This study was concerned with determining the effects of visual and proprioceptive experiences, during the early life of rats, on their emotional, perceptual, and problem-solving behavior at adulthood. The problem arose out of the work of Hebb and his associates (3,4,5,6). Hebb has suggested that the organization of adult behavior is largely determined by the quality of infant experience and learning (4). This early learning is so important because it produces permanent changes in the structure of the central nervous system, primarily the cerebral cortex (5).The brief history of research in this area was summarized by Hymovitch (6), who found that rats reared in a complex free environment were significantly superior in problem-solving ability, as measured by the Hebb-Williams test, to those reared in a restricted environment. The complex free environment was a large box containing a number of "playthings" (small metal and wooden structures), which enabled the rats to have a variety of experience. He also placed in this box a number of small mesh cages in which smaller groups of rats were reared. The mesh cages were periodically moved from place to place both inside and outside the box. The problemsolving behavior of these rats, as adults, was as good as that of the animals reared in the entire box. In a similar study Forgays and Forgays (3) reported, among other facts, that the rats reared in mesh cages were inferior, in problem-solving behavior, to animals reared in a large, complex free environment. Although these two sets of results are somewhat inconsistent, both authors concluded that early perceptual experience or learning seemed to play a dominant role in determining 1 This paper is based on a dissertation, supervised by Professor R. B. MacLeod, which was submitted to Cornell University in partial fulfillment of the requirements for the degree of Doctor of Philosophy and is on file in the library of Cornel] University. The research was partly financed by scholarships from the Canadian National Research Council.

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To test the hypothesis that rats that have perceptual experience with specific visual forms early in infancy will be superior in form discrimination to rats having comparable experiences later, one group was continuously exposed to triangles and crosses from the age of 16 to 41 days and another group lived with the same figures from 41 to 66 days. Two control groups with minimum visual form experience were used. Each form-experienced group was superior to the control group of the same age, and the early experienced group was superior to the late group in both form discrimination and generalization. The results are consistent with Hebb's position that learning is more effective when it occurs earlier in life.