equidistant on the farther disc, and on these were clasped black tin
strips bearing letters or numbers or colors. The nearer disc was
similarly divided and an opening, 3 mm. in width, was cut at each
radius. This exposed the number. A cardboard placed between the discs
limited the range of vision, its opening being 4 × 5 cm.
The figures were 10 mm. high, white, and placed on a dark background.
Preparatory stimuli were given to enable the subject to adjust his
eye to the farther disc. They were so placed as to fall on different
retinal points, thus avoiding fatigue.
Many of the tests employed by Ranschburg were used again to ascertain
the influence of the change in method and with the hope that such
differences might throw some light on the nature of the interference.
At first there were six subjects, afterwards eight--all graduate
students and trained in laboratory work. The experiment was carried
on in the morning. Numbers consisting of six digits were exposed on a
dark background. The time of exposure varied with the subject, but was
constant throughout the experiment. The subject was asked to record
the number immediately after perceiving it, but in almost every case
it was read verbally (its retention being thus facilitated) and then
recorded.
For the first few weeks letters were used. But since subjects found
it very difficult to distinguish these, a change was made to figures.
For a month and a half numbers were given for the purpose of training
the subjects and of ascertaining the speed best adapted to each. This
varied from 5-1/2" to 8" a revolution, each figure being exposed from
115 to 166 sigma.
Three series of numbers were given: (1) Homogeneous, containing a
repeated figure, as, 495851. (2) Heterogeneous; as, 708654. (3)
Similar, that is, in construction; as, 813470 (8 and 3 being easily
substituted for each other). Other similars given by Ranschburg are 9
and 0, 9 and 6, 9 and 2, and 5 and 3.
In order to determine the place of greatest interference, the repeated
figures were located in all possible positions, while the preceding
and succeeding figures were left unaltered, so as to obviate any
new influences which might result from a change of relations. There
are fifteen possible variations of the series: _mabcdm_, _ambcdm_,
_abmcdm_, _abcmdm_, _abcdmm_, etc.
The following table, illustrative of the scheme _ambmcd_, will show the
character of the results obtained. Only the numbers in which errors
occur are here recorded, those figures which were incorrectly perceived
being printed in heavy type. The dash is used when the location of the
figure omitted is known, and the interrogation mark when the reply is
doubtful.
8" 8" 5-1/2" 5-1/2" 5-1/2" 8"
V. R. S. M. H. E.
708025 70625 76082 ..... 70825 7082-5 70285
958564 95584 ..... ..... 95864 985 ? 4 958-54
281845 281485 ..... 20861 28185 281-54
436392 43632 43636 436932 436924 43632 43632
526273 526723 5257 572673 52763 ..... 52623
940469 94069 940465 ..... 94069 94640 940-69
The interference may result in permutation, substitution, or
inhibition. The latter two may take several forms; as, inhibition of
identicals, of similars, of dissimilars, the location of the omitted
figure being known or unknown; also, substitution of an identical,
similar, or dissimilar figure which precedes or follows.
The homogeneous series (540 tests) gives results as follows:
HOMOGENEOUS SERIES
Inhibition of Inhibition of Inhibition
Identicals. Similars. due to Location.
Location
of the Spot Spot Spot Spot Spot Spot
Identicals. Known Unknown Known Unknown Known Unknown
_mabcdm_
1 1=6 1 1 4 5
_ambcdm_
2 2=6 5 2 1 3
3 3=6 2 3 5
4 4=6 3 3 4 2
5 5=6 6 15(?) 4 5
6 1=5 1 2 1 2 1 3
7 2=5 5 3 3
8 3=5 3 7 2 1
9 4=5 2 21(?) 2 5 3
10 1=4 9 4 3
11 2=4 3 9 4 1 7
12 3=4 3 19(?) 1 2 4
13 1=3 [107]5+3(?) 2 1 10
14 2=3 1 11(?) 3 8
15 1=2 6(?) 1 4 9
Total 19 48+75(?) 6 38 17 71
I. _Inhibition_
(1) There is considerable inhibition only when identicals are next to
each other.
(2) There is but little difference in the amount of inhibition when
identicals are removed two and when removed three places.
(3) The interference is greatest when 3d = 4th, 4th = 5th, and 5th =
6th figures, in which schemes it is almost equal in amount.
(4) When identicals are adjacent, it is impossible to decide whether
there be inhibition or fusion, _i. e._, whether one be inhibited and
the other appear, or whether the figure seen be a fusion of the two
(unless there is an omitted figure whose location is known to the
subject). Its intensity does not serve as a clue, for the perception of
the number demands the full concentration of the attention.
II. _Substitution_
When the interference is not sufficiently great to cause inhibition,
substitution may result.
(1) In the majority of cases the substituted figure is a dissimilar not
occurring in the number.
(2) A preceding figure is frequently substituted.
(3) Occasionally a figure is replaced by its similar, but this is not
true of the homogeneous element. (Cf. with Ranschburg.)
(4) Sometimes the next figure in the natural number series is
substituted; as, 9 for 8, 6 for 5.
(5) The figures containing straight lines (4, 7, and especially 1) are
less subject to illusion; likewise the smaller numbers (1, 2, 3, 4).
III. _Permutation_
The permutation represents the least interference.
(1) The 4th and 5th figures are most often exchanged.
(2) The figure is seldom permuted more than two places, and generally
but one.
The recording of the number was most interesting. Generally the
first few figures and the last were written without comment, but the
4th and 5th often called forth an expression of doubt, which was
immediately followed by an exclamation at the coming of the figure into
consciousness as if by "inspiration." The experience was extremely
peculiar. The figure, fully as distinct as those already perceived,
was always from 5″ to 10″ late, and seemed to "pop in unannounced"--to
"come from nowhere." A substitution or permutation occurred without
this lapse of time.
HETEROGENEOUS SERIES
(1) There are less than half as many inhibitions as in the homogeneous
series, the largest number being in the 4th and 5th places.
(2) The number of substitutions is decreased by a fourth, the
identicals and similars remaining the same.
(3) There are no fusions.
(4) Fewer permutations are found in this series. The 4th and 5th
figures are most often permuted. In a very few cases the figure is
permuted four and five places.
(5) There are an equal number of doubtful perceptions in both series.
SIMILAR SERIES
(1) There are few cases of inhibition, and even more surprising is the
small number of cases in which a figure is inhibited by its similar.
(2) There are more substitutions, 6 being very often substituted for
5, generally in the 6th place and when preceded by 0 or 9, often by
both. Similars are never replaced by identicals (69 by 66 or 99) as
Ranschburg found in his experiments.
(3) The fusion of similars equals that of identicals in the homogeneous
series.
(4) The number of permutations is the same as in the homogeneous series
and less than in the heterogeneous.
(5) The doubtful perceptions have decreased by half.
That there are fewer errors in this series than in the homogeneous
or heterogeneous, may be due to the fact that it was given last,
especially since one subject showed marked improvement in the entire
series and another during the last half. These subjects suddenly began
to see six figures, while previously they had seen but five and those
contained errors.
In the above 1620 tests, 9 and 0, and 8 and 3, are sometimes inhibited
by and substituted for each other, but the remaining similars mentioned
by Ranschburg seldom have any such effect.
It is impossible to determine definitely the nature of the
interference, the greatest uncertainty existing in the homogeneous
series when two identicals are adjacent. But the interference is
dependent not only upon the identity or similarity of the figures of
which the number is composed but also upon their location.
INHIBITIONS
1 2 3 4 5 6 Total
Place Place
known unknown K. U. K. U. K. U. K. U. K. U. K. U.
Homogeneous 1 13 2 28 9 41 15 31 15 44 42 157
6(?) 14(?) 19(?) 21(?) 15(?) 75(?)
Heterogeneous 2 5 1 8 2 15 4 36 5 34 2 25 16 123
Similar 4 4 5 3 6 2 13 5 32
Total
excluding(?) 2 5 2 25 4 47 13 82 23 71 19 82 63 312
Total of Known
+ Unknown 7 27 51 95 94 101 375
(?) Inhibition or fusion.
SUBSTITUTIONS
1 2 3 4 5 6 Total
Homogeneous 8 12 26 27 38 14 125
Heterogeneous 4 4 14 21 30 20 93
Similar 1 5 9 25 33 27 100
Total 13 21 49 73 101 61 318
FUSIONS [See (?) under Inhibitions]
1 2 3 4 5 6 Total
Homogeneous 1 2 1 3 10 17
Heterogeneous 0 0 0 0
Similar 3 3 6 6 18
Total 1 5 4 9 16 35
Note. There were no clear cases of fusion, but the evidence favored
fusion rather than inhibition.
PERMUTATIONS
1 2 3 4 5 6 Total
Homogeneous (a) 6 29 46 56 30 167
(b) 5 21 45 68 35 174
Heterogeneous (a) 15 25 60 62 28 190
(b) 14 23 51 82 44 214
Similar (a) 13 20 37 78 16 164
(b) 12 17 26 75 28 158
Total (a) 34 74 143 196 74 521
(b) 31 61 122 225 107 546
(a) forward, (b) backward
Note. The permutation of an inhibited figure was not noted unless its
location was known: hence the difference in the number of forward and
backward permutations.
1 2 3 4 5 6 Total
Total Interferences 54 160 323 509 524 300 1870
% 3% 9% 17% 27% 28% 16%
Absolute Errors
(excluding 20 55 119 191 225 103 713
Permutations) 3% 8% 17% 27% 31% 14%
ABSOLUTE ERRORS (excluding Permutations)
Homogeneous Heterogeneous Similar
Inhibitions 199 139 37
Substitutions 129 93 101
Fusions 17 18
(?) 75
Total 420 232 156
52% 29% 19%
Over 50% of the errors were found in the 4th and 5th places.
[Ranschburg: 90% of errors in right half--60% in 5th place, 30% in 4th,
few in 6th.]
In 1620 tests, the homogeneous series contained 52% of the absolute
errors, the heterogeneous 29%, and the similar 19%.
COLORS
In the hope that some light might be thrown upon the main question at
issue, the writer changed the stimuli, using colors instead of numbers.
It was important that the colors should be of the same or only slightly
varying intensity and that they should be easily distinguishable. In a
series of preliminary experiments in which red, blue, yellow, green,
brown, gray, pink, and violet were used, red was lost in 8% of the
tests, and gray in 25%.
Colors 1×4 cm. in size "ran into each other," while those which were
1×1 cm. remained distinct.
Here it was found necessary to distinguish between the various
factors which might cause inhibition. Three factors entered into each
test--perceiving, naming, remembering.
Four subjects found difficulty in naming, especially at first. The
various methods of naming are given below in detail. M. says: "The name
of the color is localized in my mouth. Generally there is no movement
of the tongue--an impulse only; and the name is felt in that part of
the mouth where the sound would be reflected, as, red in the upper
part, blue near the front, etc."
S.: "Usually there is no apparent tendency to pronounce. Occasionally,
naming them over inaudibly before recording is found advantageous."
E., V., and H.: "The naming is mental, but is accompanied by a slight
movement of the tongue and throat."
684 heterogeneous and 200 homogeneous tests showed that greatest
inhibition occurred in the following order: 4th place (27%), 3d
(26%), 5th (24%), 2d (11%), 6th (8%), 1st (4%). There was but little
difference in the 3d, 4th, and 5th places.
During first tests subjects were allowed only one exposure, but later
it was thought best to eliminate all omissions resulting from inability
to name colors perceived, and hence they were asked to record only when
able to name all colors perceived during that exposure. However several
required but one exposure.
Preliminary drill was given for two weeks. Since no clear cases of
fusion had been obtained in the entire number-series, the one aim
of the experimenter was to ascertain whether fusion of colors, even
though of heterogeneous, be possible. Eight hundred heterogeneous
tests gave 927 cases of inhibition, 7 of fusion, and 18 which, though
somewhat doubtful, yet gave more evidence of fusion than of inhibition.
Yellow (3d place) and brown (6th place) were seen as yellowish-brown,
brown and pink as pinkish-brown, etc. Gray was seen several times
instead of a color and its complementary when these were in immediate
succession. This was true of both red and blue. Half of the total
number of substitutions was due to the displacement of yellow by brown.
