Handling rabbits in infancy: in search of a critical period.

In Experiment 1 rabbits were handled for the first 10 days of life while controls were not disturbed. In Experiment 2 rabbits were handled on Days 11–20. In Experiment 3 rabbits were handled on Days 1–10, 11–20, 1–20, or were not handled. Starting at 31 days the animals were given an open-field test, a test for exploratory behavior toward novel stimuli, and a test of social behavior. The data were not consistent with the critical period concept. Instead, handling during the first and second 10-day intervals appears to be additive and to approximate the effects of 20 days of handling.