Relation of hand skill to spatial reasoning in male and female left-handers with left- and right-hand writing.

The relation of mental ability for spatial reasoning (Cattell's Culture Fair Intelligence Test) to hand skill assessed by peg-moving task was studied in normal left-handers. Nonlinear, quadratic relationships were established between these two parameters exhibiting different characteristics according to sex and writing hand. It was concluded that the contributions of the right and left cerebral hemispheres to the cognitive-motor output of the brain depend on sex and writing hand as well as the degree of left-handedness in left-handers.