Abstract
Heaviness perception involves a misperception of weight known, since the 19th century, as the Size-Weight Illusion ^1^. The larger of two objects of equal mass is reported to be lighter than the smaller when they are lifted. The illusion has been found to be reliable and robust. It persists even when people know that the masses are equal and handle objects properly ^2^. It has been exhibited by children of only 2 years of age ^3,4^. All this suggests that the effect might be intrinsic to humans. Although different hypotheses have been advanced to account for the illusion over the 100+ years it has been studied ^5-11^, its origin remains unknown. More recently, people's perception of optimal objects for long distance throwing was found to exhibit a size-weight relation similar to the illusion ^12,13^, greater weights were picked for larger objects and they were indeed thrown to the greatest distances. Here we show that the perception of heaviness (including the illusion) and perception of optimal objects for long distance throwing are in fact equivalent. Thus, the size-weight illusion has a useful application: optimal objects for throwing are picked by a thrower as having a particular heaviness, which is the best heaviness learned when learning to throw ^14,15^. Long distance throwing is a uniquely human ability that is understood to have enabled our species to survive and even thrive during the ice ages ^16-22^. The fact that the illusion is a functional component of human throwing skill adds credence to the idea that it is intrinsic to the species.
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Zhu, Q., Bingham, G. The Size-Weight Illusion Is Not an Illusion When Picking the Best Objects to Throw. Nat Prec (2010). https://doi.org/10.1038/npre.2010.4584.1
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DOI: https://doi.org/10.1038/npre.2010.4584.1