April 24, 2008 Time: 3:27am t1-v1.0 UNCORRE C TED PROOF Review of Models for the Generation of Multi-Joint Movements in 3-D Stan Gielen Abstract Most studies in motor control have focused on movements in two dimensions and only very few studies have systematically investigated move- ments in three dimensions. As a consequence, the large majority of modeling studies for motor control have tested the predictions of these models using movement data in 2D. As we will explain, movements in 3D cannot be under- stood from movements in 2D by adding just another dimension. The third dimension adds new and unexpected complexities. In this chapter we will explore the frames of reference, which are used in mapping sensory information about movement targets into motor commands and muscle activation patterns. Moreover, we will make a quantitative comparison between the predictions of various models in the literature with the outcome of 3D movement experiments. Quite surprisingly, none of the existing models is able to explain the data in different movement paradigms. Introduction The process of moving the hand to a target in space is a complex process, which involves a series of sensorimotor transformations that translate visual and other sensory information about the location of a target and the limbs into a set of motor commands that bring the hand to the desired position. This series of transformations is not simply a sequence of serial information processing stages. Rather, behavioral, neurophysiological and clinical studies have revealed several parallel pathways to implement these sensorimotor processes. Motor control or action cannot be clearly distinguished from perception. Perception of an object precedes any goal-directed action. At the other hand, perception is an active process, which requires movements to improve the accuracy and reliability of perception. For example, when we want to explore S. Gielen Department of Biophysics, Radboud University Nijmegen, Geert Grooteplein 21, 6525 EZ Nijmegen, The Netherlands e-mail: S.Gielen@science.ru.nl 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 D. Sternad (ed.), Progress in Motor Control, DOI: 10.1007/978-0-387-77064-2_28, Ó Springer ScienceþBusiness Media, LLC 2008 521