Grasp Posture Alters Visual Processing Biases Near the Hands

Observers experience biases in visual processing for objects within easy reach of their hands; these biases may assist them in evaluating items that are candidates for action. I investigated the hypothesis that hand postures that afford different types of actions differentially bias vision. Across three experiments, participants performed global-motion-detection and global-form-perception tasks while their hands were positioned (a) near the display in a posture affording a power grasp, (b) near the display in a posture affording a precision grasp, or (c) in their laps. Although the power-grasp posture facilitated performance on the motion-detection task, the precision-grasp posture instead facilitated performance on the form-perception task. These results suggest that the visual system weights processing on the basis of an observer's current affordances for specific actions: Fast and forceful power grasps enhance temporal sensitivity, whereas detail-oriented precision grasps enhance spatial sensitivity.