STIMULUS-TARGET COMPATIBILITY FOR REACHING MOVEMENTS

Reaction time, movement time, and initial direction of reaching moveme nts toward a target in left or right hemispace were measured. In Exper iment 1, the target of movement and hand had to be selected; movements toward the imperative stimulus were initiated faster than movements t oward the alternate target, and ipsilateral reaches were initiated fas ter than contralateral reaches. In Experiment 2, the difference betwee n ipsilateral and contralateral reaches disappeared when no selection of the hand had to occur. In Experiment 3, no target had to be selecte d, and only a stimulus-hand compatibility effect appeared. The results reveal different compatibility effects (stimulus-target, stimulus-han d, target-hand), implying that participants exploit different correspo ndences, depending on the degrees of freedom of the action. The notion of compatibility effects relating to movement targets offers a new pe rspective on the negative Simon effect and it questions the general co ncept of response codes.