EFFECTS OF OBJECT TEXTURE ON PRECONTACT MOVEMENT TIME IN HUMAN PREHENSION

Using kinematic data in a precision-grip reaching task, Weir, MacKenzi e, Marteniuk, and Cargoe (1991) concluded that prior to contact with a n object, its texture does not affect the course of grasping. The pres ent study used their task of reaching for and lifting a slippery-, nor mal-(polished metal), or rough-surfaced dowel. This occurred under the original, blocked condition, in which textures were held constant wit hin a series of trials, and under a new, randomized condition, in whic h textures varied randomly from trial to trial. Performance was also e xamined over more extended periods of practice. Reaction time and prec ontact movement time were directly measured. In contrast to the result s of Weir et al., 1991, reaching for the slippery dowel resulted in sl ower movement time. This effect was found both early and late in pract ice for the randomized condition; it was found only in late practice f or the blocked condition. These effects can be attributed to the great er geometric and dynamic precision required for lifting a slippery obj ect.