Touching Curvature and Feeling Size: a Contrast Illusion

in Multisensory Research
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We know that our eyes can be deceiving. Here we demonstrate that we should not always trust our sense of touch either. Previous studies have shown that when pinching an object between thumb and index finger, we can under many circumstances accurately perceive its size. In contrast, the current results show that the local curvature at the areas of contact between the object and the fingers causes systematic under- or overestimation of the object’s size. This is rather surprising given that local curvature is not directly related to the object’s size. We suggest an explanation in terms of a contrast between the finger separation and an inferred relationship between local curvature and size. This study provides the first demonstration of an illusory haptic size percept caused by local curvature in a pinch grip.

Multisensory Research

A Journal of Scientific Research on All Aspects of Multisensory Processing



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  • (a) Categorical means of minor and major axis comparisons averaged over participants. The dashed line indicates chance level and error bars indicate the between subjects standard error (SE). (b) Proportion of reference-larger responses as a function of the aspect ratio plotted on a log scale. Aspect ratio was calculated as the length of the axis that had to be estimated divided by the length of the other axis. This means that negative aspect ratio differences relate to minor axis comparisons and positive ones to major axis comparisons. Error bars indicate the between subjects standard deviation (SD).

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