The first experiments along this line were performed

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Unformatted text preview: ortant clues to the relative roles of maturation and learning in animal behavior. The first experiments along this line were performed by K. S. Lashley and James T. Russell at the University of Chicago in 1934. They tested light-reared and dark-reared rats on a "jumping stand" from which they induced animals to leap toward a platform placed at varying distances. Upon finding that both groups of animals jumped with a force closely correlated with distance, they concluded that depth perception in rats is innate. Other investigators have pointed out, however, that the dark-reared rats required a certain amount of "pretraining" in the light before they could be made to jump. Since the visual- cliff technique requires no pretraining, we employed it to test groups of light-reared and dark-reared hooded rats. At the age of 90 days both groups showed the same preference for the shallow side of the apparatus, confirming Lashley’s and Russell’s conclusion. Recalling our findings in the young rat, we then took up the question of whether the dark- reared rats relied upon motion parallax or upon contrast in texture density to discriminate depth. When the animals were confronted with the visual cliff, cued only by motion parallax, they preferred the shallow side, as had the light-reared animals. When the choice was cued by pattern density, however, they departed from the pattern of the normal animals and showed no significant preference (Fig. 5). The behavior of dark - reared rats thus resembles that of the day-old chicks, which also lack visual experience. It seems likely, therefore, that of the two cues only motion parallax is an innate cue for depth discrimination. Responses to differential pattern-density may be learned later. One cannot automatically extrapolate these results to other species. But experiments with dark-reared kittens indicate that in these animals, too, depth perception matures independently of trial and error learning. In the kitten, however, light is necessary for normal visual maturation. Kittens reared in the dark to the...
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This document was uploaded on 01/30/2014.

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