acta psychologica ELSEVIER Acta Psyehologica92 (1996) 17-32 Visuomotor control when reaching toward and grasping moving targets Heather Carnahan a, ,, Bradford J. McFadyen b a Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada b D~partement de Kinanthropologie, Universit~ du Quebec ~ Montreal, Montreal, Quebec H3C 3P8, Canada Received 25 January 1994; revised 6 January 1995; accepted 7 February 1995 Abstract Two experiments were conducted to examine the influence of target motion on the control and coordination of reaching and grasping movements. In Experiment 1 all the measures which reflected the transport or reaching phase of prehension (movement time, peak velocity, time to peak velocity, and transport tau margin) were sensitive to the velocity of the target, with subjects moving even slower than during the stationary trials, when the target was moving very slowly. Measures which reflected grasp formation such as the size of maximum aperture and the grasping tau margin were not influenced by target speed. To further investigate this dissociation between grasp and transport, different object sizes and even slower object speeds were introduced in Experiment 2. Transport results similar to those found in the first study were observed. However, in Experiment 2, both size of peak aperture and the grasping tau margin were sensitive to target movement. The results of these two studies are discussed in terms of the limitations of optic variables in the visual regulation of movement, and the independence of the control of the reach and grasp phases of prehension. PsyclNFO classification: 2330 Keywords: Prehension;Moving targets; Visuomotorcontrol 1. Introduction Grasping or catching moving objects is something that we are all very good at, even as babies (von Hofsten, 1980, 1983). However, a closer examination of this seemingly * Corresponding author. E-mail: carnahan@healthy.uwaterloo.ca, Fax: + 1 519 746-6776, Tel.: + 1 519 885-1211. 0001-6918//96/$15.00 © 1996 Elsevier Science B.V. SSDI 0001-6918(95)00006-2