Reversal of the behavioural effects of monocular deprivation in the kitten.

1. Eighteen kittens were monocularly deprived of vision until the age of 5, 6 or 7 weeks. Their eyes were then reverse‐sutured, and they were allowed to survive for 3‐63 days, before physiological recording from area 17. 2. At the time the reverse‐suture was performed, and immediately before the recording session, each kitten was tested separately in the two eyes to elicit five simple behavioural responses: optokinetic nystagmus, visual startle reaction, visually‐guided paw placing, visual following and negotiation of a "visual cliff". 3. Following the opening of their initially deprived eye, all kittens appeared behaviourally blind when forced to use that eye; their performance through the initially open eye was then perfect on all tests. After the period of reversed lid‐suture, however, their performance when using the initially deprived eye had improved, while that through the initially open eye deteriorated. This complementary improvement and deterioration was most rapid in kittens reverse‐sutured at the age of 5 weeks, and less rapid when reverse‐suturing was delayed until the age of 6 or 7 weeks. 4. Most of the kittens showed gross abnormalities of interocular alignment, and exhibited marked exotropia or esotropia. 5. The results of these tests were well correlated with the changes seen in cortical ocular dominance in the same animals.