Tool morphology constrains the effects of tool use on body representations.

Abstract

What factors constrain whether tool use modulates the user's body representations? To date, studies on representational plasticity following tool use have primarily focused on the act of using the tool. Here, we investigated whether the tool's morphology also serves to constrain plasticity. In 2 experiments, we varied whether the tool was morphologically similar to a target body part (Experiment 1, hand; Experiment 2, arm). Participants judged the tactile distance between pairs of points applied to their tool-using target body surface and forehead (control surface) before and after tool use. We applied touch in 2 orientations, allowing us to quantify how tool use modulates the representation's shape. Significant representational plasticity in hand shape (increase in width, decrease in length) was found when the tool was morphologically similar to a hand (Experiment 1A), but not when the tool was arm-shaped (Experiment 1B). Conversely, significant representational plasticity was found on the arm when the tool was arm-shaped (Experiment 2B), but not when hand-shaped (Experiment 2A). Taken together, our results indicate that morphological similarity between the tool and the effector constrains tool-induced representational plasticity. The embodiment of tools may thus depend on a match-to-template process between tool morphology and representation of the body.

Implicit body representations and tactile spatial remapping

“…These results suggests that tactile spatial remapping relies on a representation of the hand which is fatter than actual hand shape, consistent with results reported previously for position sense , 2012aLongo et al, 2012) and tactile size perception (Canzoneri et al, 2013;Green, 1982;Le Cornu Knight et al, 2014;Longo & Sadibolova, 2013;Miller, Longo, & Saygin, 2014). 1.…”

Mapping the internal geometry of tactile space.

“…Touch, however, can clearly also be used to perceive the extrinsic physical properties of objects. Longo, Azañón, and Haggard (2010) argued that perceiving the metric properties of objects touching the skin requires that immediate sensory signals be combined with (Berryman, Yau, & Hsiao, 2006), sounds produced by action (Tajadura-Jiménez et al, 2012, 2015, the rubber hand illusion (Bruno & Bertamini, 2010), and tool use (Canzoneri et al, 2013;Miller, Longo, & Saygin, 2014, 2017. Thus, in analogy with the modulation of perceived passability of apertures when apparent eyeheight was altered shown by Warren and Whang (1987), these results show that experimental manipulations of represented body size alter perceived tactile distance.…”

Distorted Body Representations in Healthy Cognition

“…Other recent research has shown that perceived tactile distance is expanded across joint boundaries, showing that the high-level segmentation of the body into discrete parts produces categorical perception effects on tactile distance (de Vignemont, Majid, Jola, & Haggard, 2009;Le Cornu Knight, Longo, & Bremner, 2014). Finally, two recent studies have shown that tool-use, which can be thought of as extending arm size, also produces systematic changes to tactile distance perception (Canzoneri et al, 2013;Miller, Longo, & Saygin, 2014).…”