Tactile rivalry demonstrated with ambiguous apparent motion quartet

When observers view ambiguous visual stimuli, their perception will often alternate between the possible interpretations, a phenomenon termed " perceptual rivalry " [1]. To induce perceptual rivalry in the tactile domain, we developed a new tactile illusion, based on the visual apparent motion " quartet " [2]. Pairs of 200 ms vibrotactile stimuli were applied to the finger pad at intervals separated by 300 ms. The location of each successive stimulus pair alternated between the opposing diagonal corners of the ~1 cm 2 stimulation array. This stimulation sequence led all participants to report switches between the perception of motion traveling either up/down or left/right across their fingertip. Adaptation to tactile stimulation biased towards one direction caused subsequent ambiguous stimulation to be experienced in the opposing direction. In contrast, when consecutive trials of ambiguous stimulation were presented, motion was generally perceived in the direction consistent with the motion reported in the previous trial. Voluntary eye movements induced shifts in the tactile perception towards a motion axis aligned along a world-centered coordinate frame. Because the tactile quartet results in switching perceptual states despite unvaried sensory input, it is ideally suited to future studies of the neural processes associated with conscious tactile perception. Rivalry in tactile apparent motion In vision, the apparent motion quartet stimulus consists of pairs of dots alternately presented at the diagonal corners of an invisible square (Figure 1A) [2]. When viewing this stimulus, the dots will appear to switch between jumping either vertically or horizontally between the four corner locations (Figure 1B). To deliver an analogous sequence of vibrotactile pulses to the pad of the right index finger, we used the STReSS 2 tactile stimulator [3] consisting of a grid of piezoelectric tactors (Figure 1C and D). During stimulation with the " tactile quartet " , participants were instructed to continuously report their perceptual experience by holding down one of two keys, corresponding to perceived motion along either the vertical or horizontal axis, respectively. Any time the tactile percept could not be categorized as either vertical or horizontal, participants were told to hold down both keys. Within the first 2 min trial, all 8 subjects reported perceptual switches between vertical and horizontal motion (inter-switch interval: μ = 31.9 s, σ = 14.6 s). While this timing was slower than the 1-10 s switch interval generally reported for other forms of perceptual rivalry [4-6], it was comparable to the rate …