PARALLEL DIRECTION AND EXTENT SPECIFICATION OF PLANAR REACHING ARM MOVEMENTS IN HUMANS

The present study was undertaken to clarify further whether the progra mming of direction and extent of the same motor trajectory is accompli shed by parallel or serial processing channels. We reasoned that if di rection and distance are independently specified, then the time course of each process should not be influenced by the need for simultaneous ly specifying the other parameter. If direction and distance are speci fied in a serial order, the need to specify two parameters rather than only one should prolong the process of response specification. For th is purpose experiments were run on the same six subjects, using our ti me-response paradigm and the data obtained were compared. To avoid any possible effect attributable to the Hick and Hyman law, the number of targets was maintained invariant and equal to four. Our major finding is that the time course of directional specification of reaching move ments is not influenced by the need for simultaneously specifying exte nt. This is consistent with our view of parameterization of planning a nd executing movements, in which the two parameters (direction, extent ) can be specified in parallel. Copyright (C) 1996 Elsevier Science Lt d.