Tactile rivalry demonstrated with ambiguous apparent motion quartet
Carter, Konkle, Wang, Hayward, & Moore
During sustained viewing of ambiguous visual stimuli, an observer's visual experience will generally switch between each of the possible interpretations, a phenomenon termed perceptual rivalry. To induce perceptual rivalry in the tactile domain, we developed a new tactile illusion, based on the visual apparent motion "quartet" (Ramachandran & Anstis, 1985).
Using the STReSS2 tactile stimulator consisting of a 6x10 array (~1 cm2) of piezoelectric actuators we applied discrete vibrotactile pulses to the pad of the right index finger. Two pulses (100 Hz, 200 ms) were applied to diagonally opposed corners of the stimulation array. At intervals of 300ms, the location of the pulse pair were alternated between the opposing diagonal corners of the stimulation grid. During 2min blocks of this stimulation sequence, participants reported the sensation of motion traveling either up/down or left/right across their fingertip, with the perceived axis of motion spontaneously switching at an average interval of 28.5 sec (+-13.7). This rate of switching was slower than that generally reported for other forms of perceptual rivalry, but was more than twice as fast as that reported by the same subjects for a visual motion quartet with equivalent timing parameters. Prior exposure to 20 sec of biased tactile motion caused subsequent periods of ambiguous stimulation to be perceived in the opposing direction. Voluntary eye-movements, but not mental imagery, significantly increased the number of perceptual switches reported. By systematically comparing the effects of rotating the head or hand 90 degrees, the perceived tactile motion was found to show a strong bias to be consistent with the direction of eye movements in world-centered coordinate space.
This research suggests that, when faced with sensory ambiguity, perceptual rivalry may be a strategy common to all modalities. The fact that the tactile quartet results in changing perceptual states despite unvaried tactile stimulation, makes it ideal for future experiments aimed at identifying the neural processes necessary for conscious tactile perception.
Carter, O. L., Konkle, T., Wang, Q., Hayward, V., & Moore, C. I. Tactile rivalry demonstrated with ambiguous apparent motion quartet. Program No. 178.25. 2008 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2008. Online.