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Robert Volcic, Nadeen Alalami; The role of proprioception in visuo-haptic size perception. Journal of Vision 2017;17(10):360. doi: https://doi.org/10.1167/17.10.360.
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© ARVO (1962-2015); The Authors (2016-present)
Constancy in visual size perception is generally incomplete: the perceived size is affected by changes in fixation distance. Whether haptic and visuo-haptic size perception is subject to the same lack of constancy is, however, as yet unknown. In principle, haptic size perception should not be affected by changes in hand position and should thus be unbiased. But, if so, which sense dominates visuo-haptic size perception? Here we show that visuo-haptic size perception is more than the simple combination of visually and haptically sensed dimensions. Specifically, in Experiment 1, we asked participants to judge the size of two objects placed at different egocentric distances in visual, haptic and visuo-haptic conditions. The point of subjective equality and the discrimination threshold, determined with an adaptive staircase procedure, were taken as a measure of size constancy and precision, respectively. We found a lack of size constancy in both visual and haptic conditions but, surprisingly, not in the visuo-haptic condition. Precision was lowest in the haptic condition with no advantage of the visuo-haptic condition over the visual condition. In Experiment 2, we tested two possibilities that may explain these results. The first was that participants might have estimated the size of objects by comparing them to their own visible hand. The second was that they might have scaled retinal size by the haptically sensed distance. To contrast these two possibilities, we manipulated whether participants could see their hand while grasping objects in the visuo-haptic condition. We found that participants' size constancy and precision were not impacted by the availability of hand vision. In sum, our findings show that imperfect size constancy is found also in haptics, and suggest that visuo-haptic size perception comprises the proprioceptive information about the hand position which promotes visual processing of object's properties.
Meeting abstract presented at VSS 2017
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