The Extent of Skin Bending Rather Than Action Possibilities Explains Why Holes Feel Larger With the Tongue Than With the Finger


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Abstract

When small holes are felt with the tongue, they are perceived to be larger compared with when felt with the index finger. This oral illusion has not yet been consistently explained. From present action-specific accounts of perception, we derived a high-level sticking-action hypothesis to explain the oral illusion. In 5 experiments, we contrasted this hypothesis’ predictions with predictions from the low-level bending hypothesis, which states that felt hole size decreases with decreasing bending of the skin at the hole’s edges. Results from Experiments 1 to 3 showed that felt hole size decreases with the pliability of the exploring effector (tongue > index finger > big toe, big fingers > small fingers), which affects skin bending, and that size perception with the highly pliable tongue is more accurate than with the less pliable finger and toe. Experiment 4 showed that holes of intermediate size are perceived to be larger with the tongue’s tip than with its dorsum. Finally, exploration styles that lessen the skin’s bending (using low vs. high tongue forces in Experiment 5) decreased perceived hole size. Overall, the results favor the low-level bending hypothesis over the high-level sticking-action hypothesis.

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