Geometric features of workspace and joint-space paths of 3D reaching movements Mary D. Klein Breteler a, * , Ruud G.J. Meulenbroek a , Stan C.A.M. Gielen b a Department of Experimental Psychology, University of Nijmegen, Nijmegen, The Netherlands b Department of Medical Physics and Biophysics, University of Nijmegen, Nijmegen, The Netherlands Received 15 November 1997; received in revised form 15 May 1998; accepted 7 June 1998 Abstract The present study focuses on geometric features of workspace and joint-space paths of three-dimensional reaching movements. Twelve subjects repeatedly performed a three-seg- ment, triangular-shaped movement pattern in an approximately 60° tilted horizontal plane. Task variables elicited movement patterns that varied in position, rotational direction and speed. Trunk, arm, hand and ®nger-tip movements were recorded by means of a 3D motion- tracking system. Angular excursions of the shoulder and elbow joints were extracted from position data. Analyses of the shape of 3D workspace and joint-space paths focused on the extent to which the submovements were produced in a plane, and on the curvature of the central parts of the submovements. A systematic tendency to produce movements in a plane was found in addition to an increase of ®nger-tip path curvature with increasing speed. The ®ndings are discussed in relation to the role of optimization principles in trajectory-formation models. Ó 1998 Elsevier Science B.V. All rights reserved. PsycINFO classi®cation: 2330 Keywords: Motor co-ordination; Shoulder; Hand Acta Psychologica 100 (1998) 37±53 * Corresponding author. Nijmegen Institute for Cognition and Information, P.O. Box 9104, 6500 HE Nijmegen, The Netherlands. Fax: +31 24 3616066; e-mail: kleinbreteler@nici.kun.nl 0001-6918/98/$ ± see front matter Ó 1998 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 1 - 6 9 1 8 ( 9 8 ) 0 0 0 2 4 - 9