Operant eyelid conditioning in trisomy-18.

2 profoundly retarded children with extra No. 18 chromosomes were conditioned to emit operant eyeblinks in conformity with continuous and extinction schedules of reinforcement. Conditioning with each child was undertaken at normal feeding times, and when spoonfuls of food were made contingent upon blinking, blink rates increased. On interpolated and final sessions when food was given independently of blinking, blink rates fell to baseline level. This is the 1st reported evidence of learning in the trisomy-18 condition, probably because most of these children die before 1 yr. of age.