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Hugo Bruggeman, Christine L Eid, John J Rieser, Herbert L Pick; Alteration of the direction of throwing; multiple levels of adaptation. Journal of Vision 2003;3(9):678. doi: 10.1167/3.9.678.
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Movements are organized at multiple levels, including that of muscles & joints, space, and functional actions. Adaptation paradigm studies offer a method to investigate such organization. Typically, these studies are limited to the former two levels by altering either the motor system (e.g. change in force field), or the visual system (e.g. displacement of the visual field). To investigate movement organization at the functional action level, we induce perceptual learning by altering the perceptual event. For example, walking on a moving belt alters the perceptual event for translatory locomotion. Adaptation to such context transfers to functionally equivalent movements such as sidestepping, but not to other leg movements such as turning by stepping in place (Rieser et al., 1995).
Other studies altered the perceptual event for the direction of hurling movements; participants are seated on the periphery of a rotating carousel and throw underhanded at a directly opposite target. In this context, adaptation reliably alters the direction of underhand throwing from a static position on the ground. This negative aftereffect transfers to functionally equivalent movements such as overhand throwing.
Besides altering the perceptual event, throwing while seated on a turning carousel likely alters the forces that act upon the arm. This paper presents a series of studies that tease apart the relative contribution of adaptation to such forces and to the perceptual event.
Adaptation to throwing on the turning carousel results in a negative aftereffect in the direction of throwing, which has an initial magnitude of 5.1 degrees. This decays over test trials to an asymptote of 3.8 degrees. Subsequent experiments suggest that the decay is due to readaptation over time of the force contribution while the perceptual event adaptation remains constant. These results will allow future studies to pursue a more detailed investigation of the multiple levels of movement organization.
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