And a color not in the series was as likely to be substituted as one
preceding or following the displaced color.
Two hundred and fifty-two homogeneous tests showed that there is
greatest interference when identicals are in immediate succession, and
least, when removed two places. The doubtful (fusion?) cases number
_one third_ of the inhibited. The 4th and 5th colors are permuted most
often, as was found to be the case in the heterogeneous series also.
The element is generally permuted but one place.
The heterogeneous color-tests show three times as much interference as
the corresponding number-tests, and the homogeneous twice as much. The
discrepancy in the amount of variation may be due to the experiments
with the heterogeneous colors being earlier, when naturally more errors
would be made.
However, a comparison of 252 homogeneous with the same number of
heterogeneous tests, taken at the same time, shows that there is
a much larger difference in the number of absolute errors between
the heterogeneous and the homogeneous number-series than there is,
proportionately, between the two series of color-tests.
Lest the want of correspondence in the results might have been due to
the comparatively small number of immediately successive identicals in
the color-tests, 90 homogeneous tests, equally distributed among all
possible variations in the location of the identical elements, were
compared with 90 heterogeneous, and it was unexpectedly found that the
absolute errors as well as the permutations were almost equal in the
two series. Nevertheless, the validity of a conclusion based on so few
tests may well be questioned.
Ranschburg found that simultaneous homogeneous stimuli interfere with
one another; while simultaneous heterogeneous stimuli clear the way for
one another. On the basis of the experiments with numbers, the writer
would amend the conclusion reached in the earlier research to read
thus: Homogeneous optical stimuli, whether occurring simultaneously in
different positions, or in immediate succession in the same positions,
interfere with one another; while heterogeneous stimuli clear the way
for one another.
FOOTNOTES:
[Footnote 106: Ranschburg: Zeitschrift für Psychologie, vol. 30, 1902.]
[Footnote 107: Fusion or inhibition?]
SUBJECTIVE AND OBJECTIVE SIMULTANEITY
BY THOMAS H. HAINES
This investigation finds its starting-points in two widely separated
lines of experimentation in the problems of attention. These two lines
are the "scope-of-attention" experiment with the tachistoscope, and the
"time-displacement" experiment with the pendulum apparatus. It seems
to me these two can be brought into relation to each other to the help
of each of them individually, and that an investigation taking these
wide relations within its scope may reasonably be expected to throw
new light upon the manner in which mental processes are related to
each other when they are together in consciousness at the same time.
The first of these experiments (tachistoscopic) is concerned with the
number and relative clearness of the processes which go on at the same
time. The second (displacement) is concerned with the conditions of
the subjective displacement of one of two objectively simultaneous
stimuli with reference to the other. Its problem is the essential
psychological problem involved in the astronomer's error in transit
observations by the eye-and-ear method, for the personal equation
arising in these observations is more a matter of the reciprocal
relations among the processes which are together in consciousness at
the moment of observation than it is of mere reaction time. It is
primarily more a matter of relative clearness, as controlled probably
through interference of one with another, than it is of the more or
less temperamental facility of converting ideas into action.
The psychological question at the heart of the observation-error,
called the personal equation, is this,--What are the conditions which
hinder such a division of attention among the parts of the complex
operation of coördinating sense-stimulations, that the processes
which start simultaneously may proceed to equal clearness at the
same time, and so be perceived as simultaneous? The facts sought in
order to answer this question are the very same as some of those,
at least, demanded by the "scope-of-attention" investigation when
it really opens up to its true problem. W. Wirth[108] has recently
shown, in an exhaustive criticism of the tachistoscopic method, that
"scope of attention" is primarily concerned with the _relations_ of
the processes present together, and that this demands a previous
exhaustive study of their _relative clearnesses_. Earlier studies by
the tachistoscopic method, as, for example those of Cattell[109] on
the relatively short time for the perception of letters in words,
as compared with that for separate letters, and the overlapping of
processes in continuous reading, showed that the important question is,
_what_ are the processes which may go on at the same time. Leaving out
a statement of the nature of the processes is equivalent to leaving
out one of the dimensions when endeavoring to state the contents of
a solid. The scope of attention can be defined adequately only when
one knows fully _what_ the separate processes are as well as _how
many_ there are. This analysis, which the scope-of-attention problem
demands, cannot fail to be directly fruitful for the solution of the
time-displacement problem. The analysis of this larger problem directly
involves the former. Any attempt to investigate the time-displacement
of sense-impressions from simultaneous stimuli must inevitably place
the highest value upon the whole detailed analysis of any moment of
attentive effort.
The present investigation, starting with the facts of
time-displacement, and taking the hint offered by Gonnessiat,[110]
attempts to show, by a more complete analysis, the effects of the
various relations within each series,--the visual within which the
sounds are to be placed, and the auditory series itself, and also
relations existing between the two series. In other words, the
attempt is made to strip the "displacement" experiment until nothing
more remains to be coördinated than a single pair of simultaneous
stimuli. This was the experiment of Exner.[111] He investigated
the shortest discriminable interval marked off by various pairs of
stimuli, addressed to the same sense and to different senses. From this
coördination of a visual and an auditory stimulus, where the limits
of the "specious present" are obtained, I make a turn into the realm
of the scope of attention. By a new method, whereby impairment of
accuracy of processes is made the test as to whether the processes have
proceeded together, it is shown that two such perceptual processes can
go on just about as well at the same time as separately. Since this
test is subject to the objection that the visual and auditory processes
may really be successive, though seemingly at the same time, owing to
retinal inertia, the same question is removed to an entirely different
plane in a further and more detailed set of experiments where the
processes combined are _judgments of comparison_ based upon one and the
same visual sensation.
EXPERIMENTS IN TIME-DISPLACEMENT
The Leipsic Complication Experiment with the pendulum apparatus (for
description of this see Wundt's Physiol. Psy., 5th ed., vol. 3, p. 82)
was an early adaptation of the astronomers' eye-and-ear method to the
purposes of psychological experimentation. Instead of localizing a
visual stimulus (star on meridian) in an auditory series (clicks of a
chronoscope) as in the eye-and-ear method, this adaptation localized
an auditory stimulus (bell-stroke) in a visual series (successive
positions of a pointer on a graduated circle). This pointer passed
around to the right and to the left from the position of rest, in
which it pointed vertically upward, as the pendulum, to which it was
connected by clockwork, swung back and forth. By a simple adjustment
the bell-stroke could be made to come at any point in the complete
double swing of the pendulum, and so anywhere in the arc over which
the pointer moved. This machine makes an additional problem as to the
effects upon displacement of the increasing and decreasing speed. My
aim being to simplify as much as possible the displacement-error and
so reduce it to its elements, this feature was not only not of direct
interest, but it was very desirable to dispense with it altogether.
This was done by arranging the visual series so that the members were
shown in perfectly regular order, _i. e._ with equal time-intervals,
throughout the series. These equal intervals were secured by the
rotation of a disc at a uniform rate.
My method also gave a more distinctly serial character to the visual
stimuli, in that they were separated by blank periods. The series
consisted of letters in alphabetical order. Denison's smallest white
letters, about six millimetres in height, were pasted upon a disc of
black cardboard, near the circumference and perpendicular to radii, so
that they would appear in succession and right side up, to an observer
looking through a slit at the peripheral region of the disc, as it
rotated. The letters were placed in three concentric rows, so that as
the disc rotated they appeared in three different places. The disc was
56.5 cm. in diameter. As a further aid in securing separate exhibitions
of letters, another black disc of the same size as the one bearing
the letters, with radial slits 2 mm. wide and cut in from the edge 4
cm., opposite each letter on the other disc, was mounted on the same
shaft, six inches from the first, and between it and the observer. A
short observation-tube was placed at the same height as the axis of the
discs parallel to this axis, and opposite the slits when they were at
this elevation. Looking through this, as the discs were rotated, one
would see the letters right side up and in serial succession. Uniform
illumination was secured by working in a dark room with artificial
light. An electric lamp was hung between the discs. Uniform motion was
secured by an automatic control gravity motor, connected by belt with a
pulley on the disc-shaft.
The auditory stimulus, a click, adjustable to any part of the series,
was made as follows: A wooden shaft, mounted on the same axle as the
discs, and beyond the discs from the observer, could be rotated freely
around the axle when the nut securing it was loosened. This shaft
extended beyond the edge of the disc. It carried a copper wire which
was in contact with the axle. A mercury cup was placed on the table,
upon which the machine rested, in such position that the copper tip
passed through the mercury when the discs rotated. It was thus a very
simple matter to connect an electric sounder so that it would click
every time the circuit was made by the copper passing through the
mercury. And, by the adjustment of the wooden shaft, the click was
readily placed anywhere in the visual series.
As already suggested above, the length of interval between members
of the visual series, and also the time between clicks, seem to be
important factors in determining the amount, and perhaps also the
direction of the displacement. Bessel found his personal equation was
considerably diminished when he used a clock marking half-seconds
instead of one marking seconds. Wolf also diminished his error by using
a clock beating one hundred times a minute instead of one beating
seconds, which he was accustomed to use. Wundt found his customary
negative displacement on the pendulum apparatus (coördinating the
sound with a position of the index earlier than that with which it
was actually simultaneous) disappeared when he had members of the
visual series one thirty-sixth second apart and the auditory stimuli
one second apart. It seemed important at the outset, therefore, to
determine, if possible, the effects of each of these factors.
BOTH INTERVALS PROGRESSIVELY VARIED
In each experiment the observer was allowed to observe as many
complications (coincidences of click and letter) as he desired, in
order to assure himself of his judgment. The experimenter counted and
recorded the number observed in each experiment. Experiments were made
in series of ten. Six different combinations of intervals were used in
this first group of experiments. The auditory intervals (time between
successive clicks) and visual intervals (time between successive
members of the visual series) are given at the tops of the columns in
Table I. This table is a summary presentation of the results of this
group. There were three observers. During each hour of experimentation
with a given observer, at least one series with each of the first four
time-interval combinations was tried out. "Aver. num. Trials" means
the average number of complications observed in the whole number of
tests averaged. "Num. Series av." means the number of series of ten
experiments each averaged to give the displacement results below.
"Aver. Error" is the average of all the displacements of the auditory
impression, _irrespective of the direction of the displacement_. "Mean
Displacement" is the _actual mean displacement_ as obtained by dividing
the algebraic sum of all displacements, positive and negative, by the
number of experiments. The plus sign indicates a positive displacement,
and the minus sign, a negative. Negative and positive are here used in
the sense customary in similar experiments,--namely, the click, being
heard as simultaneous with a visual impression which actually came
before it, was said to be displaced negatively, and the click, being
heard as simultaneous with a visual impression coming in fact later
than it did, was said to be displaced positively. Average errors and
mean displacements are given in the table in thousandths of seconds.
Observers were asked to locate the click in the visual series in terms
of one tenth the distance or time between the letters.
TABLE I
Aud. Interval (sec.) 1.28 2.56 4.04 8.40 1.28 2.02
Vis. Interval (sec.) .040 .080 .120 .260 .080 .120
Obs.
B Av. num. Trials 13.9 5.8 3.8 2.1 9.8 13.9
Num. Series av. 8 13 13 8 2 2
Aver. Error (sec.) .056 .064 .077 .164´ .045 .067
Mean Displac'mt (sec.) +.045 -.040 -.067 -.152 +.045 +.067
Bo Av. num. Trials 9.4 4.1 3.0 2.0 5.5 3.5
Num Series av. 6 10 11 8 3 2
Aver. Error. (sec.) .114 .060 .054 .049 .05 .082
Mean Displac'mt (sec.) +.114 +.045 +.033 .000 +.045 +.082
M Av. num. Trials 6.3 3.1 2.5 2.2 5.3 4.4
Num. Series av. 9 12 12 10 3 2
Aver. Error (sec.) .09 .07 .076 .110 .067 .172
Mean Displac'mt (sec.) +.089 -.058´ -.058 -.104 +.062 +.168
The first four combinations of intervals above, with which the major
part of the results was obtained, it will be noticed, are approximately
proportionate increases in each interval, column by column. These
conditions were planned with a view to revealing the conditions, most
favorable for coördinating the auditory and visual impressions, for
each observer, so that his displacement would disappear, or show a
tendency to disappear. So far as is shown by these results, there
are here two types of observer. Bo has no mean displacement for the
8.40-.260 sec. combination, and it steadily decreases toward this
point as the two intervals increase. Both B and M, on the other hand,
have a considerable positive mean displacement for the 1.28-.040 sec.
combination, and a considerable negative mean displacement for the
2.56-.080 sec. combination, and there is a further increase in the
negative displacement as the intervals increase from this point. It
seems as though these observers would give a mean displacement of zero
for some combination of intervals between these first two. It will be
noticed that the average number of trials is exceptionally large for
all three of the observers in the first combination. This seemed to
be pretty clearly due to the very short interval separating visual
impressions.
