Hierarchical processing underpins competition in tactile perceptual bistability

Abstract

Ambiguous sensory information can lead to spontaneous alternations between perceptual states, recently shown to extend to tactile perception. The authors recently proposed a simplified form of tactile rivalry which evokes two competing percepts for a fixed difference in input amplitudes across antiphase, pulsatile stimulation of the left and right fingers. This study addresses the need for a tactile rivalry model that captures the dynamics of perceptual alternations and that incorporates the structure of the somatosensory system. The model features hierarchical processing with two stages; a first stage resolves perceptual competition, leading to perceptual alternations; and a second stage encodes perceptual interpretations. The first stage could be located downstream of brainstem nuclei and the second stage could be located within the primary somatosensory cortex (area 3b). The model captures dynamical features specific to the tactile rivalry percepts and produces general characteristics of perceptual rivalry: input strength dependence of dominance times (Levelts proposition II), short-tailed skewness of dominance time distributions and the ratio of distribution moments. The presented modelling work leads to experimentally testable predictions. The same hierarchical model could generalise to account for percept formation, competition and alternations for bistable stimuli that involve pulsatile inputs from the visual and auditory domains. Author summaryPerceptual ambiguity involving the touch sensation has seen increased recent interest. It provides interesting opportunity to explore how our perceptual experience is resolved by dynamic computations in the brain. We recently proposed a simple form of tactile rivalry where stimuli consisted of antiphase sequences of high and low intensity pulses delivered to the right and left index fingers. The stimulus can be perceived as either one simultaneous pattern of vibration on both hands, or as a pattern of vibrations that jumps from one hand to the other, giving a sensation of apparent movement. During long presentation of the stimuli, ones perception switches every 5-20 seconds between these two interpretations, a phenomenon called tactile perceptual bistability. This study presents the first computational model for tactile bistability and is based on the structure of sensory brain areas. The model captures important characteristics of perceptual interpretations for tactile rivalry. We offer predictions in terms of how left-right tactile intensity differences are encoded and propose a location for the encoding of perceptual interpretations in sensory brain areas. The model provides a generalisable framework that can make useful predictions for future behavioural experiments with tactile and other types of stimuli.