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Michael Landy, Stephanie Badde; Feeling a flash. Journal of Vision 2018;18(10):96. doi: https://doi.org/10.1167/18.10.96.
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© ARVO (1962-2015); The Authors (2016-present)
Often, vision provides a more precise location estimate than touch. Consequently, the perceived location of a tactile stimulus is pulled entirely towards the location of a spatially discrepant, synchronously presented, visual stimulus. However, this is only true if the visual and tactile stimuli are perceived as coming from the same source. When perceived from different sources, the perceived tactile location should be unbiased. This leads to a tactile posterior distribution peaking at two separated locations when the same-source judgment is ambiguous. Here, we investigated an observation that participants sometimes report two tactile stimuli in such situations. Participants placed their non-dominant arm parallel to their torso on a tabletop. Tactile stimulators and LEDs were attached to the participant's lower arm (three locations, separated by 3 cm). The arm was occluded from vision by a translucent cover. In each trial, participants received either one or two tactile stimuli with equal probability. In half of the trials, one LED was flashed at the same time as the tactile stimulation. This flash occurred randomly at any one of the three locations. At this range of distances between flash and touch, same-source judgments are ambiguous. Participants reported whether they perceived one or two tactile stimuli, ignoring any visual stimulation. The probability of reporting two tactile stimuli was higher in bimodal trials. Crucially, the probability of erroneously reporting a second illusory tactile stimulus increased with the distance between flash and touch. The probability of correctly reporting two tactile stimuli was higher when the two tactile stimuli had greater spatial separation. A flash increased the probability of correctly reporting two tactile stimuli, especially if the flash was presented at the same location as one of the tactile stimuli. The brain resolves ambiguous spatial information for two tactile locations by perceiving an additional illusory touch.
Meeting abstract presented at VSS 2018
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