NEAR, FAR, OR IN BETWEEN - TARGET EDGES AND THE TRANSPORT COMPONENT OF PREHENSION

It is well known that during visually guided prehension movements the peak velocity of the arm is scaled for object distance (e.g., Gentiluc ci et al., 1991; Jakobson & Goodale, 1991; Servos, Goodale, & Jakobson , 1992). Those movements are being directed not to single points in sp ace, however, but rather to objects with extent. Thus, object distance must be computed relative to some particular point on the object. Whe ther that point corresponds to the location of a particular edge, for example, has not been clearly demonstrated. In the present study, subj ects (N = 9) were presented with a series of oblong blocks positioned at different locations. Peak velocity increased with object size for r eaches in which different-sized objects had their near edges lined up; in contrast, the peak velocities of reaches directed to objects of di fferent sizes did not differ when the far edges of the objects were li ned up. The present study, therefore, provided confirmation that subje cts calibrate the peak velocity of their reaches relative to the far e dge of a target object.