The dynamics of coordinated reaching and grasping: Scanning prehension properly

Prehension is the act of coordinated reaching and grasping. S.A. Wallace, E. Stevenson, A. Spear, D.L. Weeks [Hum. Movement Sci, 13 (1994) 255-289] proposed to assess the stability of this coordination by scanning the dynamics of prehension. The scanning method proposed by these authors prompted participants to position their peak hand aperture at different locations along the trajectory. Comparing the actual performance with the required performance, Wallace and colleagues concluded that there was a single stable pattern of coordination, albeit different for each individual. Here, we show that the method developed by Wallace et al. (1994, loc. cit.), and later used by C. Button, S, Bennett, K. Davids [Hum. Movement Sci. 17 (1998) 801-820] was flawed. We propose two potential fixes to the method and report a replication of the original experiment, Interpretation of the data with a corrected scanning technique showed that the method does not seem to be able to result in an unambiguous and precise assessment of the locus of stability. (C) 2000 Elsevier Science B.V. All rights reserved.