Right-hand superiority for throwing but not for intercepting.

In humans, the organization of movements performed by both upper limbs, relies significantly on a left hemisphere "praxis" system that also subsumes speech function. Right hand preference may also be an expression of this left hemisphere dependence, arising from the preferential connections of the right hand to the left hemisphere. Consequently, a manual task that maximizes the spatial complexity of a target (presumably engaging right hemisphere mechanisms), while concurrently minimizing motor-programming demands, was expected to yield a diminished disparity in preference and performance between the hands. Left and right hand accuracy were measured independently for two motor tasks in 48 normal right-handed university students. In the first task, darts were thrown overhand at a stationary target. For the second task, subjects were asked to use the open hand to block (but not catch) projectiles launched at varying trajectories and velocities. ANOVA yielded a significant Hand x Task interaction, in which the left hand did not differ from the right hand in intercepting ability, but was significantly less accurate than the right hand for throwing. A sex difference favouring males was found for both tasks; this difference was not reducible to differences in physique or athleticism.