Implicit spatial representation of objects and hand size

A Saulton, S de la Rosa, H Bülthoff

Department Perception, Cognition and Action, Max Planck Institute Biological Cybernetics, Germany
Contact: aurelie.saulton@tuebingen.mpg.de

Recent studies have investigated the body representation underlying tactile size perception and position sense. These studies 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]. Here, we are interested in whether the observed distortions are specific to the hand or can be also detected with objects (star, box, rake, circle). Participants judged the location in external space of predefined landmarks on the hand and objects. We compared the actual and estimated horizontal and vertical distances between landmarks. Our results replicate previously reported significant underestimations of the finger length (vertical axis). There was no significant overestimation of the hand width. In the case of objects, we found a significant underestimation along the vertical axis for all objects (p<0.01), which was smaller than for the hand (p<0.05). There was no significant distortion along the horizontal axis for the star. We observed significant horizontal underestimations for the circle and the box, and a significant overestimation for the rake (p<0.05). In summary, distortions along the vertical axis also occur for objects. However, the size of the vertical distortion was larger for the hand than for the objects.

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