ABSTRACTS OF ISSID KEYNOTE LECTURES


MON, July 17, 8:30 - 9:30 a.m.

INTELLIGENCE AND THE DIFFERENTIATION HYPOTHESIS

General intelligence (Spearman's g) accounts for over 50% of the reliable variance in a battery of mental tests in a sample of the general population. In a 'differentiation hypothesis' originally suggested by Spearman, it is hypothesized that the degree to which g pervades performance on mental tests is greater at lower ability levels. Others have suggested that g is more pervasive at lower ages. This presentation addresses four topics with respect to the differentiation hypothesis. First, a novel historical review of studies addressing the differentiation hypothesis is presented. Second, recent studies are critically discussed and the differentiation hypothesis, drawing from a pool of over 10,000 subjects, is presented. This reveals that, when groups were selected on the basis of verbal, numerical or spatial ability, the below-average ability groups had a more pervasive g factor, confirming the differentiation hypothesis. Fourth, the implications of the differentiation hypothesis and possible mechanisms of differentiation are discussed.




TUES, July 18, 8:30 - 9:30 a.m.

MOLECULAR GENETICS AND THE STUDY OF INDIVIDUAL DIFFERENCES

Twin and adoption studies have built a strong case for the importance of genetic factors for many behavioural dimensions and disorders, including complex personality traits. The time has come to harness the power of molecular genetics to begin to identify specific genes involved in personality dimensions and disorders. The challenge is to use molecular genetic techniques to identify genes involved in such complex systems influenced by multiple genes as well as multiple nongenetic factors, especially when any individual gene is neither necessary nor sufficient. Animal models of temperament are especially powerful in identifying chromosomal regions and genes for complex traits in the human species. The basics of new molecular genetics are described and initial results for personality are presented.




WED, July 19, 8:30 - 9:30 a.m.

THE NURTURE OF INDIVIDUAL DIFFERENCES

Within the past century the study of environmental (nurture) contributions to individual differences has occurred in three phases. Phase I research was centered around the question of whether the environment could influence variability in individual differences. For the most part this question has been answered in the affirmative. Phase II research was centered around the question of what aspects of the environment were most salient for variability in individual differences. As a result of this research, we have been able to identify a number of specific environmental dimensions that are reliably related to various developmental outcomes. Current Phase III environmental research and theory is centered around two questions: (a) What is the structure of the environment; (b) How does the environment operate to influence variability in individual development. Each of these questions will be discussed in turn, with specific emphasis on the role of higher-order environmental moderation, bidirectional organism-environment transactions, environmental specificity, organism-environment covariance and organism-environment interaction in promoting variability in individual differences. Implications of these environmental action principles for integrative nature-nurture studies and for interventions will also be discussed.