Period of susceptibility of kitten visual cortex to the effects of monocular deprivation extends beyond six months of age.

The duration of the sensitive period of the kitten visual cortex to the effects of monocular deprivation was explored by studies of the behavioral and physiological recovery from extended periods of monocular occlusion imposed from birth, and by examination of the physiological effects of a 3 month period of monocular occlusion imposed on animals at either 4, 5, 6, 7 or 8 months of age. Animals monocularly deprived until 4 months of age eventually show considerable behavioral and physiological recovery from the severe deficits observed immediately following termination of the period of deprivation. The conclusion that binocular connectivity may still be altered by the nature of the animal's visual input beyond 4 months of age was supported by the results obtained from animals that were monocularly deprived at 4 months of age or older. Animals deprived at either 4, 5 or 6 months showed a clear shift of cortical ocular dominance in favour of the non-deprived eye, but those deprived at 7 or 8 months showed approximately normal ocular dominance distributions. It is concluded that the sensitive period lasts at least twice as long as previously thought, to between 6 and 8 months of age.

Are curves detected by 'curvature detectors'?

Five experiments which attempted to evaluate the relationship between orientation and curvature selectivity in human vision are described. In the first two experiments, threshold elevation for curved gratings was measured after exposure to similar gratings, with the use of either an adaptation (experiment 1) or a masking (experiment 2) paradigm. In both experiments threshold elevation occurred which was selective for both the degree and the direction of curvature of the adapting pattern. Experiment 3 compared the effects of adapting to tilted rectilinear or vertical curved gratings upon threshold for a vertical rectilinear grating. Threshold elevation declined systematically as the adapting gratings were either tilted or made more curved. Experiment 4 measured curvature selectivity as a function of the orientation of a curved adapting grating. Threshold elevation declined as the adapting grating was tilted more, but curvature selectivity remained. Experiment 5 measured the orientation tuning for curved gratings directly. Threshold elevation declined to 50% of its maximum value at an adpating orientation of about 28 degrees. This was constant for all values of curvature used. The resulsts are discussed with reference to the question of whether the human visual system contains 'curvature detectors' or linear-contour detectors which respond to the tangents of curves.

Orientation anisotropy: incidence and magnitude in Caucasian and Chinese subjects.

Cutoff spatial frequencies for sine-wave gratings were measured at four orientations for 100 Caucasian and 24 Chinese subjects, all of whom were raised in carpentered enviornments. For the Caucasian subjects, average acuity for horizontal and vertical gratings was superior to that for obliques by about one-quarter of an octive. However, about 10 percent of subjects showed an anisotropy of about one-eight of an ovtave. The carpentered enviornment explanation of orientation anisotropy cannot, in its present form, account for the wide variety of response patterns obtained, nor the differences between Chinese and Caucasian subjects.