Time, touch and temperature affect perceived finger position and ownership in the grasp illusion

Abstract

Perceived body position and ownership are fundamental to our ability to sense and interact with the world. Previous work indicates that temporally congruent, repetitive multisensory stimuli are needed to alter the sense of body ownership. In the present study 30 subjects passively grasped an artificial rubber finger with their left index and thumb while their right index finger, located 12 cm below, was lightly clamped. Fingers with varied physical characteristics were also passively grasped to determine how these characteristics influenced perceived body position and ownership. Subjects immediately felt their hands to be 5.3 cm [3.4 to 7.3] (mean [95%CI]) closer, a feeling that remained after 3 min (6.0 cm [4.5 to 7.5]). By the end of the trial, perceived ownership increased by 1.2 [0.6 to 1.9] points on a 7-point Likert scale, with the group average moving from 'neither agree or disagree' at the start to 'somewhat agree' at the end. Compared to grasping a control rubber finger, grasping a cold, rough, oddly shaped or rectangular shaped finger-like object reduced perceived ownership. These results provide new insights into the role of cutaneous sensory receptors in defining these aspects of proprioception, and the speed with which these effects occur. Static touch rapidly induces large, sustained changes in perceived body position and prolonged exposure to these cutaneous inputs, alone, can induce a sense of body ownership. Also, certain physical characteristics of grasped objects influence the sense of body ownership.

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