Are tools truly incorporated as an extension of the body representation?: Assessing the evidence for tool embodiment

Action does not drive visual biases in peri-tool space

Observers experience visual biases in the area around handheld tools. These biases may occur when active use leads an observer to incorporate a tool into the body schema. However, the visual salience of a handheld tool may instead create an attentional prioritization that is not reliant on body-based representations. We investigated these competing explanations of near-tool visual biases in two experiments during which participants performed a target detection task. Targets could appear near or far from a tool positioned next to a display. In Experiment 1, participants showed facilitation in detecting targets that appeared near a simple handheld rake tool regardless of whether they first used the rake to retrieve objects, but participants who only viewed the tool without holding it were no faster to detect targets appearing near the rake than targets that appeared on the opposite side of the display. In a second experiment, participants who held a novel magnetic tool again showed a near-tool bias even when they refrained from using the tool. Taken together, these results suggest active use is unnecessary, but visual salience is not sufficient, to introduce visual biases in peri-tool space.

Knowing your boundaries: no effect of tool-use on body representation following a gather-and-sort task

Internal representations of the body have received considerable attention in recent years, particularly in the context of tool-use. Results have supported the notion that these representations are plastic and tool-use engenders an extension of the internal representation of the arm. However, the limitations of the literature underlying this tool embodiment process have not been adequately considered or tested. For example, there is some evidence that tool-use effects do not extend beyond simplistic tool-use tasks. To further clarify this issue, 66 participants engaged in a period of tool-augmented reaches in a speeded gather-and-sort task. If task characteristics inherent to simplistic tasks are relevant to putative embodiment effects, it was predicted that there would be no effect of tool-use on tactile distance judgments or forearm bisections. A Bayesian analysis found considerable support for the null hypothesis in both outcome measures, suggesting that some of the evidence for tool embodiment may be based in task characteristics inherent in the narrow range of tool-use tasks used to study them, rather than a tool incorporation process. Potential sources of influence stemming from these characteristics are discussed.

Perceiving multiple properties of a single person-probe-surface system

We performed three experiments to investigate the extent to which people can selectively perceive different properties of a person-probe-surface system, and the extent to which such abilities are supported by sensitivities to different (components of) invariant mechanical parameters. Participants probed a surface with a wielded object and attempted to perceive an exteroceptive property of the probe (whole length), an exproprioceptive property of the probe (partial length), and an exteroceptive property of the surface (distance). After controlling for potential confounds, we found that participants were able to selectively perceive each of these properties, and that in each case, such abilities were supported by sensitivity to distinct components of mechanical invariants. The results suggest that people can selectively attend to properties both across and within components of a person-probe-surface system and are discussed in the context of the invariant mechanical parameters that support this ability.