Kittens reared in a unidirectional environment: evidence for a critical period.

Abstract

Kittens were reared in the dark from birth except for a period each day when they were put inside a stationary transparent cylinder, around which a drum, with vertical black and white stripes on the inside, rotated in 1 direction. After the end of the period of exposure, a sample of single cells from their visual cortices were recorded and analyzed for direction and orientation sensitivity and other properties. Two kittens were placed inside the drum, rotating rightward, for 2 h each weekday for 3 1/2-7 wk of age. A greater proportion of the directionally sensitive cells in their cortices showed a preference for rightward movement. Six other kittens were placed inside the drum for 1 h each weekday from 2-12 wk of age with the drum rotating leftward up to a particular changeover age, then rightward until 12 wk. The changeover point occurred at 21, 26, 28, 33, 35 and 51 days for different kittens. A changeover earlier than 4 wk of age let to a preponderance of cells preferring rightward movement. A changeover later than 5 wk of age led to a preponderance of cells preferring leftward movement. The peak of the critical period for directional deprivation may occur earlier than the peak of the critical period for monocular deprivation. None of the samples of cells showed a preponderance of cells specific for vertical orientations. It is unclear whether this negative effect resulted from the presence of some horizontal contours during exposure, or some more fundamental cause.