The hypothesis was confirmed that postoperative disturbances of preoperatively learned light-discrimination habits are due to sensory impairments and not losses of memory. The experiments also suggested that the striate rat discriminates on the basis of luminous flux and indicate that Kliiver's analysis of the residual visual capacities of the striate monkey should be extended to the rat.

Two experiments investigated the development of visual cliff discrimination in infant hooded rats. Normal visual cliff responses were seen 2 days after eye opening, at about 16^17 days of age. These findings are in agreement with physiological experiments showing that visually evoked responses attain adult characteristics at about the same time. Normal visual cliff behavior was found to deteriorate after this age if animals could utilize tactual information. Repeated experience with the visual cliff, under conditions where tactual information can be used, has effects difficult to evaluate. Some animals tend to continue to avoid the shallow side of the cliff, while others do not. These differences seem to be related to the developmental age of the animals in a consistent manner.1 Requests for reprints may be sent to J.

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