THE AUDITORY INTERVAL _alone_ VARYING
In order more certainly to isolate the influence of the time-interval
between successive auditory impressions, another series of experiments
was performed, in which this interval between clicks, alone, was
varied from series to series. The visual interval was kept at .083
sec. throughout. This seemed to be about the shortest time-separation
at which the successive impressions were perfectly distinct. The
auditory impressions were at 1, 1-1/2, 2, 3, and 4 sec. intervals.
The additional observer, H, was myself. I obtained these results by
experimenting alone. I adjusted the wooden shaft carelessly to a new
position and started the machine. When speed was attained, I would
make the observation just as an observer for whom the adjustment had
been made. I would have as little idea beforehand as he with regard to
the position of the click in the series of letters. Having made the
observation, however, I measured the actual place of the sound and
recorded it, as well as my judgment. In this way, of course, I had some
idea, all the time, as to what kind of displacements I was making and
how large. I was as careless of this knowledge as possible, and the
records were laid aside absolutely, until I was through with the whole
experiment. Terms used in Table II are the same as in Table I.
TABLE II
Aud. Interval (sec.) 1 1-1/2 2 3 4
Vis. Interval (sec.) .083 .083 .083 .083 .083
Obs.
B Av. num. Trials 8.5 6.8 6.2 4.8 4.8
Num. Series av. 10 10 10 10 10
Aver. Error (sec.) .097 .108 .106 .097 .101
Mean Displacement (sec.) +.097 +.108 +.106 +.097 +.101
Bo Av. num. Trials 6.0 5.0 4.2 3.2 3.1
Num. Series av. 10 10 10 10 10
Aver. Error (sec.) .103 .080 .081 .092 .082
Mean Displacement (sec.) +.102 +.073 +.078 +.089 +.075
M Av. num. Trials 4.4 3.8 3.4 3.0 2.8
Num. Series av. 10 10 10 10 10
Aver. Error (sec.) .088 .084 .081 .068 .052
Mean Displacement (sec.) +.086 +.079 +.072 +.051 +.048
H Av. num. Trials
Num. Series av. 10 10 10 10 10
Aver. Error (sec.) .043 .036 .047 .040 .037
Mean Displacement (sec.) -.022 -.012 -.027 -.017 -.013
One series of ten of each of these combinations was given during each
hour of experimentation with each observer. These were also given
in a different order each day, so that no combination should have
the advantage, by practice or lack of fatigue, in the average of the
ten series. Here again it was evident, in the records of each of the
observers for whom the count was made, that the largest number of
trials was necessary in the 1-.083 sec. combination. It thus appears
that it was not the short visual interval, .040, in Table I, that was
responsible for the large number of trials necessary in the first
combination. Here, where there is the same visual interval of .083
sec. throughout, it must be the short auditory interval which makes
particularly difficult conditions for attention. This agreement between
the results in both groups of experiments seems to indicate unfavorable
conditions for accurate coördination at auditory intervals as short
as one second. The large changes in the mean displacement for B and M
between the first two combinations in the first group (Table I) was
kept especially in mind in planning this second series of combined
intervals. It was presumed from the results given by these observers
in Table I that they would each, with the range of auditory interval
presented them in these experiments, show a point of no displacement,
or a very slight one, and an increasing displacement on each side of
this point. They both seemed to indicate a time-interval favorable
for the "ripening of apperception" as Wundt and Von Tschisch call
it, and I planned these experiments especially to bring it out more
clearly. But there is far less indication of a time most favorable for
"ripening" than in the previous group of experiments. B and M both give
all mean displacements as positive, and decidedly small differences in
displacement for the various combinations. Results of Bo are, however,
entirely consistent with those of Table I. H gives a very small
negative mean displacement throughout. This, as well as the smallness
of the average error, may be due to the knowledge of results which I
had.
An examination of the detailed daily results, which cannot be exhibited
here, shows considerable change in the direction of the displacements
as the work proceeded. This is especially marked in the case of B,
who, during the first two hours of experimentation, gave only negative
displacements. Through the rest of the first group there was a gradual
increase of positive displacements, and in the last two hours about 90%
were positive. In the second group he did not give a single negative
displacement. The same change is manifested in the results of M for
the first group; but he did not change over nearly so completely.
In the five hundred experiments of Table II, for M, there are three
hundred and ninety-two positive, sixty-seven negative, and forty-one
_no_ displacements. Bo gave a number of positive displacements from the
start. These increased considerably in the second over the first group,
showing only thirty-seven negative displacements in the second group.
This change in the direction of the displacement, rather independently
of the intervals, is an interference with the main purpose of the
experiment. It may represent the effect of practice.
Angell and Pierce[112] found the same progressive change from negative
to positive displacements. They explained it as a change in the focus
of attention. The visual series is focal at first, and the sound
becomes focal in later experiments. Negative displacements result from
fixing the last possible point in the visual series before the sound
is heard, while positive displacements result from getting the first
letter possible after the sound. The method of my observers, with
the large numbers of trials at their disposal, was to "let the sound
_announce_ the letter" on the first trial, and then to "lie in wait for
the letter" so announced, and to "see whether it was too late or too
early." It was found to be too late usually, for this was the second
method of Angell and Pierce, which gave positive displacements.
So at the next trial the preceding letter would be waited for, and
tested in the same way. The first trial was thus auditory-visual
attention and the second was visual-auditory, and there was a striving
after a balance where neither auditory nor visual impression had the
preference.
As soon as adjustment to the conditions of a given combination had
been secured, it was a simple matter to anticipate, with a fair degree
of accuracy, both a given letter and the recurrence of the sound. The
attention could thus be pretty accurately divided between the two, and
a very small time-displacement was the result. When I was acting as
observer, a change of the auditory interval _upset_ the whole _plan_ of
procedure for a short time. I had to accustom myself to the new rhythm.
But as soon as this adjustment was made, it was just as easy to make
the judgment at one rate as at another, barring variations which might
be called fortuitous, since they were so small. This experience with
the conditions here under consideration, as well as the introspections
of the other observers, convinces me that the conception of an
apperception-ripening time has been overworked.
It is true that I find here, just as Pflaum[113] found, displacements
in both directions with every observer. It seems very doubtful to me,
however, whether these are in any sense due to what may be considered
a fixed apperception-time for a given observer, under fixed objective
conditions. The facility with which adaptation is made to the changed
conditions of a new combination of intervals, so that just as small
displacements are made under one as another, indicates to my mind that
one can control the conditions so that the apperception shall ripen
quickly or slowly, depending upon the warmth of the interest, and the
concentration or division of the attention,--that there is a capacity
in the ordinary individual so to adapt himself to the conditions as to
do equally good work in coördinating two sense-impressions anywhere
within a wide range of intervals. The influence of the length of the
interval separating succeeding clicks, in determining displacements,
has been considerably overestimated. I should state here that no
one of the three observers had any specific training to reduce the
displacement. The results were not discussed with them. They had no
means of knowing what displacements they were making. This certainly
adds strength to the inference, from these results, that there are
adaptable apperceptive conditions for coördinating sense-impressions.
THE INFLUENCE OF THE LENGTH OF THE SERIES OF VISUAL IMPRESSIONS
The next step in the analysis of the complication experiment, bringing
it into relation with the simple coördination of two disparate stimuli,
is to show, if possible, the influence of the _series_ of _visual_
impressions. This naturally divides into two lines, namely, (1) the
_length_ of the series as such, and (2) the relative influence, in
case of a given kind of displacement, of the part of the series coming
_after_ the auditory stimulus, and the part _preceding_ it. For the
first, I used in comparison, a series of twelve letters, a series
of three, and a single letter. For the second, the letter, whose
coördination with the click was set as the task of the observer, was
made successively the first, the last, and the middle member of a
series of five letters.
During each hour of experimentation, the observer was tested as to
his accuracy of localization of the click, (1) in a series of twelve
letters at intervals of .083 sec., (2) in a series of three at the
same interval, and (3) with reference to a single letter. The method
for the first two was exactly as in the preceding experiments. In the
case of the single letter, he was asked to localize as accurately as
possible in terms of the intervals as he remembered them from the
series. This introduced an element of uncertainty. One observer, St,
would not give any judgments as to time-differences in the case of the
single letter. Another method had to be adopted in order to obtain more
comparable results. These results (Table III) are presented as showing,
by comparison with the following table, the transition from one method
to the other. Clicks were at 2-sec. intervals. Each number in the
table is the average result of fifty or more experiments. They are in
thousandths of seconds, and the plus and minus signs indicate positive
and negative displacements.
TABLE III
_Observer_ _Twelve Letters_ _Three Letters_ _One Letter._
A +.012 sec. -.029 sec. -.010 sec.
G -.022 sec. +.004 sec. -.004 sec.
Sh +.028 sec. -.079 sec. -.057 sec.
St -.050 sec. -.036 sec.
Bo +.029 sec. -.015 sec. -.022 sec.
The method of right and wrong cases was used in the next group of
experiments, to secure the same conditions of making the judgment in
each of the three cases used above. Selecting a letter near the middle
of each series, I asked the observer, in each of these cases, just as
in that of the single letter, to say whether the click was before,
on, or after the letter. I worked _out_, in successive experiments by
successive adjustments, from the position of apparent simultaneity
of click and letter, in both directions, to a point where in 75% of
the cases the click seemed to come before; and also to one where it
seemed to come after, in 75% of the cases. So also I worked _in_ both
ways, by successive adjustments, from regions of clear discrimination
of time-difference and direction, to points where the time-relation
was uncertain or wrong in 75% of the trials. By averaging the just
perceptible and the just not perceptible, in each case, the thresholds
were obtained for "click first" and "click last." The time between
these thresholds I call the "range." It is really a measure of James's
"specious present" and of Stern's "Präsenzzeit." (An admirable
presentation of similar results by Wilhelm Peters[114] has appeared
since this work was done.) The best means of comparing these results,
for our present purposes, and also of bringing them into relation with
the complication-results already obtained, is to take the mean point
between these thresholds, and state its position, in time, relative to
the time of the visual stimulus (letter) just before or after which
the click came. This mean point is called the "Threshold Mean" in the
following tables. In Table IV, for example, "After Letter .026 sec."
means that the mean point between the thresholds, "click first" and
"click last" falls twenty-six sigmas after the time of the exposure of
the letter. These results are readily comparable with those of Peters.
By dividing the "range" by two, and adding the "threshold mean" to one
half, and subtracting it from the other, one has the total interval
between "click first" and "click last" and its place with reference to
the time of the visual stimulus.
TABLE IV
_Obs._ _Twelve Letters_ _Three Letters_ _One Letter_
A Threshold Mean After After
Letter .026 sec. On Letter .041 sec. Letter .020 sec.
Range .093 sec. .062 sec.
G Threshold Mean Before Before After
Letter .015 sec. Letter .020 sec. Letter .062 sec.
Range .072 sec. .083 sec. .304 sec.
Sh Threshold Mean Before After After
Letter .003 sec. Letter .027 sec. Letter .003 sec.
Range .172 sec. .111 sec. .241 sec.
