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Liana Brown, Robert Doole, Nicole Malfait; Spatial adaptation following tool use. Journal of Vision 2009;9(8):713. doi: 10.1167/9.8.713.
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Hand-related visual-tactile (bimodal) cells have visual receptive fields (vRFs) that overlap and extend moderately beyond the skin of the hand. Electrophysiological evidence suggests, however, that this vRF will grow to encompass a hand-held tool following active tool use but not after passive holding (Iriki et al., 1996). Why does active tool use, and not passive holding, lead to vRF adaptation? One possibility is that vRF adaptation depends on motor adaptation: before a tool can be considered functional, the motor system must learn to predict and control the tool's motion in response to forces applied both by gravity and the actor. Another possibility is that vRF adaptation depends on visual adaptation: active tool use allows the user to see the length and capabilities of the tool. We tested these hypotheses by isolating visual training from motor training. Participants made speeded pointing movements to visible targets with a novel, weighted tool. Participants in the active training group performed self-generated actions. Active training provided both motor and visual experience with the tool. Participants in the passive training group were moved passively to each target by an experimenter. Passive training provided visual experience with the tool, but no motor experience. Finally, a no-training control group received no visual or motor tool-related experience. After training, we varied whether the tool was placed near or far from the target display and measured how quickly participants detected targets using a modified cueing paradigm. The active training group detected the target more quickly than other groups, and the active group was faster when the tool was placed near, rather than far from the target display. This tool location difference was not present for either the passive-training or control groups. These results suggest that motor learning influences how visual space around the tool is represented.
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