Early experience effects on the development of fear in the squirrel monkey

This study was conducted to determine whether juvenile squirrel monkeys exposed to a snake for a 60-min episode during the preweaning period display behavioral and physiological responses to a snake similar to those displayed by feral-born adult monkeys. Juvenile male monkeys born to feral mothers in the lab were either exposed to a live snake during infancy or were snake-naive. Simultaneously tested were adult feral-born and adult lab-born (snake-naive) males. Juveniles exposed as infants to a snake displayed behavioral responses and plasma cortisol elevations following exposure to the snake that were similar to those of feral-born adults. In contrast, the snake-naive monkeys, regardless of age, rarely vocalized at the snake and displayed lower plasma cortisol elevations. These behavioral and physiological responses did not appear to be elicited by a moving animate stimulus per se, insofar as exposure to a moving fish elicited minimal behavioral changes and no cortisol elevations. In contrast to previous findings, these studies indicate that lab-born snake-naive squirrel monkeys are responsive to snakes, but that experience with snakes in infancy produces behavioral and physiological responses more similar to those observed in feral-born monkeys.