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Hunter Schone, Roni Maimon Mor, Chris Baker, Tamar Makin; Expert tool users do not visually embody their hand-held tool. Journal of Vision 2020;20(11):777. doi: https://doi.org/10.1167/jov.20.11.777.
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The idea that when we use a tool we incorporate it into our body representation (‘embodiment’) has been a major inspiration for science and innovation. Here, we use the visual hand representation to test the tool embodiment theory. Previous work has shown that amputees that use a prosthetic hand represent their own prosthesis more dissimilarly to real hands in visual cortex, compared to controls, challenging current views of prosthesis/tool embodiment (Maimon-Mor & Makin, 2020). It remains unclear, however, whether this is a common representational feature of expert use for any tool. We investigated whether able-bodied expert tool users visually embody their expert tool (e.g. represented more like a hand), compared to novices. We used Representational Similarity Analysis of fMRI data from 7 expert litter pickers and 12 novices. Participants viewed first-person grasping videos of hands, litter pickers and a non-expert grasping tool in an event-related design. A region of interest in occipitotemporal cortex (OTC) was independently localized by contrasting action videos of hands and tools vs. objects and abstract visual information, acquired on independent data. We found that expert tool users represent their expert tool more dissimilarly to hands, compared to novices (t(18)=-3.202, p = .005). Instead, expert tool users represent both grasping tools (expert and non-expert) more similarly to each other, compared to novices (t(18)=-2.271, p = .009). Like the expert tool, experts also represent the non-expert grasping tool more dissimilarly to hands, compared to novices (t(18)=2.948, p = .036). Together with our previous findings in prosthesis users, our results suggest that expert tool use, be it a prosthesis or a hand-held tool, leads to greater dissociation of the tool from the visual hand representation. Furthermore, our findings extend previous evidence for experience-dependent plasticity of functional representations in OTC.
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