No abstract

Factor analysis of 25 rating scales from Bayley's infant behavior record were performed for a sample of about 300-400 infant twins tested at 1 or more of the following ages: 3, 6, 9, 12, 18, and 24 months. The analysis provided 5 major factors and 2 minor factors that were considerably consistent at all ages. As defined by the scales with the strongest loadings, the major factors were denoted as task orientation, affect-extraversion, activity, auditory-visual awareness, and motor coordination, and the minor factors were denoted as kinds of mouthing behaviors. Further analyses by twin pairs generally provided higher concordance for identical pairs than for same-sex fraternal pairs, and the differences in concordance became more evident with an increase in age. Among the factors, task orientation showed the most persistent differences between identical and fraternal pairs. Profile analyses for all factors extracted at each age indicated that the profiles within identical pairs were more similar than profiles within fraternal pairs. Overall, the findings delineate some of the dimensions of temperament observed during testing and suggest that there are genetic influences on several behavioral characteristics and the organization of those characteristics during infancy.

Ratings of behaviors pertaining to inhibition were observed for 130 twins participating in a longitudinal study. Ratings were available for four ages (12, 18, 24, and 30 months) and from three sources at each age: direct observations obtained in a laboratory setting, direct observations obtained in conjunction with infant mental testing, and a temperament measure from a questionnaire completed by parents. For the individual twins, the age-to-age correlations were in the moderate range (.26 to .64). The situation-to-situation correlations were generally in the same range (.17 to .64). When the twins were recombined into twin pairs, within-pair (intraclass) correlations indicated that monozygotic (MZ) twins were more concordant than dizygotic (DZ) twins for each of the behaviors at each of the ages. Also, the MZ twins were more concordant for the direction and degree of behavioral change from age to age or from situation to situation. These data provide additional evidence for the biological influence on behavioral inhibition, a characteristic that has been studied in temperament and personality research. The results suggest that the trait of behavioral inhibition and a change in the trait are genetically conditioned. In addition, it is suggested that the concept of trait be expanded to include the person-centered biological regulation of change.

No abstract

Factor analysis of 25 rating scales from Bayley's infant behavior record were performed for a sample of about 300-400 infant twins tested at 1 or more of the following ages: 3, 6, 9, 12, 18, and 24 months. The analysis provided 5 major factors and 2 minor factors that were considerably consistent at all ages. As defined by the scales with the strongest loadings, the major factors were denoted as task orientation, affect-extraversion, activity, auditory-visual awareness, and motor coordination, and the minor factors were denoted as kinds of mouthing behaviors. Further analyses by twin pairs generally provided higher concordance for identical pairs than for same-sex fraternal pairs, and the differences in concordance became more evident with an increase in age. Among the factors, task orientation showed the most persistent differences between identical and fraternal pairs. Profile analyses for all factors extracted at each age indicated that the profiles within identical pairs were more similar than profiles within fraternal pairs. Overall, the findings delineate some of the dimensions of temperament observed during testing and suggest that there are genetic influences on several behavioral characteristics and the organization of those characteristics during infancy.