Constraint Hierarchies for Human Reaching
Open Access
- Author:
- Coelho, Chason Joseph
- Graduate Program:
- Psychology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 09, 2013
- Committee Members:
- David A. Rosenbaum, Dissertation Advisor/Co-Advisor
David A. Rosenbaum, Committee Chair/Co-Chair
Robert L Sainburg, Dissertation Advisor/Co-Advisor
Robert L Sainburg, Committee Chair/Co-Chair
Richard Alan Carlson, Committee Member
Byron C Jones, Committee Member - Keywords:
- human motor control
cognitive psychology
biomechanics
action selection
handedness
end-state comfort - Abstract:
- In the work reported in this thesis, I sought to understand how individuals select particular actions when more than one can achieve the task at hand. My approach to studying this degrees-of-freedom problem was to identify body- and task-related features that help constrain the alternatives. The current work addressed the understudied issues of whether and how actions depend on multiple constraints in any given task. Thus, the overarching goal of the present research was to test the notion that individuals select actions with respect to multiple constraints that are cognitively ranked by their values for meeting task demands. To pursue this idea, I conducted a series of experiments that pertained to the prominent preference to use the right hand for unimanual tasks. This hand preference likely serves as a common constraint, but surprisingly little research has described it in such a fashion. It is perhaps unsurprising, then, that little research has tested the relative priority of hand preference with other known constraints. The experiments reported here were meant to fill this void. The first experiment showed that right-handed people make hand choices that are related to, and may therefore depend upon, interlimb control asymmetries that lead to distinct ways of completing point-to-point reaches. However, choices were not related only to these interlimb sensorimotor performance asymmetries but also depended on other workspace location constraints. These findings support the idea that action choices depend on constraints that are ranked for each task. The second experiment extended this idea to unimanual object transport tasks. I gave right-handed people choices between moving objects in ways that either satisfied hand preference or the well-known tendency to end transports in comfortable arm postures. This experiment tested three specific hypotheses. One was that hand preference is weighted more heavily than comfort. The associated prediction was that participants would use the right hand even when doing so led to uncomfortable postures. Another hypothesis was that comfort is weighted more heavily than hand preference. The associated prediction was that participants would use whichever hand afforded comfortable ending postures. The third hypothesis was the only logical alternative -- that people do not prioritize hand preference and comfort. This hypothesis predicted that participants would not consistently satisfy hand preference or comfort. The results showed that participants almost always used the hand that afforded comfortable ending postures, suggesting that aiming-related comfort outranks hand preference for the types of object transports I tested. The third experiment explored the flexibility of this weighting by manipulating task demands. The results showed that the magnitude of this priority can be attenuated by more heavily weighting hand preference. However, the priority is not reversed or eliminated in this case. The final experiment tested the idea that the priority that comfort has over hand preference also reflects considerations of performance. This hypothesis predicted that comfortable postures would afford better performance at the end of the transport than uncomfortable postures and that the right hand would afford better performance than the left hand. The most important prediction, however, was that the performance advantage of comfortable postures over uncomfortable postures would be greater than the performance advantage of the right over the left. The results bore out these predictions, again supporting the idea that manual action choices depend on hierarchies of constraints that are weighted in accordance with the demands of the task.