It must be distinctly understood that these "threshold means" are
not displacements, and that the two cannot be compared as if they
were statements of the same facts. These _means_ indicate the centre
of gravity of the "click first" "click last" interval with respect to
the visual stimulus. Changes in this centre of gravity may reasonably
be expected to approximate a variation _inverse_ to that of the
displacements of the auditory stimulus. For example, any change in the
conditions which would tend to increase a _negative_ displacement would
tend also to put the centre of gravity of the "click first" "click
last" interval _after_ the visual stimulus, or, if it were already
after, to increase its time after. So also the _positive_ displacement
and the position of the threshold mean _before_ the visual stimulus may
be considered similar indications. For a click given at the time of the
threshold mean of a given observer, in connection with the same visual
stimulus, would certainly be judged by that observer as simultaneous
with the visual stimulus. If, then, this mean is before the visual
stimulus, the sound will be displaced positively, _i. e._, coördinated
with a visual stimulus coming later. If the mean is after the visual
stimulus, the sound will be displaced negatively, _i. e._, coördinated
with a visual stimulus coming earlier. The position of the mean of the
thresholds indicates a tendency toward the displacement of the auditory
impression in the opposite direction.
In Table III, three out of five observers, A, Sh, and Bo, show a change
from a negative displacement in the series of three to a positive
displacement in the series of twelve. If this were the effect of the
series, the same should show in the series of three as compared with
the single letter. Such a change is manifest in the results of Bo. It
is, however, very slight. The others increase the negative displacement
from the single letter to three letters. In Table IV, of the same three
observers represented, Sh changes the threshold mean from _after_ in
the three-letter series to _before_ in the twelve-letter series, and
A changes from _after_ in one letter to _on_ in three letters. These
changes correspond to changes from negative to positive displacements
for increase of series and introduction of series. G shows the same
change from one letter to three, in both tables. These changes, in
55% of the cases offered for comparison in the two tables, indicate
a _decrease_ of _negative displacement_ and an _introduction_ of
_positive displacement_ as the _effect_ of the _visual series_. The
visual element is made more focal in expectant attention as it is
more isolated, and so the tendency toward negative displacement and
increasing negative displacement as the serial character of the visual
impressions is stripped off. But there are strong counteractive
tendencies, which control the 45% of comparisons not mentioned above,
where the increasing series shows increasing negative displacement.
In the series all the observers adopted the method which has been
outlined above, that of letting the click pick out the letter, or
letting the letter announce itself. One said "the letter hits the
sound." After this sorting-out of the letter, they resorted to the
system of tests and counter-tests, in succeeding trials, to correct
the first impression. One can readily understand, then, that when
they were taken off the series altogether, an entirely different
kind of adjustment had to be made. G did not succeed in making this
new adjustment very well, as is shown by his exceptionally large
range under one letter. He could not get the two impressions to come
together. In attending to either one, he could not get the other in
relation to it. There was something in the visual series which enabled
him to get the visual impression in line with the auditory, and when
this was absent the same kind of work could not be done.
St had also a peculiar method, which was directly dependent upon the
serial character of the visual stimuli and impressions. He allowed the
series of clicks and the series of visual impressions to establish
themselves as a complex rhythm. Each series was rhythmic independently.
The two got connection by means of the click appearing as an
"after-strike," as on the piano, to a member of the visual series.
The letter "flashes out" for him as that of which the click was the
"after-strike." The click was thus between two letters. But there was
no amount of before or after about it. It was a general quality of the
whole complex which was taken to mean such and such a position of click
in the series. What he thus translated into temporal judgments, were
qualitative aspects of the rhythmic experience, to which he usually
attached no temporal meaning whatever. Learning how so to translate
them into temporal terms was a definite process of training for him.
Under these circumstances, he of course had an entirely new lesson to
learn when the visual series was taken away. In fact, it might be, he
would now find no visual impression to which the click could be an
after-strike, and so he would be entirely without material to translate
into temporal terms.
Under these circumstances it is not surprising to find G and St
exceptions to the majority of the observers in this experiment. This
makes more probable the effect of the series, inferred above for the
other observers,--namely, series decreases negative displacement.
THE INFLUENCE OF THE _Position_ OF THE _Series_ OF _Visual_
IMPRESSIONS
It was noticed in the series of the three letters, particularly, that
some observers were much more accurate in their work when the click was
near one end of the series. In this experimental group, the comparison
is between cases where the click is coördinated with (1) the first
member of a visual series of five, (2) the middle member of a series
of five, and (3) the last of such a series. The method was the same as
that used in obtaining the results of Table IV. H was the letter used
in each case for coördination. Results follow in Table V.
TABLE V
_Obs._ _H first_ _H middle_ _H last_
A Threshold Mean After Letter After Letter After Letter
.010 (sec.) .021 (sec.) .025 (sec.)
Range .072 (sec.) .085 (sec.) .093 (sec.)
G Threshold Mean Before Letter On Letter Before Letter
.007 (sec.) .007 (sec.)
Range .124 (sec.) .083 (sec.) .151 (sec.)
R Threshold Mean After Letter After Letter After Letter
.032 (sec.) .016 (sec.) .042 (sec.)
Range .464 (sec.) .398 (sec.) .369 (sec.)
Sh Threshold Mean After Letter After Letter After Letter
.025 (sec.) .015 (sec.) .030 (sec.)
Range (sec.) .176 .176 .166
St Threshold Mean After Letter After Letter After Letter
.050 (sec.) .062 (sec.) .078 (sec.)
Range (sec.) .140 (sec.) .108 (sec.) .108 (sec.)
Under these conditions, whatever the effect of the visual series, if
it has any effect, opposite tendencies in direction of displacement
ought to be shown in the "H last" from those in the "H first," results,
as each is contrasted with "H middle." Contrasted in this way, these
results, for A and St, show a relative approach of the mean to zero
for "H first," and a relative departure from zero for "H last," or a
_decrease of a negative displacement for "H first"_ and an _increase
of the same for "H last."_ In other words, the series draws the
displacement of the click toward itself. A _negative displacement is
increased by a series coming before the visual stimulus_ in question,
and _decreased by such a series coming after_. For R and Sh, the
negative displacement is increased in both H first and H last as
compared with H middle, but relatively the most for H last in both
observers. For G there is the same positive displacement introduced
by both H first and H last, but it is less than in any of the other
cases. The drift of the evidence here, then, is that the _visual series
draws the displacement in its own direction_. Each observer who has a
negative displacement (Threshold mean after) with "H middle" increases
this when the series all comes before (H last) and two decrease it
when the series comes after (H first).
THE EFFECT OF RHYTHM (_Repetition of Auditory and of Both Stimuli_)
It is very evident to any one who has worked at all in the complication
experiment, that rhythm plays an important part in the displacement.
Witness also the astronomers' experience cited above, St's waiting
for the rhythm to establish itself, and my own readjustment to the
new conditions when a new combination of intervals was given in the
experiment with varying auditory intervals. In order to show the part
played by rhythm, I tested each one of five observers on several
different days, to fix for each of them both the "click first" and
the "click last" thresholds, as above, under each of the following
conditions: (1) one visual (single letter) and one auditory stimulus
(one pair), (2) one visual (single letter) and many auditory stimuli,
and (3) many visual (single letter repeated) and many auditory stimuli
(many pairs). For visual fixation, the observer had a very dim light at
the end of the observation-tube. The visual stimulus was a flash of red
in the place thus fixated. It had a total duration of less than .005
sec. The surface exposed subtended a vertical visual angle of about
seven tenths of a degree. In the case of one visual and many auditory
stimuli, the visual stimulus was given when the observer had heard the
recurring auditory stimuli several times and had himself given the
"ready" signal. The results follow in Table VI.
TABLE VI
_Obs._ _One Visual and_
_One Pair_ _Many Auditory_ _Many Pairs_
A Threshold
Mean After
Letter (sec.) .005 After Letter .022 After Letter .042
Range (sec.) .021 .024 .039
G Threshold
Mean After
Letter (sec.) .022 After Letter .009 After Letter .005
Range (sec.) .078 .083 .084
H Threshold
Mean Before
Letter (sec.) .011 After Letter .006 After Letter .012
Range (sec.) .035 .035 .039
Hy Threshold
Mean After
Letter (sec.) .034 After Letter .030 After Letter .046
Range (sec.) .089 .074 .072
St Threshold
Mean After
Letter (sec.) .054 After Letter .037 After Letter .041
Range (sec.) .096 .080 .083
In this experiment, the observers A, H, and Hy, show an increasing
distance of the threshold mean after the visual stimulus, with the
successive introductions of the auditory series and the combined
series. In other words, the second column negative displacement is
larger than that of the first, and the third column has a still larger.
G and St are again exceptions, as they would be expected to be from
the above analysis of their methods. Each did his most accurate work
in a case where there was some rhythm present. St said in regard
to this work "the one pair abolishes the sound as a standard." The
rhythmic factor most missed by these observers, in the case of the
single pair, was the sound; for their results are almost the same in
the second and third columns. Introduction of the repetition of the
visual series does not make any decided difference. A, H, and Hy were
able so to adjust their attention as to get the best results in the
case of the single pair. The rhythm seemed to introduce for them a
subjective rhythm which upset the nice adjustment of attention and so
increased the displacement or the time between the threshold mean and
the visual stimulus. The negative displacement was increased under
these circumstances, probably as a result of the facilitation of the
auditory perceptive process. It has an _opened path_. It is a case of
pre-perception. Even when both were repeated (many pairs) the auditory
dominated, and so did the most at opening its path. But it seems more
likely to me that the rhythm, as such, whether auditory or auditory and
visual, claimed the attention and so proved a distraction from the work
of accurately discriminating the times of the impressions. And this
exaggerated the displacement or lack of discrimination in whichever
direction it was tending before.
In the successive stages of the investigation thus far, the
complication experiment has been stripped down by degrees to the
simple problem of the shortest possible interval between two disparate
stimuli,--in this case shortest auditory-visual and visual-auditory
intervals, as in the one-letter experiment of Table IV and the one-pair
experiment of Table VI. The various factors in the complication
experiment which have been successively analyzed out--the interval
between members of the auditory series, the length of the visual
series, the position of the visual series in relation to the auditory
stimulus, and the auditory series itself--have all been shown to be
factors intimately connected with the way the observer attends to
the stimuli in question. From the present standpoint, it may be said
they are all factors which, being introduced into the simple interval
discrimination experiment, modify the resulting judgment with regard to
the interval, by an interference with the normal attention-processes in
the discrimination of intervals.
INTERVAL DISCRIMINATION
The method of interval discrimination deserves special consideration.
Some of the introspective observations made by observers while engaged
in the work, already reported, are instructive in this connection. In
the case of a single pair, one observer said, "I know which is first
because it gets hit first." This remark is a very apt expression of
my own experience in trying to answer the same question. "Getting
hit first" clearly means, to my mind, some kind of _action_ on the
part of the observer. He was ready, in the moment of preparation for
the experiment, to see a flash of red with his right eye (either eye
could have been used) and to hear a click with his left ear. (The
stimuli were each produced 25 cm. from the respective sense-organs.)
His preparation consisted in securing the "hair-trigger" condition in
the two parts of the cortex and conduction apparatus immediately in
question in the sensing of the two expected stimuli, and other parts
are in a shut-off-from-discharge condition. This is the interpretation
which seems to me an appropriate explanation of the feeling of special
readiness to discharge in these two directions, when the expected
stimuli shall come. The eye- and ear-muscles, in such case, are held
tense on the sides (in the organs) where the stimuli are expected.
The breath is held, and the whole trunk is under a strain. All bodily
processes, in so far as they are controlled, are directed in such wise
as to get whichever of these expected impressions shall come first, in
as short time as possible, in order to know that it is first.
The reaction which gives the basis for the judgment may be a conscious
"hitting" of the first. Or it may be a reaction, ostensibly as a part
of the whole apperceptive process of which the auditory and visual
processes are parts. This reaction may be any one of many kinds.
