Before I describe the results, 
I should explain that a long 
history of research in 
psychology and of observations 
in clinical neurology prompted 
this experiment. Psychologists 
had experimented extensively 
with visual deprivation in 
animals in the 1940s and 1950s, 
using behavioral methods to 
assess the effects. A typical 
experiment was to bring 
animals up from birth in 
complete darkness. When the 
animals were brought out into 
the light, they turned out to be 
blind or at least very defective 
visually. The blindness was to 
some extent reversible, but 
only slowly and not in most 
cases completely.

    Paralleling these 
experiments were clinical 
observations on children born 
with cataracts. A cataract is a 
condition in which the lens of 
the eye becomes milky, 
transmitting light but no longer 
permitting an image to form on 
the retina. Cataracts in 
newborns, like those in adults, 
are treated by removing the 
lenses surgically and 
compensating by fitting the 
child with an artificial lens 
implant or with thick glasses. 
In that way, a perfectly focused 
retinal image can be restored. 
Although the operation is 
relatively easy, 
ophthalmologists have been 
loath to do it in very young 
infants or babies, mainly 
because any operation at a very 
early age carries more risk 
statistically, although the risk 
is small. When cataracts were 
removed, say at an age of eight 
years, and glasses fitted, the 
results were bitterly 
disappointing. Eyesight was not 
restored at all: the child was 
blind as ever, and profound 
deficits persisted even after 
months or years of attempts to 
learn to see. A child would, for 
example, continue to be unable 
to tell a circle from a triangle. 
With hopes thus raised and 
dashed, the child was generally 
worse off, not better. We can 
contrast this with clinical 
experience in adults: a man of 
seventy-five develops cataracts 
and gradually loses sight in 
both eyes. After three years of 
blindness the cataracts are 
removed, glasses fitted, and 
vision is completely restored. 
The vision can even be better 
than it was before the cataracts 
developed, because all lenses 
yellow with age, and their 
removal results in a sky of 
marvelous blue seen otherwise 
only by children and young 
adults.

    It would seem that visual 
deprivation in children has 
adverse effects of a sort that do 
not occur at all in adults. 
Psychologists commonly and 
quite reasonably attributed the 
results of their experiments, as 
well as the clinical results, to a 
failure of the child to learn to 
see or, presumably the 
equivalent, to a failure of 
connections to develop for want 
of some kind of training 
experience.