The relationship between nonverbal intelligence, familial sinistrality and Geschwind scores in right-handed female subjects.

I proposed that there might be a strong relationship between the psychological and motor systems, and argued that hand preference could be related to intelligence; higher IQs are to be expected in right-handers with familial sinistrality (FS) than without FS (Tan, in press). This hypothesis was tested in this work. Cattle's Culture Fair Intelligence Test was used to assess the ability of spatial reasoning in right-handed females. Hand preference was assessed by the Edinburgh Handedness Questionnaire; a laterality score (Geschwind score) was calculated for each subject. The sample from the Nursery High-school had a significantly lower mean IQ than that from the Medical Faculty. The incidence for the consistent right-handers was significantly higher in the sample with lower mean IQ than that with higher mean IQ. The incidence for the weak right-handers was significantly higher in the sample with higher mean IQ than that with lower mean IQ. The incidence for familial sinistrality was significantly higher in the sample with higher mean IQ than that with lower mean IQ. It was concluded that handedness, familial sinistrality, and intelligence are interrelated traits; an attenuation in cerebral asymmetry as a result of an increase in the right hemisphere's mental abilities, reflecting itself in weak right-handedness in conjunction with FS, could be a prerequisite for well-developed nonverbal intelligence.