Unformatted text preview: th nonhuman infants. On the visual cliff
we have observed the behavior of chicks, turtles, rats, lambs, kids, pigs, kittens and dogs. These animals
showed various reactions, each of which proved to be characteristic of their species. In each case the
reaction is plainly related to the role of vision in the survival of the species, and the varied patterns of
behavior suggest something about the role of vision in evolution.
In the chick, for example, depth perception manifests itself with special rapidity. At an age of less than 24
hours the chick can be tested on the visual cliff. It never makes a "mistake" and always hops off the board on
the shallow side. Without doubt this finding is related to the fact that the chick, unlike many other young
birds, must scratch for itself a few hours after it is hatched.
Kids and lambs, like chicks, can be tested on the visual cliff as soon as they can stand. The response of these
animals is equally predictable. No goat or lamb ever stepped onto the glass of the deep side, even at one day
of age. When one of these animals was placed upon the glass on the deep side, it displayed characteristic
stereotyped behavior. It would refuse to put its feet down and would back up into a posture of defense, its
front legs rigid and its hind legs limp. In this state of immobility it could be pushed forward across the glass
until its head and field of vision crossed the edge of the surrounding solid surface, whereupon it would relax
and spring forward upon the surface.
At the Cornell Behavior Farm a group of experimenters has carried these experiments with kids and goats a
step further. They fixed the patterned material to a sheet of plywood and were thus able to adjust the
"depth" of the deep side. With the pattern held immediately beneath the glass, the animal would move
about the glass freely. With the optical floor dropped more than a foot below the glass, the animal would
immediately freeze into its defensive posture. Despite repeated experience of the tactual solidity of the
glass, the animals never lear...
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This document was uploaded on 01/30/2014.
- Winter '14
- Developmental Psychology