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Kristen Macuga, Scott Frey; Tool use and representations of reachable space in the superior parietal lobe. Journal of Vision 2014;14(10):306. doi: 10.1167/14.10.306.
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© ARVO (1962-2015); The Authors (2016-present)
Monkey electrophysiology suggests that manipulating distant objects with a stick induces a remapping of extrapersonal (out of reach) into peripersonal (within reach) space. Neuropsychological research has shown that when parietal patients with peripersonal neglect point with a stick, their impairment extends into extrapersonal space. This remapping does not occur when a laser pointer is used, presumably because, unlike the stick, it is ineffective at manipulating the distant environment. fMRI evidence suggests that superior-parietal occipital cortex (SPOC) codes peripersonal space. If SPOC codes objects within reach (regardless of distance), then it should show increased activity when performing with a tool that can affect distant objects (stick) vs. a tool that cannot affect distant objects (laser pointer). In an attempt to clarify this issue, objects in our fMRI-based reciprocal aiming task were always presented beyond reach of the hand, and participants used either a stick or laser pointer matched for torque and dynamics. Movement time (MT) was analyzed along with the BOLD responses as a function of the index of difficulty (ID). We found that MT increased linearly with ID, thus obeying Fitts law. MTs did not differ between the stick and laser pointer, nor was there an interaction between tool type and MT suggesting that, although differing in their end-effector properties, the dynamics of our stick and laser pointer were well matched. However, we failed to find support for the hypothesis that SPOC is involved in representing reachable space. Instead, anterior superior parietal lobe responded selectively for actions performed with a stick, which physically extended the participants reach, as opposed to a laser pointer, which did not. We suggest that this region of the human brain supports dynamic representations of reachable space.
Meeting abstract presented at VSS 2014
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