Nonlinear dynamics in auditory cortical activity reveal the neural basis of perceptual warping in speech categorization

Abstract

Surrounding context influences speech listening, resulting in dynamic shifts to category percepts. To examine its neural basis, event-related potentials (ERPs) were recorded during vowel identification with continua presented in random, forward, and backward orders to induce perceptual nonlinearities. Behaviorally, sequential order shifted listeners categorical boundary vs. random delivery revealing perceptual warping (biasing) of the heard phonetic category dependent on recent stimulus history. ERPs revealed later ([~]300 ms) activity localized to superior temporal and middle/inferior frontal gyri that predicted listeners hysteresis magnitudes. Findings demonstrate that top-down, stimulus history effects on speech categorization are governed by interactions between frontotemporal brain regions.