The toolish hand illusion: embodiment of a tool based on similarity with the hand

Abstract

A tool can function as a body part yet not feel like one: Putting down a fork after dinner does not feel like losing a hand. However, studies show fake body-parts are embodied and experienced as parts of oneself. Typically, embodiment illusions have only been reported when the fake body-part visually resembles the real one. Here we reveal that participants can experience an illusion that a mechanical grabber, which looks scarcely like a hand, is part of their body. We found changes in three signatures of embodiment: the real hand’s perceived location, the feeling that the grabber belonged to the body, and autonomic responses to visible threats to the grabber. These findings show that artificial objects can become embodied even though they bear little visual resemblance to the hand.

Mind over matter: Perceived phantom/prosthesis co-location contributes to prosthesis embodiment in lower limb amputees

“…This contradicts previous categorical operationalization of obstacle tolerance and obstacle shunning in the past (Jalavisto, 1950;Saetta et al, 2018). It might simply be that prostheses represent a special kind of obstacle, due to their visual and functional similarity to a real body part, which might affect an individuals' body representation differently compared to an obstacle lacking these features (cf., Cardinali et al, 2021;Tsakiris, Carpenter, James, & Fotopoulou, 2010). Thus, future studies should directly compare within-subjects phantom responses to different types of obstacles in order to evaluate the specificity of results.…”

How Action Shapes Body Ownership Momentarily and Throughout the Lifespan

“…Interestingly, visual changes that are accompanied by corresponding tactile changes are judged as belonging to the agent herself. This is the basic idea behind the rubber hand illusion and its various versions (e.g., Botvinick and Cohen, 1998 ; Armel and Ramachandran, 2003 ; Sanchez-Vives et al, 2010 ; Kalckert and Ehrsson, 2012 ; Ma and Hommel, 2015a , b ; Cardinali et al, 2021 ). In the original experiment by Botvinick and Cohen ( 1998 ), participants received brush strokes on their occluded hand while simultaneously watching a fake hand in front of them being stroked synchronously or asynchronously with their real hand.…”

“…In fact, it has been suggested by most studies that illusory (explicit) ownership cannot be experienced for non-corporeal objects at all (e.g., Tsakiris and Haggard, 2005 ; Tsakiris et al, 2010 ; Guterstam et al, 2013 ; Kalckert et al, 2019a ). There are a few noticeable studies from recent years which question this constraint which we will discuss in the section “Does Active Ownership Depend on Immediate Control Experience?” (e.g., Liepelt et al, 2017 ; Cardinali et al, 2021 ). Full-body illusions (e.g., Slater et al, 2010 ), a paradigm in which a complete virtual body is looked at by the participant which either receives (a)synchronous tactile stimulation with the participant or is (a)synchronously controlled by the participant, might provide the opposite end of a corporeal-to-non-corporeal continuum.…”

“…Such situations can, for example, occur with different kinds of tools which people basically know how to use but have not done so before. Cardinali et al ( 2021 ) tested this idea by also adapting the passive rubber hand illusion, but this time using a mechanical gripper instead of a rubber hand and a balloon as a control object. While neither object resembles body parts, the illusion was elicited in terms of proprioceptive drift, subjective ratings, and skin conductance response for the gripper but not the balloon (Experiments 1 and 3) even without previous use of the gripper (Experiment 2).…”

“…Without downregulation, actual interoceptive and exteroceptive effects can be integrated into these situations easily ( Figure 1A ). While this model is mainly designed to explain differences in ownership experiences with immediate control experiences, it can also account for the findings discussed previously that past control experience alone can in some cases elicit ownership experiences as well (Liepelt et al, 2017 ; Cardinali et al, 2021 ; Pfister et al, 2020 ). When presenting an object with which a high amount of control experience has been accumulated in the past, the interoceptive and exteroceptive effect codes associated with controlling this object might already be activated to a degree which leads to their integration without a need to perform the action.…”