Perceptual restoration of masked speech in human cortex.

Matthew K Leonard,Maxime O Baud,Edward F Chang,Matthias J Sjerps

doi:10.1038/ncomms13619

Abstract

Humans are adept at understanding speech despite the fact that our natural listening environment is often filled with interference. An example of this capacity is phoneme restoration, in which part of a word is completely replaced by noise, yet listeners report hearing the whole word. The neurological basis for this unconscious fill-in phenomenon is unknown, despite being a fundamental characteristic of human hearing. Here, using direct cortical recordings in humans, we demonstrate that missing speech is restored at the acoustic-phonetic level in bilateral auditory cortex, in real-time. This restoration is preceded by specific neural activity patterns in a separate language area, left frontal cortex, which predicts the word that participants later report hearing. These results demonstrate that during speech perception, missing acoustic content is synthesized online from the integration of incoming sensory cues and the internal neural dynamics that bias word-level expectation and prediction.

Highlights

Humans are adept at understanding speech despite the fact that our natural listening environment is often filled with interference
As in natural listening conditions, many factors can influence whether a listener will experience perceptual restoration, and it is even more difficult to know a priori whether a particular stimulus will be perceived in a bistable manner on separate trials
An electrode over left non-primary auditory cortex (STG; Fig. 1e; Supplementary Fig. 1) showed a larger high-gamma response to /s/ compared with /k/ beginning B100 ms after the onset of the critical phoneme

Summary

Introduction

Humans are adept at understanding speech despite the fact that our natural listening environment is often filled with interference. Using direct cortical recordings in humans, we demonstrate that missing speech is restored at the acoustic-phonetic level in bilateral auditory cortex, in real-time This restoration is preceded by specific neural activity patterns in a separate language area, left frontal cortex, which predicts the word that participants later report hearing. Direct neural recordings possess excellent spatial and temporal resolution with a high signal-to-noise ratio, allowing the detection of speech signals at the level of individual phonetic features[7] These properties offer a powerful method to address the cortical representation of subjective perception on a single-trial basis[8]. We asked whether the speech auditory cortex generates representations of the missing phonemes in real time

Methods

Results

Conclusion