EFFECTS OF OBJECT TEXTURE ON PRECONTACT MOVEMENT TIME IN HUMAN PREHENSION

Using kinematic data in a precision-grip reaching task, Weir, MacKenzie, Marteniuk, and Cargoe (1991) concluded that prior to contact with an object, its texture does not affect the course of grasping. The present study used their task of reaching for and lifting a slippery-, normal-(polished metal), or rough-surfaced dowel. This occurred under the original, blocked condition, in which textures were held constant within a series of trials, and under a new, randomized condition, in which textures varied randomly from trial to trial. Performance was also examined over more extended periods of practice. Reaction time and precontact movement time were directly measured. In contrast to the results of Weir et al., 1991, reaching for the slippery dowel resulted in slower movement time. This effect was found both early and late in practice for the randomized condition; it was found only in late practice for the blocked condition. These effects can be attributed to the greater geometric and dynamic precision required for lifting a slippery object.