Cross-age stability in emotional expressions during learning and extinction.

Three groups of infants who initially learned an arm-pull contingency at 2, 4, or 6 months of age were seen again in the same procedure 2 months later. Correlational analysis across a 2-month period for each group indicated that individual differences in emotional expressions were stable during learning and extinction. Specifically, anger during extinction and interest and enjoyment during learning were stable over a 2-month interval. Repeated experience did not affect learning performance or emotion