Distorted Body Representations in Healthy Cognition

Abstract

Delusions and misperceptions about the body are a conspicuous feature of numerous neurological and psychiatric conditions. In stark contrast to such pathological cases, the immediacy and familiarity of our ordinary experience of our body can make it seem as if our representation of our body is highly accurate, even infallible. Recent research has begun to demonstrate, however, that large and systematic distortions of body representation are a normal part of healthy cognition. Here, I will describe this research, focusing on distortions of body representations underlying tactile distance perception and position sense. I will also discuss evidence for distortions of higherorder body representations, such as the conscious body image. Finally, I will end with a discussion of the potential relations among different body representations and their distortions. Distortions of Body Representations 3Our body is the core of our sense of self, and central to our personal identity as an individual. We experience our body from the outside, as a physical object in the world like any other, but also from the inside, as an object of immediate experience (Bermúdez, Marcel, & Eilan, 1995). The intimate and direct connection we have with our own body can make knowledge of our body seem immune to the usual sources of perceptual error and illusion. Indeed, the very fact that we have multiple ways of knowing about our body (from inside, and from outside) could very well contribute to making the overall perception of the body highly reliable. While distortions and misperceptions of the body are a familiar result of several psychiatric and neurological conditions, it is natural to suppose that healthy adults have highly accurate -even infallible -knowledge about the physical structure of their bodies. In this paper, I will describe recent research that has begun to question this assumption, showing large and systematic distortions of body representation in healthy adults. After giving a brief summary of the varied distortions of body representation found in pathological conditions, I will describe research showing large distortions of body representations

No Correlation between Distorted Body Representations Underlying Tactile Distance Perception and Position Sense

“…For example, the overestimation of hand width relative to length mirrors findings of greater tactile spatial acuity in the medio-lateral than in the proximo-distal axis of the limbs (e.g., Weber, 1834/1996; Cody et al, 2008) and the fact that receptive fields of neurons in the spinal cord and cortex representing the limbs tend to be oval-shaped, with the long axis running along the proximo-distal limb axis (e.g., Powell and Mountcastle, 1959; Brooks et al, 1961; Brown et al, 1975; Alloway et al, 1989). Distortions in both tactile distance perception and position sense, however, are much smaller than would be predicted on the basis of receptive field size alone (Taylor-Clarke et al, 2004; Longo, 2017), suggesting that low-level distortions are at least partly corrected before affecting tactile distance perception and position sense. Thus, one possibility is that body representations underlying tactile distance perception and position sense are completely distinct, but both are shaped by lower-level somatosensory maps, and inherit their distortions.…”

Perceived face size in healthy adults

“…It has been assumed that healthy people have accurate body representations and only very recently has research begun to challenge this assumption [5,11,32,33,35,54–56]. While these studies have started to explore body size perception, only a few studies have looked specifically at the face or head.…”

Mapping the internal geometry of tactile space.

“…Touch, however, can clearly also be used to perceive the extrinsic physical properties of objects. Longo, Azañón, and Haggard (2010) argued that perceiving the metric properties of objects touching the skin requires that immediate sensory signals be combined with (Berryman, Yau, & Hsiao, 2006), sounds produced by action (Tajadura-Jiménez et al, 2012, 2015, the rubber hand illusion (Bruno & Bertamini, 2010), and tool use (Canzoneri et al, 2013;Miller, Longo, & Saygin, 2014, 2017. Thus, in analogy with the modulation of perceived passability of apertures when apparent eyeheight was altered shown by Warren and Whang (1987), these results show that experimental manipulations of represented body size alter perceived tactile distance.…”

“…In owl monkeys, for example, the magnification levels on different skin surfaces differ by two orders of magnitude (e.g., Sur, Merzenich, & Kaas, 1980). While the differences in perceived tactile distance across skin surfaces seen in Weber's illusion parallel these differences, they are dramatically smaller in magnitude (Taylor-Clarke et al, 2004;Longo, 2017).…”