With regard to the blind, much of what has been said above is
entirely irrelevant. However intimately we appreciate the function
of sight in our own mental development, it is almost impossible to
imagine how different our life would have been had we never seen.
But here, at the outset, a fundamental distinction must be drawn
between those blind from birth or early infancy, and those who lose
their sight in youth or adult life.[13] "It is better to have seen
and lost one's sight than never to have seen at all," is quite
as true as the sentiment which this form of statement parodies.
Expressed physiologically, this means, that to have begun the general
brain-building process with the aid of the eye insures some further
self-development of the visual centre, and thus makes possible a
kind of mental possession of which those born blind are inevitably
deprived.[14]
A fact of prime importance regarding the development of the
sight-centre is the age at which its education is sufficiently
completed to enable it to continue its function without further
object-lessons on the part of the retina. If we accept as the test
of the independent existence of the sight-centre its automatic
excitation in dreams, the question can be answered by determining the
age of the onset of blindness, which divides those who do not from
those who still retain in their dream-life the images derived from
the world of sight. The data that enable me to answer this question
were gathered at the Institutions for the Blind in Philadelphia and
Baltimore. Nearly 200 persons of both sexes were personally examined,
and their answers to quite a long series of questions recorded. All
dates and ages were verified by the register of the institution, and
the degree of sight was tested.
Beginning with cases of _total_ blindness (including under this head
those upon whom light has simply a general subjective "heat-effect,"
enabling them to distinguish between night and day, between shade and
sunshine, but inducing little or no tendency to project the cause of
the sensation into the external world), I find on my list fifty-eight
such cases. Of these, thirty-two became blind before the completion
of their fifth year, and _not one_ of this group of thirty-two sees
in dreams. Six became blind between the fifth and the seventh year:
of these, four have dreams of seeing, but two of them do so seldom
and with some vagueness; while two never dream of seeing at all. Of
twenty persons who became blind after their seventh year _all_ have
"dream-vision"--as I shall term the faculty of seeing in dreams. _The
period from the fifth to the seventh year is thus indicated as the
critical one._ Before this age the visual centre is undergoing its
elementary education; its life is closely dependent upon the constant
food-supply of sensations; and when these are cut off by blindness,
it degenerates and decays. If blindness occurs between the fifth and
the seventh years, the preservation of the visualizing power depends
on the degree of development of the individual. If the faculty is
retained, it is neither stable nor pronounced. If sight is lost
after the seventh year, the sight-centre can, in spite of the loss,
maintain its function; and the dreams of such an individual may be
hardly distinguishable from those of a seeing person.
It was a very unexpected discovery, to find, after I had planned and
partly completed this investigation, that I had a predecessor. So
long ago as 1838, Dr. G. Heermann studied the dreams of the blind
with the view of determining this same question, the physiological
significance of which, however, was not then clearly understood.
He records the answers of fourteen totally blind persons who lost
their sight previous to their fifth year, and _none_ of these has
dream-vision. Of four who lost their sight between the fifth and
the seventh year, one has dream-vision; one has it dimly and
occasionally; and two do not definitely know. Of thirty-five who
became blind after their seventh year _all_ have dream-vision. The
two independent researches thus yield the very same conclusion. Dr.
Heermann includes in his list many aged persons, and from their
answers is able to conclude that, generally speaking, those who
become blind in mature life retain the power of dream-vision longer
than those who become blind nearer the critical age of five to seven
years. He records twelve cases where dream-vision still continues
after a blindness of from ten to fifteen years, four of from fifteen
to twenty years, four of from twenty to twenty-five years, and one
of thirty-five years. In one case dream-vision was maintained for
fifty-two, and in another for fifty-four years, but then faded
out.[15]
With regard to the _partially_ blind, the question most analogous to
the persistence of dream-vision after total blindness, is whether
or not the dream-vision is brighter and clearer than that of waking
life; whether the sight-centre maintains the full normal power
to which it was educated, or whether the partial loss of sight
has essentially altered and replaced it. To this rather difficult
question I have fewer and less satisfactory answers than to the
former inquiry; but the evidence is perfectly in accord with the
previous conclusions. Of twenty-three who describe their dream-vision
as _only as clear_ as waking sight, _all_ became blind _not
later_ than the close of their _fifth year_; while of twenty-four
whose dream-vision is more or less markedly _clearer_ than their
partial sight, _all_ lost their full sight _not earlier_ than
their _sixth year_.[16] The age that marks off those to whom total
blindness carries with it the loss of dream-vision from those whose
dream-vision continues, is thus the age at which the sight-centre has
reached a sufficient stage of development to enable it to maintain
its full function, when partially or totally deprived of retinal
stimulation. The same age is also assigned by some authorities as the
limiting age at which deafness will cause muteness (unless special
pains be taken to prevent it); while later the vocal organs, though
trained to action by the ear, can perform their duties without
the teacher's aid. This, too, is assigned as the earliest age at
which we have a remembrance of ourselves. This last statement I am
able to test by one hundred answers, collected among these blind
persons, to the question, "What is your earliest remembrance of
yourself?" The average age to which these memories go back is 5.2
years; seventy-nine instances being included between the third and
the sixth years. At this period of child development--the centre of
which is at about the close of the fifth year--there seems to be a
general declaration of independence of the sense-centres from their
food-supply of sensations. Mr. Sully finds sense, imagination, and
abstraction to be the order in which the precocity of great men
reveals itself; and the critical period which we are now considering
seems to mark the point at which imagination and abstraction as
permanent mental powers ordinarily come into play. M. Perez likewise
recognizes the distinctive character of this era of childhood by
making the second part of his "Child Psychology" embrace the period
from the third to the seventh year.