Sequential Effects in Reaching Around Obstacles

Open Access
- Author:
- Jax, Steven Andrew
- Graduate Program:
- Psychology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 22, 2004
- Committee Members:
- David A. Rosenbaum, Committee Chair/Co-Chair
Rick Owen Gilmore, Committee Member
Cathleen M Moore, Committee Member
Robert L Sainburg, Committee Member - Keywords:
- reaching
movement planning
motor control
obstacle
obstacle avoidance - Abstract:
- Many models of human reaching propose that movements are planned by minimizing movement costs. A common assumption of these models is that movements are planned anew each time one is desired. In this thesis I will suggest that movement planning instead relies on the reuse and modification of previous movement plans. One prediction that follows from this proposal is that the ability to minimize movement costs may be limited by the perceptual- motor system’s ability to modify the reused plan. The results from five experiments in which participants performed reaching movements in the presence of or in the absence of an intervening obstacle support this prediction. When both movement types were required within a block, direct movements were more curved when preceded by obstacle–avoiding movements than by other direct movements. Thus, the cost of performing a direct movement was not fully minimized when its path differed significantly from the previous trial’s path. In addition, obstacle-avoiding movements were less curved when preceded by direct movements than by other obstacle-avoiding movements. This second finding provides additional evidence for the reuse of previous movement plans. In general, the sequential effects suggested that the perceptual–motor system reused a relatively high–level hand path representation that could be translated to other regions of space. Further experiments showed that the observed sequential effects were not anticipatory in nature, that they persisted for many trials, and that they were reduced when the time between movements was increased or when participants were instructed to move as straight as possible when no obstacle appeared. Collectively, the results show that physical movement costs may not always be minimized if computational demands favor the reuse of movement plans. This outcome contradicts current models of motor control which assume physical cost minimization.