Often it is a letting-go of the held breath. The exhalation or other
reaction comes in response to the whole stimulating or "setting-off"
process, and the one or the other of the two stimuli is judged to
be first by certain peculiar relations within the experience of the
moment. Such an explanation is in part suggested by the expression
of St, that the visual impression when it came before the auditory,
appeared as a "grace-note," and when it came after the auditory, as
an "after-strike." St played the piano. He himself thought that this
discrimination was a motor affair, _i. e._, a difference judged on
the basis of a difference in the motor response. The judgment of the
temporal order of the two impressions seemed to be an interpretation
or translation of the different motor responses.
A, whose method brought the shortest range in Tables IV, V, and VI,
said, "I hold my breath at the moment of expected stimulation, and it
goes at the first impression." At another time he said, "When I say
'click first' I have the feeling that the click is left, and when I say
'click last,' that the click is on the right." He interpreted this to
mean that when the click sounded first, he had moved slightly toward
it, that is, to the left, and that when the visual stimulus had come
first, he had moved slightly toward it (it was sensed by his left eye),
and this was rather away from the sound, which would have come before
the movement could have been more than initiated.
In my own case, I felt distinctly different motor responses in the
two cases. There was an immediate feeling of release in whichever
organ the stimulus first reached. A little involuntary jerk occurred
in the musculature of this sense-organ, and sometimes the head moved
slightly in the direction of the first stimulus. The condition of
the next moment from which the judgment proceeded seemed to be best
expressed thus, "I had it at a time when the other was not there." The
attention was accurately set for both. Right eye and left ear were both
distinctly innervated. The first stimulus "struck" the appropriate
organ, and the "set" of the organ was released.
I am persuaded that the difference in sensitivity to intervals between
auditory and visual impressions is due, in part, to a difference in
the power of "cocking the ear" to hear, as one fixates the eye to see.
The observers who got the smallest ranges between upper and lower
thresholds had the most distinct kinæsthetic sensations in the moment
of preparation, in the middle ear and about the external meatus.
All had some sensations from the side of the head in question. The
less accurate had a general feeling in the neck-muscles. Accuracy of
discrimination was in no wise connected with voluntary control of the
musculature moving the pinna. This was subject of careful enquiry with
all observers.
If this introspective evidence leads me aright, it seems that the
non-discriminable interval between auditory and visual impressions is
due principally to two things, (1) the impossibility of perfect balance
in the preparation of the attention for two expected stimuli, and (2)
the possible difference in time it takes to react to the different
impressions. The various complicating conditions which are added to
the simple interval discrimination in the cases of a complication
experiment, such as we started with in this investigation, are
chiefly interferences with the first-named factor. They disturb the
nice balances of attention. In this simple discrimination experiment,
under favorable conditions, a close approximation to a balance can
be attained. Any difference in the reaction-times to different
stimuli will remain as a constant error of displacement. It is well
known that reaction-times to visual stimuli are longer than those
to auditory. There is a retinal inertia which delays the perception
of the visual impression, in comparison with the auditory, coming
from exactly simultaneous stimuli. Having this physiological basis,
it will be relatively constant, as compared with the ever-varying
attention-differences.
THE COEXISTENCE OF MENTAL PROCESSES
Having given, then, these relatively fixed temperamental conditions of
reactions to different stimuli, which remain after practice (training
in the control of attention) has reduced the reactions to their
lowest terms, and has secured the conditions which are favorable for
the best balancing of the attention, there is yet one other question
very germane to the subject. It will have occurred already to any one
reading the above, that while the response to one stimulus is being
made, the other may be held in abeyance in the fringe region of the
attention-field, and that it is only brought up to clear perception
when the first has been disposed of. In other words, it may well be
that the first of two simultaneous but disparate stimuli, which gets
a start at setting-off its appropriate response in its sense-organ,
will bring out this response and be perceived before the other one
gets started,--that we do only one thing at a time,--that even in
such minute processes as this there is no possibility of division of
attention. It is hardly probable on the basis of the experimentation
already reported, that this is the case. There is some division of
attention. Otherwise there would be an equal certainty of judgment in
every case, no matter how small the separating interval. But still
the question as to how two mental processes, starting at the same
moment of time, do proceed, as compared to the progress of each of
the same processes when it holds the field alone, is very vital to
the understanding of the psychology of interval-discrimination. And
thus the question of objective time-relations is necessarily involved
in that of making judgments of the time-relations of simple mental
processes (subjective time-relations). The question is, Do these
processes, starting simultaneously, proceed just as freely as if they
were the sole occupants of the field of attention and so had the whole
energy of attention concentrated upon the single process, or do they
_interfere_ with each other?
Distribution of attention, of some sort, is granted. It is generally
conceded that there must be some sort of overlapping of the processes
in any complex mental operation. But there is the greatest lack
of information as to how this overlapping takes place,--as to the
mechanism of the distribution of attention. Fechner held to the notion
of a fixed maximum of available psychophysical energy. If this energy
is being consumed in a single process, that process is very vivid, and
all other processes are below the threshold. If, on the other hand, it
is distributed over several simultaneous processes, they are all of
diminished vividness. Distribution of attention always means diminution
of vividness, and concentration of attention, increase of vividness.
(See Elemente der Psychophysik, vol. 2, p. 451, 1860.) There is no
question of the truth of the last statement, and very likely Fechner's
fundamental concept is a true one; but there is need of more definite
data on the conditions and nature of simple mental processes occurring
at the same time, before it is considered proved.
Such researches as those of Paulhan,[115] Jastrow,[116] Loeb,[117]
and De Sanctis[118] all dealt with the combination of processes which
were themselves quite complex. It may well be that such processes as
reciting a poem, performing a subtraction or multiplication of long
numbers on paper, or keeping time with a metronome with the hand, seem
to go along together when combined, so that the time taken to do the
two of them together is much less than the sum of the times required
for their separate performance, and, in some cases, no greater than the
time required for either alone, and yet there may be no real proceeding
together. The apparent saving of time may be due, as Paulhan suggested,
to a rapid oscillation from one to the other of the two complex
processes which are largely automatic and can proceed, to such extent
as they are automatic, without any attention. This illustrates how
these investigations have probably missed the real point at issue with
regard to the division and distribution of attention. The attention
might be distributed over several of the minuter part-processes of
these processes so that many were proceeding at the same time, and yet
the method of these experiments would not reveal it. They were not
planned with sufficient precision. There is a problem in the division
of attention which they did not come within sight of, and this is the
real question of division in case of the simplest processes.
This problem is really that of the mechanism of mental assimilation.
The process it investigates is illustrated by the maturing collective
idea, as a melody or a spoken sentence. There is a gradual enrichment
or growth in meaning, as such a process goes on toward its completion.
At any instant during the process, implicit associative and nascent
perceptive elements are working together to their own mutual
clarification and explication. All focal content is the result of
complicated interworkings of such fringe material. It is impossible,
it seems to me, to question the causal relation of the fringe elements
or processes of one moment to the focal of the next; and it is equally
impossible to deny the complication of these same fringe processes.
They must go on at the same time in order to enter into one and the
same resultant process. The question of direct interest at this point
in the discussion is, To what extent do they proceed at the same time?
It would seem from the way in which this question, of the relationship
and interference of mental processes which proceed or start to proceed
at the same time, has come up in this investigation, that the natural
method of pursuing it would be that of comparing reaction times for
cognition reactions to the single and combined stimuli. But we are
warned against this by very clear inferences from an investigation of
Professor Münsterberg's in which he used the reaction method.[119]
By an ingenious use of the reaction experiment, the author shows
that two-part processes in a reaction, as, for example, a restricted
judgment of class and a subjective preference, occupy about the same
time when combined in a single reaction as when either is performed
in a separate reaction. In other words, two judgments of distinctly
different kinds can be made in the same time as either can be made when
it has all the attention concentrated upon it. The conclusion that
these elementary processes go on together--that at least there is some
degree of overlapping--seems unavoidable.
But when the first part of the same report is considered in relation
to the second, it is clearly shown that the reaction experiment is not
adapted to the finer investigation of this problem. For the first part
shows that no matter how much a _motor_ reaction is complicated by
choices or other judgments, it always takes place in just about the
same time as the simple reaction. The complications may be such as
actually to double the reaction time in the case of a sensory reaction,
and yet a motor reaction, under precisely the same conditions as far as
they may be the same for a motor, shows no increase in time. The "set"
of the attention in the motor reaction is, no doubt, such a change
in the order of succession of the parts of the process that some of
those, which come after the stimulus is received in the case of the
sensory reaction, are made to come before the stimulus in the motor.
When, however, it is found that the motor response to the question,
"Is this the name of a scientist, philosopher, poet, statesman, or
musician,--Sappho?" is made by the appropriate finger, as previously
agreed upon, in just as short a time as the observer can make a motor
response with any finger to a simple auditory stimulus, it indicates,
either that the whole of the choice judgment has been made before the
stimulus was received, or that the judgment itself is so automatic
that it is practically a reflex. This latter cannot be true. The
judgment, as conscious choice, cannot be made before the stimulus is
given, _i. e._, until the question is completed. And judgment cannot
be made automatic and yet be a judgment. In fact both alternatives are
untenable, and there is no other course than to hold the situation
which gave rise to them at fault. If the judgment process here required
previous to the reaction does take time apart from the processes of the
simple reaction, the reaction process is shown by these experiments to
be unable to exhibit it. A more microscopic method is demanded before
the matter can be settled.
The Leipsic method of measuring the scope of attention by means of
the tachistoscope is the standard means of securing data as to the
_number_ of elementary processes which can go on at the same time in
consciousness. The same question, with which we are here concerned,
grows directly out of the investigation of the number of processes
which can go on together. Wundt acknowledges the great difficulty which
inheres in the investigation of this problem.[120] Cattell's early work
with the tachistoscope showing the numbers of letters, syllables, and
words, which could be apperceived under the same objective conditions,
indicated the great importance of what we may best call _meaning_, in
apperception, and its influence on the number of different processes
which may proceed together. In fact the number depends upon the
definition of the unit with which the investigator starts out. Wirth,
the latest emendator of the tachistoscopic method, has shown,[121] in
a very thoroughgoing and genuinely constructive criticism of earlier
work, that the one question of primary importance in investigations
of the content of the moment of consciousness, _i. e._, scope of
attention, is to set forth the relative clearnesses of the elementary
processes there proceeding together. He shows that the different grades
of clearness which may present themselves in the field of consciousness
of a momentary act indicate, on the one hand, the impossibility of
sharply distinguishing the "scope of attention" from the "scope of
consciousness" as Wundt uses these terms, and, on the other, the
serious indefiniteness of any merely numerical statement of the scope
of attention. His main purpose is to set forth a method by which
this field can be enriched by exhaustive statements of the relative
clearnesses of the processes going on at the same time. All the work of
the present study had been performed before the publication of Wirth's
work. Otherwise some of his suggestions would have been used in the
plan of the experiments following. I may say, however, that I believe
the method here used has its own distinctive merits.
GENERAL METHOD FOR TESTS IN COEXISTENCE
Taking the suggestions offered by Professor Münsterberg's study of
apperceptive and associative processes, I selected simple _judgments
of comparison_ as the best means of trying-out this question of
coexistence. The perceptive act itself is made up of judgments, and
these may very properly be the processes studied in combination as in
the tachistoscopic experiment. But the judgment which has a previous
perceptive act as its condition, determining its start, seems to be
better under control. It is itself a central process, not dependent
upon the variations of the objective factors in sensation. My plan
was to have the stimuli so arranged as to give rise to two or more
perceived conditions at the same moment, and so have one or more
judgments of comparison between the perceived features made at the
moment the perceptions were completed and immediately stated. If one
makes two series of single judgments of comparison, and a series
wherein these two judgments are combined in a single act, all three
under precisely the same objective conditions, and the same subjective
conditions, saving only the necessary changes in the _direction_ of
the attention, and the percentage of correct judgments is recorded in
each case, providing always that in no single series of judgments were
the conditions such that all judgments could be correctly given, he
would then have reasonable grounds for making inferences with respect
to the _interference_ of simple mental processes going on at the same
time,--whether there is any, and, if there is, how much there is.
_Interference_ would be indicated by the _falling-off in percentage of
correct judgments as the combinations were increased_.
