Developmental psychology.pdf

Perception and Consciousness 161
One explanation suggested that it was due to kinesthetic sensations in the eyes
as they looked from one figure to the other. These muscle movements somehow produced
the phi phenomenon. But then a demonstration was set up in such a way that
eye movements could not possibly account for the outcome. Two pairs of figures were
used, one above the other, and the perceived movement was left to right in one instance
and right to left in the other. Since the eye movements could not occur in two opposite
directions at the same time, they could not be responsible for the illusion.
The phi phenomenon apparently is dependent on some fixed reaction of the
visual system to these particular stimulus relationships. It may ensure that we perceive
the motion in very fast-moving objects (Rock, 1975).
We all experience this illusion in motion pictures, which takes place as follows.
After an image appears, a shutter blocks all projected light, and a new frame with a
slightly different image moves into place. The shutter opens; this still image is projected
onto the screen; then it is blocked; and another slightly different image takes its
place. The whole sequence is repeated again and again, without any objective movement
on the screen, which would only be seen as a blur. Instead, the motion picture is
a dramatic example of the phi phenomenon.
Illusion of Distance Illusions involving distance and shape are even more common
than illusions of movement, and one group of investigators, believing that learning is
important, formulated the carpentered-world hypothesis. This hypothesis states that
people who live among rectangular doors, tables, walls, platforms, and benches develop
certain expectancies from this experience, making them especially susceptible to illusions
involving these patterns. The Zulus, in contrast, spend much time outdoors and recognize
the circle as the dominant pattern. When the Zulus were compared with some residents
of Illinois, the issue was the role of learning, and significant differences between the
two groups were found. The Americans were much more prone to illusions of distances
involving straight lines and rectangular geometric patterns (Herskovits, Campbell, &
Segall, 1969; Figure 6.14).
Altogether, 15 cultures were tested, and since susceptibility to this illusion was
found in all instances, biological factors are clearly involved to some degree. But the
large group differences indicate that experience is an augmenting factor. In fact, the
chief thrust of this chapter so far is that human perception, although dependent on
inherited sense organs and neural reactions, is something more than a simple reception
of information out there in the world around us. To this stimulation, we add the influence
of earlier learning.
Figure 6.14
Parallelogram Illusion. The AC
diagonal appears about the same
length as ВС, but it is 16 percent
shorter. If the parallelogram actually
were a table top seen from one side
and slightly above, the left-hand
diagonal would represent a greater
distance across the surface than the
right-hand diagonal. Hence it is
judged longer by people who live in a
"carpentered world" but not by the
Zulu of South Africa, who have
circular huts, circular cattle pens, and
other circular settings.