Nonverbal intelligence, familial sinistrality and left-handedness

The interrelations among Geschwind scores, familial sinistrality, and nonverbal intelligence were studies in left-handed males and females. Nonverbal intelligence (spatial reasoning) was assessed by Cattle's Culture Fair Intelligence Test. Hand preference was assessed by the Edinburgh Handedness Inventory, and a laterality score (Geschwind score) was calculated for each subject. The mental ability for spatial reasoning was found to be related to the degree of the left-hand preference in conjunction with familial sinistrality. Moderate left-handedness was found to be advantageous for nonverbal intelligence. It was concluded that cognitive and motor functions are interrelated systems; the efficiency of the spatial reasoning would depend on the degree and developmental level of cerebral lateralization.