Earlier experiments rearing kittens with one eye closed and reversing the closure after a certain age, or rearing kittens in a rotating drum and reversing the direction after a certain age, suggest that the critical periods for ocular dominance and directional sensitivity may differ. Since these results were obtained by different investigators in different laboratories, we have made a direct comparison of the two types of visual deprivation. 2. Four pairs of litter-mate kittens (matched in weight) were reared. One animal in each pair was monocularly deprived with subsequent eye reversal; the other animal was directionally deprived with reversal of drum direction. All reversals took place at age 5 weeks. Both kittens in a given pair were either 'left first' (left eye open first or left direction first) or both were right first. One died prematurely. 3. Recordings were made from the visual cortex at some age after 4 months. Some recordings were made in the left cortex and some in the right. In all cases of monocular deprivation, the majority of cells were driven by the eye that was open last (i.e. open after 5 weeks of age). In all cases of directional deprivation, the majority of the cells preferred movement in the first direction of exposure (i.e. the direction before 5 weeks of age). 4. We conclude that the critical period for directional deprivation terminates earlier than the critical period for monocular deprivation.
