Right-handers and left-handers show differences and important similarities in task integration when performing manual and vocal tasks concurrently.

For a sample of 73 consistent left-handers, 46 inconsistent left-handers and 65 right-handers, reciprocal interactions between unimanual or bimanual tasks and concurrent reading tasks were shown to be a complex function of task characteristics and sample composition. The suggestion that subgrouping of left-handers [Hellige and Key, Cerebral Control of Speech and Limb Movements, North Holland, Amsterdam, 1990] influences task interactions in left-handers was borne out. Both manual and vocal performance were measured. The effects of the vocal task on the manual task were variable for groups and conditions, but an important common trend emerged: all handedness groups showed the same robust effect: vocal task performance was better when the right hand performed the manual task. Finally, speaking rate increased and tapping rate decreased during concurrent single hand tapping [cf. Hiscock, Brain Cognit. 1, 119-131, 1982]; and there was an opposite effect with concurrent bimanual tapping. The results favour a task integration model rather than an interference in cerebral functions space model.