passages as that

in Bain; The Senses and the Intellect, pp. 364-6.

[38] "Especially must we avoid all attempts, whether avowed or

concealed, to account for the _spatial_ qualities of the presentations

of sense by merely describing the qualities of the simple sensations

and the modes of their combination. It is position and extension in

space which constitutes the very peculiarity of the objects as _no

longer_ mere sensations or affections of the mind. As sensations, they

are neither _out_ of ourselves nor possessed of the qualities indicated

by the word spread-out." (Ladd, _op. cit._ p. 391.)

[39] A. Riehl: Der Philosophischer Kriticismus, Bd. ii. Theil ii. p. 64.

[40] On Intelligence, part ii. bk. ii. chap. ii. §§ vii, viii. Compare

such statements as these: "The consequence is that when a sensation has

for its usual condition the presence of an object more or less distant

from our bodies, and experience has once made us acquainted with this

distance, we shall situate our sensation at this distance.--This, in

fact, is the case with sensations of hearing and sight. The peripheral

extremity of the acoustic nerve is in the deep-seated chamber of the

ear. That of the optic nerve is in the most inner recess of the eye.

But still, in our present state, we never situate our sensations

of sound or color in these places, but without us, and often at a

considerable distance from us.... All our sensations of color are thus

projected out of our body, and clothe more or less distant objects,

furniture, walls, houses, trees, the sky, and the rest. This is why,

when we afterwards reflect on them, we cease to attribute them to

ourselves; they are alienated and detached from us, so far as to

appear different from us. Projected from the nervous surface in which

we localize the majority of the others, the tie which connected them

to the others and to ourselves is undone.... Thus, all our sensations

are wrongly situated, and the red color is no more extended on the

arm-chair than the sensation of tingling is situated at my fingers'

ends. They are all situated in the sensory centres of the encephalon;

all appear situated elsewhere, and a common law allots to each of them

its apparent situation." (vol. ii. pp. 47-53.)--Similarly Schopenhauer:

"I will now show the same by the sense of sight. The immediate

_datum_ is here limited to the sensation of the retina which, it is

true, admits of considerable diversity, but at bottom reverts to the

impression of light and dark with their shades, and that of colors.

This sensation is through and through subjective, that is, inside of

the organism and under the skin." (Schopenhauer: Satz vom Grunde, p.

58.) This philosopher then enumerates _seriatim_ what the Intellect

does to make the originally subjective sensation objective: 1) it

turns it bottom side up; 2) it reduces its doubleness to singleness;

3) it changes its flatness to solidity; and 4) it projects it to a

distance from the eye. Again: "_Sensations_ are what we call the

impressions on our senses, in so far as they come to our consciousness

as states of our own body, especially of our nervous apparatus; we

call them _perceptions_ when we form out of them the representation

of outer objects." (Helmholtz: Tonempfindungen, 1870, p. 101.)--Once

more: "Sensation is always accomplished in the psychic centres, but

it manifests itself at the excited part of the periphery. In other

words, one is conscious of the phenomenon in the nervous centres,...

but one perceives it in the peripheric organs. This phenomenon depends

on the experience of the sensations themselves, in which there is a

_reflection_ of the subjective phenomenon and a tendency on the part of

perception to return as it were to the external cause which has roused

the mental state because the latter is connected with the former."

(Sergi: Psychologie Physiologique (Paris, 1888), p. 189.)--The clearest

and best passage I know is in Liebmann: Der Objective Anblick (1869),

pp. 67-72, but it is unfortunately too long to quote.

[41] This is proved by Weber's device of causing the head to be firmly

pressed against a support by another person, whereupon the direction of

traction ceases to be perceived.

[42] Lotze: Med. Psych., 428-433; Lipps: Grundtatsachen des

Seelenlebens, 582.

[43] Injuries to Nerves (Philadelphia, 1872), p. 350 ff.

[44] In reality it probably means only a restless movement of desire,

which he might make even after he had become aware of his impotence to

touch the object.

[45] Revue Philosophique, vii. p. 1 ff., an admirable critical article,

in the course of which M. Janet gives a bibliography of the cases in

question. See also Dunan: _ibid._ xxv. 165-7. They are also discussed

and similarly interpreted by T. K. Abbot: Sight and Touch (1864),

chapter x.

[46] The intermediary and shortened locations of the lost hand and

foot in the amputation cases also show this. It is easy to see why the

phantom foot might continue to follow the position of the artificial

one. But I confess that I cannot explain its half way-positions.

