Developmental psychology.pdf

158 Modes of Awareness
'When I was younger I would
stare for hours at distant things,
pointing my finger directly at things
with both eyes open, and then
close first one eye, then the other.
The object I focused on seemed to
move its position, and I used to
think that there was something
wrong with my eyes.
increases for objects close at hand and decreases when more distant objects are brought
into focus. This adjustment by muscles attached to the eye mechanisms provides the
brain with information about the relative distance of perceived objects.
There are in addition two generally recognized binocular cues, requiring both
eyes, and both are physiological. In convergence, the eyes turn inward as we look at
objects. They do so more for nearby objects than for distant ones, and therefore convergence
is an effective distance cue only for objects within a few meters of the viewer.
These movements prevent blurred vision by placing the image closest to the fovea,
where vision is clearest.
Finally, since the eyes have different locations in the head, each also obtains
a somewhat different view of the same object, as can be experienced by holding a small
object near your face and alternately closing one eye and then the other. The right eye
sees more of the one side whereas the left eye sees more of the other.* This difference,
referred to as retinal disparity, is greater for closer than for distant objects. It too is a
useful distance cue, especially for nearby objects.
Development of Visual Space Cues The behavior of animals and young children
suggests that some of these cues are innate. Animals born with their eyes open and
able to move around soon after birth avoid a cliff without prior experience. Human
beings cannot be tested until they are able to crawl, at the age of six months or so, at
which time they too avoid a cliff, but considerable learning has already occurred (Figure
6.13). Victor, as we saw, had a definite aversion to such situations.
It has been demonstrated that active movement in the environment aids in the
development of space perception. After two groups of kittens were raised in darkness,
one group was given a ride every day in a small carousel, from which their environment
could only be seen. The other group had the same visual experience, but it was achieved
by walking around instead. Afterward, when the kittens were presented with some
problem in space perception, the results were quite clear. The passive kittens, after
riding in the carousel, showed no awareness of a precipice, but none of the walkers
went over the cliff. The visual cues came to have meaning for them through association
with the muscular and tactual experiences (Held & Hein, 1963; Hein, Held, & Gower,
1970).
Figure 6,13
Testing Space Perception. This
apparatus is called a "visual cliff"
because it only presents the
appearance of a cliff. On one side of
the center board the patterned
squares are directly under the glass,
and on the other side they are on the
floor. When human infants are
induced to leave the firm middle
board, almost all of them crawl onto
the "shallow" cliff (Gibson & Walk,
1960).