Effects of irrelevant stimulus orientation on visually guided grasping movements

The present study investigated the effects of irrelevant stimulus orientation on visually guided grasping movements. Participants had to grasp a rectangular object at either the ends or the sides, depending on the color of a visual stimulus. In this task, correspondence between stimulus orientation and object orientation (stimulus-object congruency) and correspondence between stimulus orientation and hand orientation (stimulus-hand congruency) varied independently. Two experiments, with different sets of object orientations, revealed a consistent pattern of results. In particular, there were significant effects of stimulus-hand congruency, suggesting that perceiving an object activates congruently oriented hand movements. However, stimulus-object congruency had no effects, indicating that participants did not benefit from a preactivation of object orientation in the present task. The pattern of congruency effects implies that the cognitive representation, which is affected by irrelevant visual information, entails only those object or response features that are needed to select and control a response.