Such relative accuracy of judgments, single and combined, was the test
sought after and relied upon in the following experiments. It was very
necessary to have the objective conditions such that the results in
cases of single judgments, later to be combined, should be short of
absolute correctness, in order that interference from the combination
should show itself in impaired accuracy. Otherwise there might be some
_free energy of attention_, which could readily take up the extra work
when the judgments were combined, and so there would be no impairment
of accuracy. It was the aim to have the objective conditions, such as
duration and extent, so regulated that about ninety per cent correct
judgments resulted in the series of single judgments. If, then, when
two were combined, eighty per cent were given correctly, and when three
were combined, seventy per cent, the inference would seem reasonable
that this falling-off in correctness was due to interference. The
failure of the perceptive process, indicated by the ten per cent
incorrect judgments in the series of singles, would remain a _constant_
source of error throughout.
There is, however, one other source of increasing error, with the
increasing combination of judgments, supposed above. The judgment
processes might go on at the same time without any impairment of the
accuracy of the single judgment, and yet the results, as expressed,
might show a falling-off in accuracy. This imperfection would then be
due to a partial failure of the retentive and reproductive processes,
and not to the imperfection of the judgment processes. I have found
no sure means of separating this factor and excluding it. As the
experiments were arranged and conducted, though, I believe any
impairment in accuracy resulting from combination is more likely due to
interference of the judgment processes.
If neither of these factors is efficient, on the other hand, there will
result no falling-off in accuracy of results when single judgments are
combined. To be sure the conditions of the experiment, as outlined
so far, do not preclude the possibility of the combined judgments
occurring in succession, and so giving rise to as large a percentage
of correct results as when occurring singly. That is, while one of the
so-called combined judgments was in process, the latent conditions
of the other would remain for the moment as mere physiological or
possibly psychical dispositions, and to these one would "hark back" in
the next moment. Here the reaction method is suggested as the means of
assurance that this is not the case. But this method, we have already
seen, will not lend itself to work of such precision as this. The
probability of this succession of judgments is reduced to a minimum in
the experimental groups following.
It can be practically precluded by a prevention of all sensory images.
In these experiments every precaution was used to prevent them. In
all cases where visual stimuli were used, for instance, a brightly
illuminated blue field immediately succeeded the momentary stimulus,
while comparative darkness preceded it. I cannot be so sure that there
were no memory images functioning. But all observers were carefully
questioned on this point at frequent intervals during the experiments,
and no evidence of their existence was found in any case. I feel sure
sensory images were excluded and think memory images very improbable.
SINGLE AND COMBINED JUDGMENTS FROM VISUAL AND TACTUAL STIMULI
In this group of experiments, I used judgments from visual and tactual
stimuli, singly and in combination. Both stimuli were given by means
of a large pendulum in the Harvard laboratory, specially constructed
for Professor Münsterberg. This pendulum is about one and a half metres
in length. It is hung in a heavy steel frame which rests upon a large
table. A curved steel bar, concentric with the swing of the pendulum,
and ninety degrees in extent, is so set to the frame that it serves
as the attachment for an electro-magnet, at any point in the swing of
the pendulum. The pendulum-rod carries an armature which fits this
magnet. By means of this magnet, the pendulum may be held at any point
between the position of rest and forty-five degrees out in either
direction; and it may be released by _breaking_ the circuit through the
magnet. The pendulum also carries a segmental screen of about seventy
degrees extent. An opening about nine by eight centimetres near the
centre of the screen affords means of tachistoscopic observations. A
sliding shutter makes the slit as narrow as may be desired. In these
experiments a black tube was set up, at right angles to the direction
of the motion of the pendulum, and at the height of the slit in the
screen. On the other side of the pendulum screen, and directly opposite
the tube, was placed a support for holding the object to be shown.
The object for the visual stimulus was one of two light gray lines on a
black background. These lines were 4 mm. wide, and one 44 mm. long, and
the other 40 mm. The work was done in a dark room. The stimulus card
was illuminated by an electric light hanging between it and the screen.
Both cards were shown the observer several times, before experimenting,
till he was sure of their lengths. Upon one being shown, in experiment,
he was asked to say whether it was the longer or shorter. The touch
apparatus was so arranged that the experimenter could at will give
the observer one or two contacts on the back of his right hand. The
contacts were made by means of an electro-magnet. This was actuated by
a current which was _made_ by the closing of a switch which was secured
by a set-screw to the same curved steel bar as bore the pendulum
magnet. This switch was closed by the pendulum in passing. It was
adjustable on the bar. Another similar switch, opened by the falling
pendulum the next instant, removed the tactual stimuli. These switches
were so placed in the course of the pendulum fall that the tactual and
visual stimuli were exactly simultaneous. The tactual judgments were,
_one_ or _two_ points touched. Results are presented in Table VII for
three observers, A, B, and Bo. The number of series which were averaged
in each case is given, in order properly to weight the results.
TABLE VII
_Combined_
_Single_ _Single_ _Tactual_
_Obs._ _Tactual_ _Visual_ _and Visual_
A Number of series
averaged 3 3 3
Per cent Correct 80 89 79
Judgments \-------\/-------/
Average 84
B Number of series
averaged 5 5 5
Per cent Correct 72 78 78
Judgments \-------\/-------/
Average 75
Bo Number of series
averaged 5 5 5
Per cent Correct 88 71 78
Judgments \-------\/-------/
Average 79
In Table VIII are given A's results for further experimentation under
the same conditions, also for a pair of visual judgments, a pair of
tactual, and all four combined. One series of each of the five was
given each hour of experimentation. For the additional visual judgment,
the observer was required to say whether the line was _high_ or _low_.
It was of two heights from the lower edge of the card, 17 mm. and 20
mm. For the other tactual judgment, he reported the point or points
touched on the hand, as on the _right_ or _left_ side. The middle line
was traced by the experimenter, before tests, as often as the observer
wished to be reassured of its position.
TABLE VIII
_Tact._ _Two Tact._
_Obs._ _Sing._ _Sing._ _and_ _Two_ _Two_ _and_
_Tact_ _Vis._ _Vis._ _Tact._ _Vis._ _Two Vis._
A Number of series
averaged 6 6 6 6 6 6
Per cent Correct
Judgments 87 88 83 9 81 83
The next additional combination was a pair of judgments based upon
auditory stimuli. Four electric clickers were placed on the wall behind
the observer. Two were loud and two faint. Each pair was accurately
adjusted so they were of the same intensity and quality. One of each
pair, _i. e._, one loud and one faint, were hung about four feet to
the left of the observer's median plane. The other two were hung at
an equal distance to the right of this plane. The circuit making the
click was _made_ by a switch closed by the pendulum as it fell. The
experimenter by pressing any one of four buttons gave the one of
the clicks he desired. The observer's two judgments were as to the
_loudness_ and the _position of the click_.
TABLE IX
_Two Vis._ _Two Tact._ _Two Aud._
_Obs._ _Lgth._ _Pos._ _Num._ _Pos._ _Inten._ _Pos._
B Number of series
averaged 8 8 8 8 8 8
Per cent Correct 82 94 89 100 94 92
Judgments \----------------\ /----------------/
Average 91.7
Bo Number of series
averaged 12 12 12 12 12 12
Per cent Correct 77 91 87 97 81 82
Judgments \----------------\ /----------------/
Average 85.8
_Six Judgments Together_
_Visual_ _Tactual_ _Auditory_
_Obs._ _Lgth._ _Pos._ _Num._ _Pos._ _Inten._ _Pos._
B Number of series
averaged 14 14 14 14 14 14
Per cent Correct 89 97 86 96 70 86
Judgments \----------------\ /----------------/
Average 87.3
Bo Number of series
averaged 20 20 20 20 20 20
Per cent Correct 77 93 85 98 81 80
Judgments \----------------\ /----------------/
Average 85.7
It is evident, on the face of these returns, that there is no positive
assurance of interference. Each of these observers had been in some
part of the complication work. And so the inference from lack of
evidence here can be carried back to that work, and we may rest assured
that the lack of accuracy in interval discrimination work by these
observers was due in minimal measure, if in any, to interference of
the mental processes, auditory and visual, tending to proceed at the
same time. Some parts of the results here presented look like evidence
for interference. But there is, on the whole, just as much evidence
of what one might call facilitation, in combination, as there is of
interference.
There is one source of possible explanation for the non-appearance
of evidence of interference in these results: that is the fact that
the stimuli are disparate, and so probably take different times for
maturing. Thus the judgment processes, so far as they thus start
from disparate sensations, may start at different times. There was
good reason for using disparate stimuli first for the combination of
two mental processes, as this was the closest related to the simple
interval discrimination experiment to which the complication experiment
had been reduced. But this objection is now easily overridden by making
the conditions of experiment such that all judgments start from one and
the same perceptual process.
ONE, TWO, AND THREE JUDGMENTS BASED UPON A SINGLE SENSE-PERCEPTION
The conditions here were such that the perceptual basis for any one of
the single judgments was at the same time the possible basis for any
other single judgment and also for any or all of them combined. What
judgment or judgments were given depended entirely upon the directions
given, and the consequent preparation of the attention. Under these
conditions, there could no longer be any doubt about the even start
of all judgments, so far as outer conditions were concerned. The only
remaining cause of an uneven finish--lagging of a process, as shown by
its increased inaccuracy when combined--must be interference with its
progress by other processes going on at the same time.
Visual stimuli were used. The objects to give the perceptual basis
for the judgments were small rectangular openings in cardboard seen,
on exposure, by _transmitted_ light. These rectangular windows in the
cardboard were 2 cm. by 1 cm. and stood in the vertical position 1 cm.
apart. The judgments were all based upon differences existing between
these rectangles as shown. One of these differences was in _length_.
They might be of the same length, or either the right or left might
be 2 mm. longer than the other. Another difference was in _shade_.
This was secured by different thicknesses of paper, pasted over the
openings. Two shades were used. The opening on one side might be shown
as either the same brightness, brighter, or less bright. The third
difference was in the _number of lines_ which crossed the rectangles.
Two or three wires were placed across them horizontally and about 5 mm.
apart. Thus they had the same number of lines, or one had fewer or more
than the other.
The same large pendulum was used in these experiments. The moveable
magnet on the curved steel bar was kept in one position throughout.
It held the pendulum, ready for release, at twenty degrees from the
position of rest. The adjustable weight on the pendulum was also kept
in one position. The only adjustment which was changed during this
series of experiments was the width of the slit in the window of the
screen. This was varied from one millimetre to five. The whole time
during which any part of the two rectangles was in view (the total
exposure) with a 5 mm. slit was .033 sec.; with a 3 mm. slit .031 sec.;
with a 1 mm. slit .029 sec. These times were measured with a Hipp's
chronoscope. The entire visual field, embracing the two rectangles, was
about 2 cm. by 3 cm., and was about three fourths of a metre from the
observer's eye. It could be accurately fixated beforehand and fully
exploited during the moment of exposure.
The observer was always instructed to give his judgments in terms of
one of the two rectangles. If, for example, length was in question, he
should say of the left-hand rectangle that it was longer, shorter, or
of the same length as the right-hand one. The process of expressing
the judgments was also facilitated by using the terms plus, minus, and
equal, for all three sorts of judgments. This was a special aid to
expression where two or more judgments were in question at the same
time. In these cases the observer was always given an order beforehand,
in which the judgments were to be given. This order for the three
combined, for example, was always, "length, lines, shade," as in the
following tables. If, then, the judgments were given "plus, minus,
minus," it meant that the left-hand rectangle was longer, had fewer
lines, and was less bright than the right. The process of making these
interpretations, as well as the order, was made automatic with the
observer, by practice, before experimenting.
Three observers, A, B, and Y, were used in this experiment. The
judgments were made in series of ten. Each hour's work was distributed
over (1) several series of single judgments, (2) two at a time, and
(3) three at a time, the aim being to get an equal number of judgments
of each kind, length, lines, and shade, under each of the three
conditions. The results are given as general percentages of correct
results. To properly weight these averages, the number of series (of
ten judgments each) which are included in making up any average, is
given just above the average.
