INTERFERENCE OF CONCOMITANT MOTOR AND VERBAL TASKS ON SIMPLE REACTION-TIME - HEMISPHERIC DIFFERENCE

Simple reaction time to a lateralized unstructured visual stimulus was studied in normal subjects while they were carrying out a concomitant task. The concomitant tasks were either verbal (subtracting serial 3's or 4's), praxic (complex pattern of finger movements) or consisting in a simple highly automatized pattern of finger movements. Verbal and praxic tasks produced an overall lengthening of simple reaction time with a specific marked slowing of responses to stimuli located in the right visual field. In the automatized task there was a mild general lengthening of reaction times but no visual field effect. The appearance of a strong left field superiority in simple reaction times when a verbal or praxic task is concomitantly carried out is interpreted in terms of interference between the activity of mechanisms mediating verbal and praxic behaviour and that of mechanisms responsible for the responses to stimuli presented in the right visual field. The possible loci of this interference are discussed. © 1979.