Currently, it is known that the size of an object influences how heavy it feels (i.e., the size-weight illusion). However, it remains uncertain whether the same applies to the body. Elisa Raffaella Ferrè and colleagues conducted an experimental study to investigate how embodying various hand sizes affects the perception of hand weight. Hand size was manipulated using a visual-tactile illusion with magnifying and minifying mirrors. The results showed that the perception of hand weight is flexible and easily altered by the perception of hand size. However, the perceived weight of the hand is invariably underestimated. Although a larger hand feels heavier, while a smaller hand feels lighter, there is still an underestimation of the actual weight of the hand in both conditions. This also contrasts with object perception, where larger objects feel lighter when compared to smaller objects of the same weight. Given that individuals with anorexia nervosa, for example, often experience their bodies as objects, these findings may help deepen our understanding of such disorders and their connection to bodily distortions. This study was supported by the BIAL Foundation, in the scope of the research project 41/20 - Luminous dancing fairies in weightlessness: How gravity shapes conscious experiences, and published in the journal Cognition, in the article Perceived hand size and perceived hand weight.
ABSTRACT
The dimensions of objects and our body parts influence our perception of the weight of objects in our surroundings. It has been recently described a dramatic underestimation of the perceived weight of the hand. However, little is known on how perceived size informs the perceived weight of our own body parts. Here we investigated the effects of embodying an enlarged and a shrunken hand on perceived hand weight. We manipulated hand size using a visual-tactile illusion with magnifying and minifying mirrors. We then measured perceived hand weight using a psychophysical matching task in which participants estimate if a weight hanged on their wrist feels heavier or lighter than the experienced weight of their hand. Our results indicated that participants tended to underestimate the weight of their hand more when embodying a smaller hand, and less so when embodying a larger hand. That is, the perceived size of the hand plays a role in shaping its perceived weight. Importantly, our results revealed that the perception of the weight of body parts is processed differently from the perception of object weight, demonstrating resistance to the size-weight illusion. We suggest a model based on constant density to elucidate the influence of hand size in determining hand weight.
