Dissociable effects of irrelevant context on 2D and 3D grasping.

Grasping movements directed toward real objects are typically unaffected by irrelevant aspects of the object and its surroundings, indicating that such interactions are based on analytic processing of object shape and size. However, recent findings show that grasping directed toward two-dimensional (2D) objects is subjected to perceptually mediated effects of relative shape and size. It is unclear however, whether context-dependent processing-a hallmark of visual perception-affects 2D grasping in the same fashion. Here, we explored this possibility by comparing the influence of a newly discovered contextual effect on 2D and on 3D grasping. According to the range of standard effect (RSE), the perceptual resolution for a stimulus depends on the range of the other stimuli presented within the same session, with higher resolution obtained under narrow compared to wide context range. In two experiments, participants were asked to grasp 3D and 2D objects embedded in a wide or a narrow range. The results showed that, unlike 3D grasping, which was immune to contextual information, the resolution during 2D grasping was significantly modulated by the range of the irrelevant context. The findings suggest that visuomotor control directed to 2D objects is intruded by irrelevant perceptual information, making it context-dependent.