Reversal of the behavioural effects of monocular deprivation as a function of age in the kitten.

In order to evaluate the role played by chronological age or maturation in the decline of cortical plasticity during the critical period, kittens were given equal periods of monocular visual experience with each eye, separated by periods of dark-rearing. Experience with one eye was given at the same age in all animals (days 26-36), whereas the age at onset of reversal experience varied across animals. Monocular visual acuities were used as a behavioural index of sensitivity to reverse suturing. Our results demonstrate that sensitivity to reversal varies as a function of age alone when amount of visual experience is held constant. The size and direction of the interocular differences in visual acuity indicate that sensitivity declines steadily throughout the critical period. If reversal occurred on or before day 57, the initially deprived eye was able to gain superiority over the initially exposed eye. By 14 weeks of age the effects of reversal were negligible. The duration of dark-rearing within and beyond the critical period appeared to affect the absolute acuity levels attained but not the magnitude of interocular acuity differences.