Falligant, E.L., & DiLalla, L.F. (1993). Application of an augmented index of behavioral inhibition in toddler twins. Poster presented to the Life Span Development Conference, March, 1993, Carbondale, IL.

Inhibition is the consistent tendency to become quiet, cease activity, and withdraw when confronted with unfamiliar places, people, or objects. DiLalla and Kagan and colleagues have reported an inhibition aggregate based on peer play behaviors which is stable and has been demonstrated to have a strong genetic component. The present study explored an additional component to inhibition: extended "warm up periods" or latencies to engage in certain behaviors. 158, 24-month-old twin pairs and 108, 36-month-old twin pairs were assessed via peer play interactions. An intraclass correlation comparison between monozygotic and dizygotic twins showed that the heritability for inhibited behavior, now represented by the revised aggregate, was fairly strong, approximately .5. The correlations at 24 months were r_mz=.77 and r_dz=.50, and at 36 months were r_mz=.27 and r_dz= -.06. This suggests that inhibition, when including long latencies to certain activities, has a stronger genetic component at 24 months than at 36 months. Furthermore, the inhibition indices across the two time periods were significantly correlated, suggesting that inhibition as represented by these long latency periods is a moderately stable construct.