Published papers

On the Wason selection task with the Sharing-rule, there are three major response patterns; 1) to select those cards that detect resource-provider's non-cooperation to in-group, 2) to select those cards that detect resource-provider's failure to exclude out-group parasitism, and 3) to select the cards that detect both types of rule violation. We examined the relationship between the individual differences on the Sharing-rule Wason selection task and the participants' general trust level. Results showed lower general trusters tended to select the cards that detect resource-provider's failure to exclude out-group parasitism. The higher general trusters showed a tendency to select only the cards that detect non-cooperation by resource-provider. These results suggest that individual differences on social rule reasoning are related to respondents' perception, cognition, and attitude towards the social world.

A multidisciplinary collaborative study examining cognition in a large sample of twins is outlined. A common experimental protocol and design is used in The Netherlands, Australia and Japan to measure cognitive ability using traditional IQ measures (i.e., psychometric IQ), processing speed (e.g., reaction time [RT] and inspection time [IT]), and working memory (e.g., spatial span, delayed response [DR] performance). The main aim is to investigate the genetic covariation among these cognitive phenotypes in order to use the correlated biological markers in future linkage and association analyses to detect quantitative-trait loci (QTLs). We outline the study and methodology, and report results from our preliminary analyses that examines the heritability of processing speed and working memory indices, and their phenotypic correlation with IQ. Heritability of Full Scale IQ was 87% in the Netherlands, 83% in Australia, and 71% in Japan. Heritability estimates for processing speed and working memory indices ranged from 33-64%. Associations of IQ with RT and IT (-0.28 to -0.36) replicated previous findings with those of higher cognitive ability showing faster speed of processing. Similarly, significant correlations were indicated between IQ and the spatial span working memory task (storage [0.31], executive processing [0.37]) and the DR working memory task (0.25), with those of higher cognitive ability showing better memory performance. These analyses establish the heritability of the processing speed and working memory measures to be used in our collaborative twin study of cognition, and support the findings that individual differences in processing speed and working memory may underlie individual differences in psychometric IQ.