[47] It is from this confused assumption that the time-honored riddle

comes, of how, with an upside-down picture on the retina, we can see

things right-side up. Our consciousness is _naïvely_ supposed to

inhabit the picture and to feel the picture's position as related

to other objects of space. But the truth is that the picture is

non-existent either as a habitat or as anything else, for immediate

consciousness. Our notion of it is an enormously late conception. The

outer object is given immediately with all those qualities which later

are named and determined in relation to other sensations. The 'bottom'

of this object is where we see what by touch we afterwards know as our

_feet_, the 'top' is the place in which we see what we know as other

people's heads, etc., etc. Berkeley long ago made this matter perfectly

clear (see his Essay towards a new Theory of Vision, §§ 93-98, 113-118).

[48] For full justification the reader must see the next chapter.

He may object, against the summary account given now, that in a

babe's immediate field of vision the various things which appear are

located _relatively to each other_ from the outset. I admit that _if

discriminated_, they would appear so located. But they are parts of

the content of one sensation, not sensations separately experienced,

such as the text is concerned with. The fully developed 'world,' in

which all our sensations ultimately find location, is nothing but an

imaginary object framed after the pattern of the field of vision, by

the addition and continuation of one sensation upon another in an

orderly and systematic way. In corroboration of my text I must refer

to pp. 57-60 of Riehl's book quoted above on page 32, and to Uphues:

Wahrnehmung und Empfindung (1888), especially the _Einleitung_ and pp.

51-61.

CHAPTER XVIII.

IMAGINATION.

_Sensations, once experienced, modify the nervous organism, so that

copies of them arise again in the mind after the original outward

stimulus is gone._ No mental copy, however, can arise in the mind,

of any kind of sensation which has never been directly excited from

without.

The blind may dream of sights, the deaf of sounds, for years after they

have lost their vision or hearing;[49] but the man _born_ deaf can

never be made to imagine what sound is like, nor can the man _born_

blind ever have a mental vision. In Locke's words, already quoted, "the

mind can frame unto itself no one new simple idea." The originals of

them all must have been given from without. Fantasy, or Imagination,

are the names given to the faculty of reproducing copies of originals

once felt. The imagination is called 'reproductive' when the copies

are literal; 'productive' when elements from different originals are

recombined so as to make new wholes.

_After-images_ belong to sensation rather than to imagination; so that

the most immediate phenomena of imagination would seem to be those

tardier images (due to what the Germans call _Sinnesgedächtniss_) which

were spoken of in Vol. I, p. 617,--coercive hauntings of the mind by

echoes of unusual experiences for hours after the latter have taken

place. The phenomena ordinarily ascribed to imagination, however, are

those mental pictures of possible sensible experiences, to which the

ordinary processes of associative thought give rise.

When represented with surroundings concrete enough to constitute a

_date_, these pictures, when they revive, form _recollections_. We have

already studied the machinery of recollection in Chapter XVI. When the

mental pictures are of data freely combined, and reproducing no past

combination exactly, we have acts of imagination properly so called.

OUR IMAGES ARE USUALLY VAGUE.

For the ordinary 'analytic' psychology, each sensibly discernible

element of the object imagined is represented by its own separate idea,

and the total object is imagined by a 'cluster' or 'gang' of ideas. We

have seen abundant reason to reject this view (see Vol. I, p. 276 ff.).

An imagined object, however complex, is at any one moment thought in

one idea, which is aware of all its qualities together. If I slip into

the ordinary way of talking, and speak of various ideas 'combining,'

the reader will understand that this is only for popularity and

convenience, and he will not construe it into a concession to the

atomistic theory in psychology.

Hume was the hero of the atomistic theory. Not only were ideas copies

of original impressions made on the sense-organs, but they were,

according to him, completely adequate copies, and were all so separate

from each other as to possess no manner of connection. Hume proves

ideas in the imagination to be completely adequate copies, not by

appeal to observation, but by _a priori_ reasoning, as follows:

"The mind cannot form any notion of quantity or quality, without

forming a precise notion of the degrees of each," for "'tis confessed

that no object can appear to the senses; or in other words, that

no impression[50] can become present to the mind, without being

determined in its degrees both of quantity and quality. The confusion

in which impressions are sometimes involved proceeds only from

their faintness and unsteadiness, not from any capacity in the

mind to receive any impression, which in its real existence has no

particular degree nor proportion. That is a contradiction in terms;

and even implies the flattest of all contradictions, _viz._, that

'tis possible for the same thing both to be and not to be. Now since

all ideas are derived from impressions, and are nothing but copies

and representations of them, whatever is true of the one must be

acknowledged concerning the other. Impressions and ideas differ only

in their strength and vivacity. The foregoing conclusion is not

founded on any particular degree of vivacity. It cannot therefore be

affected by any variation in that particular. An idea is a weaker

impression; and as a strong impression must necessarily have a

determinate quantity and quality, the case must be the same with its

copy or representative."[51]

