Neural Correlates of Auditory Perceptual Awareness and Release from Informational Masking Recorded Directly from Human Cortex: A Case Study.

Andrew R Dykstra,Alexander Gutschalk,Emad N Eskandar,Sydney S Cash,Eric Halgren

doi:10.3389/fnins.2016.00472

Abstract

In complex acoustic environments, even salient supra-threshold sounds sometimes go unperceived, a phenomenon known as informational masking. The neural basis of informational masking (and its release) has not been well-characterized, particularly outside auditory cortex. We combined electrocorticography in a neurosurgical patient undergoing invasive epilepsy monitoring with trial-by-trial perceptual reports of isochronous target-tone streams embedded in random multi-tone maskers. Awareness of such masker-embedded target streams was associated with a focal negativity between 100 and 200 ms and high-gamma activity (HGA) between 50 and 250 ms (both in auditory cortex on the posterolateral superior temporal gyrus) as well as a broad P3b-like potential (between ~300 and 600 ms) with generators in ventrolateral frontal and lateral temporal cortex. Unperceived target tones elicited drastically reduced versions of such responses, if at all. While it remains unclear whether these responses reflect conscious perception, itself, as opposed to pre- or post-perceptual processing, the results suggest that conscious perception of target sounds in complex listening environments may engage diverse neural mechanisms in distributed brain areas.

Highlights

In complex acoustic environments, perceiving sounds of interest is often limited by informationprocessing bottlenecks in the central auditory system rather than resolution of the auditory periphery, a phenomenon known as informational masking (Pollack, 1975; Kidd et al, 2008)
Intracranial Correlates of Auditory Perceptual Awareness perceptual awareness and release from informational masking, such studies can inform the study of conscious perception across sensory modalities (Cariani and Micheyl, 2012; Snyder et al, 2015), for which there is a paucity of data outside the context of vision (Dehaene and Changeux, 2011; Koch et al, 2016)
The results suggest that detecting sounds of interest in adverse listening situations may engage diverse brain areas, including auditory cortex on the posterior superior temporal gyrus as well as frontal and temporal areas involved in attention and target detection (Halgren, 2008)

Summary

Introduction

In complex acoustic environments, perceiving sounds of interest is often limited by informationprocessing bottlenecks in the central auditory system rather than resolution of the auditory periphery, a phenomenon known as informational masking (Pollack, 1975; Kidd et al, 2008). A commonly-used paradigm to study informational masking involves presenting a target stream of tones amidst a random multi-tone background (Neff and Green, 1987), with target tones surrounded by a protected frequency region (Neff et al, 1993) to prevent energetic masking at the auditory periphery (Delgutte, 1990). Such randomly-varying maskers, combined with uncertainty about the features comprising the target (e.g., if the pitch of the target varies across trials), drastically decrease the probability of target sounds reaching awareness (Kidd et al, 2008). What role other brain areas might play in overcoming informational masking and gating target sounds to awareness remains an open question

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