Evidence for stimulus-response compatibility effects in a divided visual field study of cerebral lateralization.

The question addressed here was whether lateral asymmetry of processing might be influenced by response position, a factor which is usually considered irrelevant in divided visual field studies of cerebral lateralization. For this purpose a lexical decision task, which had previously been investigated with lateral unimanual two-finger choice reactions (Heister et al. 1983) was carried out under different manual and vocal response conditions so as to uncover possible S-R compatibility effects. In the first study, thirty-two subjects responded unimanually, with their responding hand held in a medial position. In the second study, twenty-four subjects responded vocally, i.e., in both cases the spatial (right/left) cues of the response position were eliminated. The reaction time advantage for compatible S-R pairings obtained with lateral hand position disappeared in the experiment with medial hand position, and the right-field superiority for vocal reactions was much smaller than the right-field superiority for right-hand reactions in the earlier lateral experiment. This indicates that an S-R compatibility effect contributed to the results of the earlier experiment. Thus, S-R compatibility can affect even unimanual reactions in lateralization studies.