Implicit body representations and the conscious body image

Matthew R Longo,Patrick Haggard

doi:10.1016/j.actpsy.2012.07.015

Matthew R Longo, Patrick Haggard

Open Access

https://doi.org/10.1016/j.actpsy.2012.07.015

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Abstract

Recent studies have revealed that somatosensory processing relies on a class of implicit body representations showing large distortions of size and shape. The relation between these representations and the conscious body image remains unclear. Dissociations have been reported in the clinical literature on eating disorders between different body image measures, with larger and more consistent distortions found with depictive measures, in which participants compare their body to a visual depiction of a body, than metric measures, in which participants compare their body to some non-body standard. Here, we compared implicit body representations underlying position sense to the body image measured with both depictive and metric methods. The body image was measured using both a depictive method (template matching) in which participants judged whether their hand was wider or more slender than a shown hand picture, and a metric method (line length) in which participants judged whether different parts of their hand were shorter or longer than a presented line. Consistent with previous findings, characteristic distortions were found for the implicit body representation underlying position sense. These distortions were also found in attenuated form for metric – but not depictive – body image measures. While replicating the basic dissociation between implicit body representations and the conscious body image, these results demonstrate that this dissociation is not absolute and specific tasks may utilise both to varying degrees depending on task demands. Metric measures may not be pure measures of body image, but some combination of visual and somatosensory body representations.

Highlights

Several aspects of perception require that immediate sensory signals be combined with stored representations of body size and shape
Consistent with recent results (Longo & Haggard, 2010, 2012; Longo, Long, & Haggard, 2012), these results revealed that human position sense relies on a highly distorted hand representation
With a depictive task in which participants compared the shape of their hand to a hand picture, the body image appeared highly accurate, as in previous studies

Summary

Introduction

Several aspects of perception require that immediate sensory signals be combined with stored representations of body size and shape. We have recently investigated body representations underlying somatosensation, finding highly distorted representations of the hand underlying position sense (Longo & Haggard, 2010) and tactile size perception (Longo & Haggard, 2011). These distortions appear to maintain distortions characteristic of primary somatosensory maps in the brain (e.g., the ‘Penfield homunculus’). Recent results have revealed a striking dissociation between the (highly distorted) hand representation underlying somatosensory processing and the (largely veridical) body image when assessed with a depictive task (Longo & Haggard, 2010). As a metric measure of body image, participants saw lines and judged whether each was shorter or longer than part of their hand (Line length task) (Fig. 1)

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