Abstract
Although vision is considered the dominant modality, recent studies demonstrate the influence of other modalities on visual perception (Shams et al. 2000, Sekuler et al., 1999, Ernst et al., 2000). We report an extension of the “sound-induced flash illusion,” (Shams et al., 2000) to the tactile-visual domain, yielding the “touch-induced flash illusion.” Methods: Visual stimulus consisted of a uniform grey disk presented at 7 degree eccentricity below the fixation point for 10 ms. Tactile stimulation was provided by a refreshable Braille cell consisting of a 2×4 array of plastic pins which were raised simultaneously for 34 ms and provided a salient stimulation to the tip of the left index finger. A factorial design was used with two factors: the number of flashes (1 or 2), and number of taps (0, 1, 2). Thirty trials of each condition were presented in random order to nine naïve subjects. The task was to judge the number of flashes seen on the screen. Results: On average, observers reported seeing two flashes on 63% of trials when a single flash was accompanied by two taps, compared to 15% of trials when it was presented in the absence of taps. Furthermore, signal detection theory analysis indicated that double taps caused a change in sensitivity in visual discrimination. This radical change in perception was consistent across all subjects tested. Conclusion: These findings provide further evidence challenging the notion that visual perception is independent of activity in other modalities.