AbstractKittens reared with their mother under constant illumination from birth to 8 months were compared electrophysiologically, physically, and behaviorally with normally reared kittens. Initial components of visual electrocortical responses recorded from the light‐reared kittens in an awake state were of considerably greater magnitude in contrast to control kittens and adults. The light‐reared kittens also differed significantly in terms of minimal eye blink responses to light and to an approaching object and initially displayed continuous mydriasis independent of light‐dark conditions. The kittens did not differ in orientation to objects, following objects, visual placing, and visual cliff respo