Infants' responses to arm restraint at 2 and 6 months: a longitudinal study.

This study examined the continuity, stability, and change of infants' responses to a frustrating event (i.e., arm restraint) between 2 and 6 months in terms of both negative reactivity and its regulation. Fifty-two healthy, full-term infants and their mothers participated in an arm restraint procedure. Infant behaviors were observed and coded at 3-s intervals. The results showed that infants' reactivity to frustration and their ability to regulate such reactivity significantly changed in level over time. Individual differences in frustration reactivity were stable across the two ages; two regulatory behaviors (i.e., orientation to mother and avoidance) could be observed in the same percentage of babies at both 2 and 6 months. At 6 months, several significant associations between frustration reactivity and infant regulatory behaviors emerged. These findings suggest that the arm restraint procedure may be usefully employed to study individual differences in infants as young as 2 months of age.