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Abstract:
Stored representations of body size and shape as derived from somatosensation (body model) are considered to be critical components of perception and action. It is commonly believed that the body model can be measured using a localization task and be distinguished from other visual representations of the body using a visual template matching task. Specifically, localization tasks have shown distorted hand representations consisting of an overestimation of hand width and an underestimation of finger length [Longo and Haggard, 2010, PNAS,107 (26), 11727-11732]. In contrast, template matching tasks indicate that visual hand representations (body image) do not show such distortions [Longo and Haggard, 2012, Acta Psychologica, 141, 164-168]. We examined the specificity of the localization and visual template matching tasks to measure body related representations. Participants conducted a localization and template matching task with objects (box, post-it, rake) and their own hand. The localization task revealed that all items' dimensions were significantly distorted (all p <.0018) except for the width of the hand and rake. In contrast, the template matching task indicated no significant differences between the estimated and actual item's shape for all items (all p>0.05) except for the box (p<0.01) suggesting that the visual representation of items is almost veridical. Moreover, the performance across these tasks was significantly correlated for the hand and rake (p<.001). Overall, these results show that effects considered to be body-specific, i.e. distortions of the body model, are actually more general than previously thought as they are also observed with objects. Because localizing points on an object is unlikely to be aided by somatosensation, the assessed representations are unlikely to be mainly based on somatosensation but might reflect more general cognitive processes e.g. visual memory. These findings have important implications for the nature of the body image and the body model.
