Aurelie Saulton

The nature of body representations in perception and action

Aurelie Saulton

Introduction

Accurate information about body structure and posture is fundamental for effective control of our actions. It is often assumed that healthy adults have accurate representations of their body. Although people’s abilities to visually recognize their own body size and shape are relatively good, the implicit spatial representation of their body is extremely distorted [1]. For instance, people’s tactile size perception of their hand is much larger in width and shorter in length than the actual size of the hand [2].

Goals

The aim of my research is to understand the nature of spatial distortions of the body. In particular, I investigate the perceptual-cognitive components contributing to distortions of implicit representation of the human hand.

Methods

To examine whether previously observed distortions only occur with the human body, I investigated whether similar distortions are observable with non-body items such as objects (Rake, post-it block and CD case). The distortions of the implicit spatial representation of these items were assessed with a localization task (see figure 1.A). I also assessed the explicit visual bias in perception of each item in a template matching task. The comparison of the distortions of the localization task and the template matching task reveals whether implicit spatial distortions are owed to a bias in explicit visual perception.

Initial results

Distortions in the localization task were found with both the hand and non-body items. No distortions were found in the visual template matching task. Interestingly the distortions measured on the objects in the localization task present a similar pattern of distortion to the one previously measured on the hand. This is especially the case of the rake who shares a similar structure to the human hand. Both the rake and the hand had slight overestimation of their width and an underestimation of their length. Moreover the distortions present on the rake were a significant predictor of the distortions measured on the human hand.

Initial conclusion

Overall, these results show that distortions of implicit spatial representations can be observed with body and non-body objects. These results have implications for theoretical accounts associating previously observed distortions with somatosensation: because localizing points on an object is unlikely to be aided by somatosensation, the assessed representations might reflect the contribution of other cognitive processes (e.g. visual spatial memory) to the distortion of the body model [3; 4].

References

1. Longo, M. R., & Haggard, P. (2010). An implicit body representation underlying human position sense. Proceedings of the National Academy of Sciences, 107(26), 11727–11732. doi:10.1073/pnas.1003483107

2. Longo, M. R., & Haggard, P. (2011). Weber’s illusion and body shape: Anisotropy of tactile size perception on the hand. Journal of Experimental Psychology: Human Perception and Performance, 37(3), 720–726. doi:10.1037/a0021921

3. Saulton A, de la Rosa S and Bülthoff H (August-2013): Implicit spatial representation of objects and hand size, 36th European Conference on Visual Perception (ECVP 2013), Bremen, Germany, Perception, 42(ECVP Abstract Supplement) 176.

4.Saulton A, Dodds T ,Bülthoff HH , and de la Rosa S.(2015). Objects exhibit body model like shape distortions. Experimental brain research (in press).