Strength of the rubber hand illusion varies as a function of distance between seen and felt hand

Donna Lloyd, School of Psychological Sciences, The University of Manchester

Abstract
This study aimed to quantify the strength of the rubber hand illusion as a function of distance between touch seen on the rubber hand and touch felt on the person’s real hand. Fifty-two undergraduate students took part for course credit. On successive trials the rubber hand was moved to one of six unpredictable locations (order randomised between participants) from 17.5cm to 67.5cm. The rubber hand and the person’s real hand were then stroked simultaneously. Participants indicated when they experienced the illusion by the extent to which they agreed with the statement ‘it seemed as though I was feeling touch in the place where I saw the rubber hand touched’ on a scale of +3 to -3. Non-parametric tests (Friedman and Wilcoxin) revealed a highly significant effect of position of the rubber hand on strength of illusion (p < .001) with significantly more participants responding to the illusion (with a rating of +3 or +2) when the distance between the real and rubber hand was 17.5cm than when it was 27.5cm (62% vs. 50%; p = .016). These results indicate a direct relationship between the spatial disparity of visual and tactile inputs contributing towards the perceptual illusion and the strength of the illusion.

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