TABLE X
KEY: Lth = Length
Ln = Lines
Sh = Shade
_Single Judgment_ _Two Judgments_ _Three Judgments_
_Obs._ _Lth_ _Ln_ _Sh_ _Lth_ _Ln_ _Sh_ _Lth_ _Ln_ _Sh_
A Number of
series
averaged 11 12 10 15 17 14 11 11 11
Per cent
Correct
Judgments 95 93 96 90 91 83 94 91 89
\----\/----/ \----\/----/ \----\/----/
Average 95 88 91
B Number of
series
averaged 8 8 7 9 10 9 7 7 7
Per cent
Correct
Judgments 93 80 90 76 77 90 75 70 75
\----\/----/ \----\/----/ \----\/----/
Average 88 81 73
Y Number of
series
averaged 12 13 13 19 19 16 13 13 13
Per cent
Correct
Judgments 76 80 58 72 76 61 72 74 58
\----\/----/ \----\/----/ \----\/----/
Average 71 70 68
Since these general averages for the single judgments are so close
to those in pairs, it seemed possible that the presence of objective
differences, other than the single one asked for, might be a
distracting agent, and really interfere with the judgment process
in question. For example, when judgment on length was in question,
it might be possible to give it correctly a larger number of times,
if there were no differences in shade or lines, than if these were
present. Some careful test experiments were made with a view to
clearing up this situation. The observers in no case knew the nature
of the investigation, nor were they aware that other differences
were absent in some of the cases. The results presented in Table XI
certainly show that the presence of other differences than the one in
question is no cause of interference.
TABLE XI
_Length_ _Lines_ _Shade_
_With_ _With_ _With_
_Obs._ _Diffs._ _Alone_ _Diffs._ _Alone_ _Diffs._ _Alone_
A Number of
series
averaged 5 5 5 5 5 5
Per cent
Correct
Judgments 98 96 96 96 98 94
B Number of
series
averaged 5 5 5 5 5 5
Per cent
Correct
Judgments 90 92 96 94 78 84
Y Number of
series
averaged 7 8 8 8 7 8
Per cent
Correct
Judgments 73 76 75 64 88 67
Notwithstanding the precautions taken to secure the full energy of
attention for the single judgment process, as already indicated in the
discussion preliminary to these experiments,--namely, by making the
stimulation conditions so near the threshold that only a part of the
judgments could be given correctly,--there still appeared a probability
that there was free energy of attention during the single judgment
process. The observers seemed to do more work when more judgments were
asked for. If this is true, the results of Table X are not a true index
of interference. If there is free energy during the moment of making
the single judgment, this may readily be used for another process when
combined with the first, and so there will be no interference. This
is a sufficient proof so far as it has immediate bearing upon the
interval discrimination experiment, but the further question as to what
will take place if we can use this free energy, if it exists, in both
processes alike, is an important one for the question of the relation
of two processes going on together in consciousness.
To ascertain the fact in this matter, I performed a series of
experiments with the same observers, in which previous occupation
of the mind served as a distraction. The distraction consisted in a
simple arithmetical operation,--addition or subtraction. The moment
before giving the stimulus for the judgment processes,--in the place
of the "ready" signal, I would call out some numbers, as, for example,
"twenty-four from sixty-three" or "fifty-seven and fifteen," the
first indicating subtraction and the second addition. The answer to
the addition or subtraction was always given before the judgment or
judgments, to make sure that it was performed. And in any case where
the observer knew that the addition or subtraction was done before he
attended to the stimulus for the judgment, that particular test was
thrown out. The results are given in the same form as in Table X.
TABLE XII
(_Addition and Subtraction as a Distraction_)
KEY: Lth = Length
Ln = Lines
Sh = Shade
_Single Judgment_ _Two Judgments_ _Three Judgments_
_Obs._ _Lth_ _Ln_ _Sh_ _Lth_ _Ln_ _Sh_ _Lth_ _Ln_ _Sh_
A Number of
series
averaged 8 8 8 15 15 16 15 15 15
Per cent
Correct
Judgments 79 84 67 66 68 66 53 69 59
\----\/----/ \----\/----/ \----\/----/
Average 77 67 60
B Number of
series
averaged 6 4 5 8 7 11 7 7 7
Per cent
Correct
Judgments 57 70 60 66 44 53 51 50 44
\----\/----/ \----\/----/ \----\/----/
Average 62 54 52
Y Number of
series
averaged 8 8 7 15 16 15 14 14 14
Per cent
Correct
Judgments 66 60 51 56 62 56 66 57 55
\----\/----/ \----\/----/ \----\/----/
Average 59 58 59
These results (general average percentages) show, for observer A, a
more regular and somewhat larger falling-off with combination than in
Table X, for B and for Y, a diminished falling-off, and relatively less
for the three than for the two combined judgments. The percentages are
lower throughout. This is a result to be expected. But there is no
notable change in the relative lowering of two judgments in comparison
with single judgments, or of three in comparison with two, such as
should appear if, as supposed, in the experiment resulting in Table
X, there had been free energy of attention in the case of the single
judgment.
It was my aim in these experiments, with distraction through another
simultaneous process, to secure a uniform residue of attention for
the judgment processes, whether single, in twos, or in threes. The
arithmetical operations were therefore as uniform as possible. But
it may readily be that very unequal demands were made upon a given
observer by successive operations, one's automatisations in number-work
may be so various. These would no doubt tend to average up in the
course of the whole work running through several weeks. But in order
to make more sure of the point, I tried another means of using the
free energy of attention which may exist in the case of the single
judgment, namely, by suggesting a judgment or series of judgments just
before an exposure. It will be recalled that the order of judgments
was always the same as that of the tables, and that all were expressed
as minus, plus, or equal. So if the experimenter called out before
a three-judgment exposure, "plus, equal, minus," it would be in the
nature of a challenge to the observer to assure himself beyond a
doubt whether or not the exposure showed the left-hand rectangle as
longer than the right, having the same number of lines, and being less
bright. The so-called suggestion was a distinct factor in heightening
attention. This is shown especially in Y's case by the larger
percentage of correct judgments. Results are averaged in Table XIII.
TABLE XIII
(_Attention heightened by Suggested Judgments_)
KEY: Lth = Length
Ln = Lines
Sh = Shade
_Single Judgments_ _Two Judgments_ _Three Judgments_
_Obs._ _Lth_ _Ln_ _Sh_ _Lth_ _Ln_ _Sh_ _Lth_ _Ln_ _Sh_
A Number of
series
averaged 2 4 2 6 7 7 8 8 8
Per cent
Correct
Judgments 90 89 85 87 81 76 92 72 77
\----\/----/ \----\/----/ \----\/----/
Average 87 81 80
B Number of
series
averaged 4 3 4 8 9 7 8 8 8
Per cent
Correct
Judgments 85 70 92 84 80 83 84 74 81
\----\/----/ \----\/----/ \----\/----/
Average 82 82 80
Y Number of
series
averaged 6 6 5 11 13 12 16 16 16
Per cent
Correct
Judgments 88 75 94 90 81 77 89 74 70
\----\/----/ \----\/----/ \----\/----/
Average 86 83 78
An analysis of the results obtained from B to show the effect of the
suggestions is given in Table XIV.
TABLE XIV
_Single_ _Two_ _Three_
_Judgments_ _Judgments_ _Judgments_
Per cent of right suggs.
judged correctly 87 85 79
Per cent of wrong suggs.
judged correctly 73 77 80
The effect of the so-called suggestions in making for correct judgments
was then quite noticeable in the case of single judgments, less so in
two judgments, and none whatever in three. This observer was able to
overcome 73% to 80% of the wrong so-called suggestions. Now, when it
is considered that only 80% to 82% of all the judgments given by B
(see Table XIII) are correct, it is very clear that their action as
suggestions was very slight. They had an influence, however. It was
shown, as expected, in a heightened attention. This was especially the
case with Y. Compare his general averages in Table XIII with those in
Table X. This rise in general averages coincides with the impression of
the experimenter during the experiment. It seemed then that this was a
distinct challenge to keen attention on the part of Y. He is a man who
intends to make impartial observations for himself, and has no notion
of being told what he is to see. That his general averages of correct
judgments stand so much farther apart in this case with heightened
attention than in either of the others (see Tables X and XII) is
indicative of an interference of the judgment processes themselves.
Such a series of general averages as those of Y in Table XIII, as
those of B in Table X, or as those of A in Table XII, seem, in
themselves, and under the conditions of the experiment, to be pretty
clear indication of an interference of simple mental processes carried
on at the same time. The only other explanation is that suggested
above, namely, an interference of the processes of reproduction and
expression. The conditions of the experiment seem to reduce the
probability of this to a minimum. But the centre of interest, in
considering the results, does not lie in the question as to whether it
is interference of the judgment processes themselves or the processes
of their reproduction. The foreground is occupied by a prior question,
namely, whether there is any evidence here presented for interference.
For if there is interference of such processes, why does it not show
up in the results for each of the observers in each of the Tables X,
XII, and XIII? Of the nine cases here offered for comparison, only
the three above designated show what may be called clear evidence
of progressively increasing interference with increase of combined
processes proceeding at the same time.
Under these circumstances this cannot be accepted as indisputable
evidence of interference. Such results as those of A in Table X, where
correct judgments, two at the same time, are given in 88% of the cases,
and three at the same time, in 91% of the cases, stand directly opposed
to interference. They seem to show a facilitation by combination. This
is indeed possible where three and only three sorts of judgment are
worked with. It is the limiting case, and if more than one is asked
for it is really easier to give three than to select two. A himself
remarked that this was the case. A similar explanation holds concerning
the results of B in Table XII, and those of A in Table XIII. If such
an explanation is the true one, it is manifest that the "limit of
attention," of which mention has been made above, has probably not been
reached in any of these cases. On the whole, these experiments _seem
to indicate a small degree of interference of simple mental processes
going on at the same time_. But such interference _cannot be considered
proved_ by these experiments.
THE QUESTION OF SYNERGY
In connection with these last experiments, where the comparative
judgments all proceed from one definite perceptive act, and where
therefore the conditions are most accurately controlled for showing the
effect of interference, if it is a fact, there is yet another means
of looking into that question. This is afforded by the _similarity_
of the _means of expressing_ the different kinds of judgment. In
connection with the current emphasis given to the motor side of mental
processes, it is often urged that mental processes go on at the same
time when they are working together toward one and the same motor
out-go. Otherwise they are likely, at least, to hinder each other,
and to take their turns. If such is the case, the similarity of motor
out-go which is present in these cases, where all three judgments are
plus, or all minus, or all equal, ought to produce a larger percentage
of correct judgments than is found in cases where there are two or
three kinds of expression. Furthermore, if there is no interference
of the judgment processes as such, but, as supposed possible above,
the impaired accuracy of judgment in the combination of judgments is
due to the imperfection of the memory, this too will be diminished by
similarity of expression of the three judgments. In fact similarity
should reduce this source of error to a minimum. The results presented
in Tables X, XII, and XIII, for three combined judgments, were worked
over, so far as possible, and all cases where the three judgments, if
correctly made, would have been expressed similarly, were separated
out. The total number of such cases, and all those where the judgments
would have been properly expressed dissimilarly, are recorded for
each observer in Table XV. The number actually given correctly under
each class is also recorded, as well as the _percentage_ of correct
judgments in each class for each observer.
TABLE XV
KEY: TN = Total Number
CJ = Correct Judgments
N = Number
% = Per cent
_Judgments expressed_ _Judgments expressed_
_Similarly_ _Dissimilarly_
_Obs._ _TN_ _CJ_ _TN_ _CJ_
_N_ _%_ _N_ _%_
A 222 172 77 561 479 85
B 195 153 78 498 356 71
Y 372 277 74 863 572 66
If the results of B and Y were presented alone, they would seem to
indicate synergy of similarly expressed judgments. But those of A
are most strongly contradictory of such a working together of such
judgments. This is very surprising to me, as A had such a facility in
expressing these similar judgments, especially "equal, equal, equal,"
that it suggested this comparison. But the apparent facile expression
is here shown to have attended a diminished accuracy. No conclusion
can be drawn with respect to synergic influence from the similarity of
expression of judgments.