The slightest introspective glance will show to anyone the falsity of

this opinion. Hume surely had images of his own works without seeing

distinctly every word and letter upon the pages which floated before

his mind's eye. His dictum is therefore an exquisite example of the

way in which a man will be blinded by _a priori_ theories to the

most flagrant facts. It is a rather remarkable thing, too, that the

psychologists of Hume's own empiricist school have, as a rule, been

more guilty of this blindness than their opponents. The fundamental

_facts_ of consciousness have been, on the whole, more accurately

reported by the spiritualistic writers. None of Hume's pupils, so far

as I know, until Taine and Huxley, ever took the pains to contradict

the opinion of their master. Prof. Huxley in his brilliant little work

on Hume set the matter straight in the following words:

"When complex impressions or complex ideas are reproduced as memories,

it is probable that the copies never give all the details of the

originals with perfect accuracy, and it is certain that they rarely

do so. No one possesses a memory so good, that if he has only once

observed a natural object, a second inspection does not show him

something that he has forgotten. Almost all, if not all, our memories

are therefore sketches, rather than portraits, of the originals--the

salient features are obvious, while the subordinate characters are

obscure or unrepresented.

"Now, when several complex impressions which are more or less

different from one another--let us say that out of ten impressions

in each, six are the same in all, and four are different from all

the rest--are successively presented to the mind, it is easy to see

what must be the nature of the result. The repetition of the six

similar impressions will strengthen the six corresponding elements of

the complex idea, which will therefore acquire greater vividness;

while the four differing impressions of each will not only acquire no

greater strength than they had at first, but, in accordance with the

law of association, they will all tend to appear at once, and will

thus neutralize one another.

"This mental operation may be rendered comprehensible by considering

what takes place in the formation of compound photographs--when the

images of the faces of six sitters, for example, are each received on

the same photographic plate, for a sixth of the time requisite to take

one portrait. The final result is that all those points in which the

six faces agree are brought out strongly, while all those in which

they differ are left vague; and thus what may be termed a _generic_

portrait of the six, in contradistinction to a _specific_ portrait of

any one, is produced.

"Thus our ideas of single complex impressions are incomplete in one

way, and those of numerous, more or less similar, complex impressions

are incomplete in another way; that is to say, they are _generic_, not

_specific_. And hence it follows that our ideas of the impressions in

question are not, in the strict sense of the word, copies of those

impressions; while, at the same time, they may exist in the mind

independently of language.

"The generic ideas which are formed from several similar, but not

identical, complex experiences are what are called _abstract_ or

_general_ ideas; and Berkeley endeavored to prove that all general

ideas are nothing but particular ideas annexed to a certain term,

which gives them a more extensive signification, and makes them

recall, upon occasion, other individuals which are similar to them.

Hume says that he regards this as 'one of the greatest and the most

valuable discoveries that has been made of late years in the republic

of letters,' and endeavors to confirm it in such a manner that it

shall be 'put beyond all doubt and controversy.'

"I may venture to express a doubt whether he has succeeded in his

object; but the subject is an abstruse one; and I must content myself

with the remark, that though Berkeley's view appears to be largely

applicable to such general ideas as are formed after language has

been acquired, and to all the more abstract sort of conceptions, yet

that general ideas of sensible objects may nevertheless be produced

in the way indicated, and may exist independently of language. In

dreams, one sees houses, trees, and other objects, which are perfectly

recognizable as such, but which remind one of the actual objects as

seen 'out of the corner of the eye,' or of the pictures thrown by a

badly-focussed magic lantern. A man addresses us who is like a figure

seen in twilight; or we travel through countries where every feature

of the scenery is vague; the outlines of the hills are ill-marked, and

the rivers have no defined banks. They are, in short, generic ideas

of many past impressions of men, hills, and rivers. An anatomist who

occupies himself intently with the examination of several specimens

of some new kind of animal, in course of time acquires so vivid a

conception of its form and structure that the idea may take visible

shape and become a sort of waking dream. But the figure which thus

presents itself is generic, not specific. It is no copy of any one

specimen, but, more or less, a mean of the series; and there seems no

reason to doubt that the minds of children before they learn to speak,

and of deaf-mutes, are peopled with similarly generated generic ideas

of sensible objects."[52]

_Are Vague Images 'Abstract Ideas'?_

The only point which I am tempted to criticise in this account is Prof.

Huxley's _identification of these generic images with 'abstract or

general ideas' in the sense of universal conceptions._ Taine gives the

truer view. He writes: