Effect of processing mode on the degree of motor asymmetry in the Manual Stroop Test

In a reaction-time study using conflicting Stroop colour-word stimuli and unimanual-choice responses, Schmit and Davis (1974) have provided data incidentally showing a right-hand advantage for the verbal processing of the material, contrasting with a left-hand advantage for the chromatic processing of the same material. The present experiment successfully replicated the interaction effect, using a within-subject design and a simplified procedure. This effect indicates the preferential involvement of the left hemisphere in the verbal processing of the Stroop material. More interestingly, it shows that it may be efficient to use the very simple laterality factors of the output sphere - such as the hand used to make the response - for the study of hemispheric lateralization of cognitive function.