Weights in Visuo-Haptic Softness Perception are not Sticky
The contribution of vision to visuo-haptic softness judgments has been observed to be non-optimal and it has been speculated that the visual weights are “sticky”, i.e., do not account for the senses’ reliabilities [1, 2]. The present study tested the hypothesis of sticky weights by varying the quality of the visual information. Participants discriminated between the softness of two objects with deformable surfaces using only visual, only haptic, or bisensory information. Visually, we displayed the finger’s positions and stimulus deformations in a noisy or precise quality or in a precise quality enhanced by visual force information from color changes of the finger nail. We assessed the reliabilities of the judgments using the method of constant stimuli. In bisensory conditions, discrepancies between the two senses’ information were used to measure each sense’s weight. The reliability of visual judgments was lower with noisy as compared to precise position information, visual force information did not affect reliability. The reliability of bisensory judgments was suboptimal and visual weights were higher than optimal. Not as expected, the visual weights shifted with the visual reliability. The results confirm that visuo-haptic integration of softness information is suboptimal and biased towards vision, but with weights that are “lazy” rather than sticky.
KeywordsSoftness Multisensory Visuo-haptic Psychophysics
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