RELATION OF OBJECTIVE AND SUBJECTIVE SIMULTANEITY
Reviewing this work in combination of judgments with reference to its
bearing upon the complication results, and the interval discrimination
results, it seems that interference of simple mental processes going
on at the same time, though it appears to be a fact, showing itself in
impaired accuracy of processes combined, is yet quite inadequate to
explain the whole, or indeed, any considerable part of the synchronism,
as we may call the "click first" "click last" interval of Tables IV,
V, and VI. The slight amount of interference of such processes as
the auditory and visual perceptions, tending to proceed at the same
time, would tend to a very slight displacement of one with regard
to the other. It is true, for reasons already discussed, that this
time-difference is so slight and so difficult of seizure that it cannot
be measured, and so no measure is offered. We cannot, therefore, be
certain _how much_ of the non-detectable interval is due to this cause.
But the evidence offered in the above tables of results is ample
justification for the statement that _interference_ can be responsible
for only a _very small part_ of the "click first" "click last" interval.
In the case of this interval, as in that of an interval between any
disparate stimuli, a part of it must be due to the different resistance
or inertia of the sense-organs. The eye is undoubtedly slower than the
ear. This would at once suggest itself as the cause of the interval
between the threshold mean and the visual stimulus in the results
shown in Tables IV, V, and VI above. That is, vision being slower, an
auditory stimulus given at the same time as a visual will appear to be
earlier, and it may be given considerably later and yet appear earlier.
In general, therefore, so far as this cause is active, one would expect
that the interval, at which a sound must precede a visual stimulus
in order to be certainly distinguished as coming before the latter,
would be much shorter than the interval, at which a sound coming
after a visual stimulus could be unfailingly distinguished as coming
later. In other words, the centre of gravity of the "click first"
"click last" interval, so far as this visual inertia is the cause of
its displacement with reference to the visual stimulus time, will be
_after_ the visual stimulus.
In one case in my results, Table V, St, H middle, there is presented
an extreme where not only the centre of gravity (threshold mean) is
placed after the visual stimulus (letter), but the whole synchronous
period ("click first" "click last" interval) is after the visual
stimulus, so that a sound coming .008 sec. after the visual stimulus is
distinguished with certainty as coming before it. So also St, in Table
VI, one pair, the sound coming .006 sec. after is judged as coming
before the visual stimulus.
But the variety of displacements of the threshold mean in different
observers, and more particularly in the same observer under different
experimental conditions, indicates very clearly that there are factors
other than visual inertia which are quite as important, and perhaps
equally responsible for this displacement. In Table VI, H, one pair,
for example, the threshold mean is before the visual stimulus .011
sec. So in Table V, G, H first, and also H last, it is before the
letter .005 sec. In these cases there must be some factor or factors
quite as strong as this visual inertia, and counteractive to it. These
are, in part, the complex attention factors which have been referred
to already. Prominent among them are the rhythmic perception which
is so marked in St; the movement toward the first stimulus and the
"letting-go" of the breath, of A; the passive "striking" of the letter
by the sound, in the case of some of the observers; and the "cocking"
of the eye and the ear, of others. These all have to do with the length
and place of the "click first" "click last" interval quite as much as
does the visual inertia. But however this may be, of this inertia and
the other factors just now named, probably each has more to do with it
than does the interference of the perception processes themselves.
But after eliminating the parts played by each and all of these
agencies in the determination of the interval, there will remain a
period of "present time," in which there are no time-differences,
and no qualitative differences which lead the subject to suspect the
existence of time-differences. The mental content of this reduced
synchronous period in experience is _one experience_. The sound was
heard and the letter was seen, but they came _together_ as aspects of
_one_ experience. In the moment of perceiving either one, it was not
possible to say that the other was already a memory. In other words,
the _primary memory_ of either, whichever came first, had lasted over
into the perception of the second. There had been no perceivable
transformation of the first since the instant of its perception. At
the moment of the inception of the second process, the first was
still, to the perceiving subject, what it was at the moment of its own
inception. Though change was probably going on in the physiological
substrata of the mental process in question, in every minutest moment
of the interval, yet a certain amount of effect of this change had to
accumulate before the observer could become aware of the change, and so
be aware of the passing of time or of temporal difference. This was,
then, only a case of the working of the law of _relativity_. And the
perception of time is a function of the duration and amount of change
of mental process.
Looked at from this point of view, we see the whole explanation of the
existence, the amount, and the position of this synchronous period
under one rubric, if only we could grant the combination of mental
processes without interference. If mental processes go on together,
the sole ground of the imperceptibility of short periods of time
separating mental processes is in the fact that the first of these
processes _has not changed sufficiently to be known as different_, to
the perceiving subject. The minimal perceivable interval will vary
from man to man, and in the same man from time to time, inversely
as the amount of change per unit of time, in the process itself.
The same statement could be made in terms of vividness or relative
clearness. The more focal the idea or process, _i. e._, the more vivid
or relatively clear it is, the more rapid will be the changes and the
perception of those changes. Professor Münsterberg's physiological
explanation of vividness,[122] as due to the facilitation of the motor
discharge, has already found confirmation in the method of keenest
interval discrimination as outlined above. The more rapidly the first
process can get into action, the more is the discriminated interval
shortened. So in Exner's experiments, where it was known which of two
stimuli would come first, the interval was very much shorter than any
of my results, for the motor preparation could be made very complete
beforehand, as in a muscular reaction. Therefore the perceptible
change, upon perception of the stimulus, occurred in a shorter time.
Under any circumstances, the conditions, subjective or objective, which
make for rapid maturing (and by the principle of dynamogenesis maturing
means going over into action) of the mental process, make also for the
shortening of the least perceptible interval.
These conditions are as various as the gamut of human experience is
wide. There is nothing, from the primary temperamental characteristics
to the passing wave of feeling of the present moment, which does not
affect it. Most particularly, though, is it a matter of the relations
existing among the elementary processes striving to go on together.
Among the focal and fringe elements of a given moment of experience, no
matter how carefully the practised introspectionist may strive after
an ideal condition of monoideism, there is an incessant interaction.
There are all sorts of hindrances and facilitations. Herein is the
justification of Stern's statement that the "praesenzzeit," as he calls
it, "varies with the quantity and quality of conscious content, the
direction of attention, and the strength of psychical energy," and
that it cannot be assigned a maximal value but rather what he calls
an "optimal value." All that is included, in fact, in the complex
rubrics, _attention_ and _interest_, has to do with the length of this
indiscriminable interval.
Time-difference in consciousness is the very simplest thing in mental
life, for it is a case of the bare awareness of change. The elementary
time-judgment is mere judgment of change in content of consciousness.
In the experiment where one is asked to say which of two expected
stimuli comes first, however, the case is already complicated.
There must be a double preparation to react and to note the change
characteristic of each case, and so convert it into a time-judgment. In
the combination of two judgments, there is the same double expectancy,
preparation to react in two ways at once. In each experiment, the
preparation and shaping of expectation is the same as in reaction
experiments. In all reaction work, the short reaction comes as the
result of catching the attention wave at its most favorable point.
If the signal to react catches the idea of reaction in the mind of
the observer at the very focal point in consciousness, the shortest
reaction possible under the given conditions results. So in both the
combination experiment and the interval discrimination experiment, it
is very necessary to catch the attention wave, _equally prepared for
both or all the processes_, and at the highest crest of advancement.
Both demand the same preparation as a compound reaction. I believe it
is this inequality of balance of the attention between the various
processes that is responsible for the interference which is evidenced
in my results. This is my explanation of the appearance of impaired
accuracy for combinations for a given observer under some conditions
and the failure of any sign of impaired accuracy for the same
observer under other experimental conditions, or even under the same
experimental conditions at different times.
In the time-interval discrimination experiment the evenness of
balance in the attention wave will make for the shortest interval
discrimination, and the proportion between the two will be direct,
so far as other factors do not interfere. But there are special
interferences here. One of these is the fact that the two mental
processes do not set off at the same moment. No matter how even the
balance in attention at the moment of impact of the first of the two
stimuli, the preparation for the other, not yet set off, cannot be held
in equal readiness while this is going off. This discharge has already
disturbed the preparation to discharge in the other direction. In the
case of a given pair of stimuli of definite qualities and intensities,
the relation will be one of mutual facilitation for one interval of
separation and one of inhibition for another interval. In one case
the first opens the path for the second, being a case similar to the
summation of stimuli, and in the other, it draws all the available
energy in its own direction.
FOOTNOTES:
[Footnote 108: W. Wirth: Zur Theorie des Bewusstseinsumfanges und
seiner Messung, Philos. Studien, vol. 20, p. 487, 1902.]
[Footnote 109: Cattell: Ueber die Trägheit der Netzhaut und des
Sehcentrums, Philos. Studien, vol. 3, p. 94, 1886.]
[Footnote 110: Gonnessiat: L'Equation personnelle, Paris, 1892.]
[Footnote 111: Exner: Experimentelle Untersuchungen der einfachsten
psychischen Processe, Archiv. f. d. gesammte Physiologie, vol. 7, p.
601, 1873, and vol. 11, p. 581, 1875.]
[Footnote 112: Angell and Pierce: Researches upon Attention, American
Journal of Psychology, vol. 4, p. 528.]
[Footnote 113: Pflaum: Neue Untersuchungen u. d. Zeitverhältnisse der
Apperception einfacher Sinneseindrücke, Philos. Studien, vol. 15, p.
139.]
[Footnote 114: Peters: Aufmerksamkeit und Zeitverschiebung in der
Auffassung disparater Sinnesreize, Zeitschrift f. Psychologie, vol. 39,
p. 401, 1905.]
[Footnote 115: Paulhan: Revue Scientifique, vol. 39, p. 684.]
[Footnote 116: Jastrow: American Journal of Psychology, vol. 5, p. 239.]
[Footnote 117: Loeb: Archiv. f. gesammte Physiol., vol. 39, 1886.]
[Footnote 118: De Sanctis: Zeitschrift f. Psy. u. Physiol. d.
Sinnesorg., vol. 17, p. 205.]
[Footnote 119: Münsterberg: Willkürliche und unwillkürliche
Vorstellungsverbindung, Beiträge zur experimentellen Psychologie, vol.
1, pp. 64-188.]
[Footnote 120: Wundt: Physiol. Psy., 5th ed., vol. 3, p. 351.]
[Footnote 121: Wirth: Zur Theorie des Bewusstseinsumfanges und seiner
Messung, Philos. Studien, vol. 20, p. 487, 1902.]
[Footnote 122: Münsterberg: Grundzüge der Psychologie, vol. 1, p. 525.]
THE ESTIMATION OF NUMBER
BY C. T. BURNETT
I. There are situations not a few in life in which we find ourselves
estimating the number of objects in some group. Sometimes we desire
to know merely whether the group is large or small. Sometimes we try
to reach an absolute number that shall approximate roughly to the
real number. Sometimes, again, we only care to know whether the group
in question is more or less numerous than some other group that we
have before us or perhaps recall in memory. The public speaker finds
himself wondering whether this present scattering audience is larger
than the one that last night crowded into the front seats. The farmer
riding between adjoining orchards judges roughly the prospective yield
by a comparative estimate of the fruit in sight. The politician too
has an interest that is very notable indeed in such rough numerical
estimates. He asks himself, for example, whether the voters will be
more influenced by reports favorable to his party sent in from numerous
small towns or by such reports from a few large centres. Or perhaps he
is planning a demonstration in favor of his candidate. His problem then
is so to arrange his procession that five hundred men will look like
five thousand. Turning to another field, how is it that the enrolment
in some institutions of learning seems larger and the size of the
faculty more portentous than in other similar institutions that are
really of about the same size?
These examples bring to mind our interest in rough numerical estimates
and at the same time suggest the probability that we are swayed back
and forth in these estimations without ever a numerical difference
occurring in the objects of our judgment. These considerations lead us
on, then, to an enquiry about the factors that can thus influence our
estimation of number.
II. INFLUENCE OF FACTORS IN THE SAME SENSE-FIELD AS THE OBJECTS WHOSE
RELATIVE NUMEROUSNESS IS IN QUESTION.