Cortical Processing of Binaural Cues as Shown by EEG Responses to Random-Chord Stereograms

Henri Pöntynen,Nelli Salminen

doi:10.1007/s10162-021-00820-4

Abstract

Spatial hearing facilitates the perceptual organization of complex soundscapes into accurate mental representations of sound sources in the environment. Yet, the role of binaural cues in auditory scene analysis (ASA) has received relatively little attention in recent neuroscientific studies employing novel, spectro-temporally complex stimuli. This may be because a stimulation paradigm that provides binaurally derived grouping cues of sufficient spectro-temporal complexity has not yet been established for neuroscientific ASA experiments. Random-chord stereograms (RCS) are a class of auditory stimuli that exploit spectro-temporal variations in the interaural envelope correlation of noise-like sounds with interaurally coherent fine structure; they evoke salient auditory percepts that emerge only under binaural listening. Here, our aim was to assess the usability of the RCS paradigm for indexing binaural processing in the human brain. To this end, we recorded EEG responses to RCS stimuli from 12 normal-hearing subjects. The stimuli consisted of an initial 3-s noise segment with interaurally uncorrelated envelopes, followed by another 3-s segment, where envelope correlation was modulated periodically according to the RCS paradigm. Modulations were applied either across the entire stimulus bandwidth (wideband stimuli) or in temporally shifting frequency bands (ripple stimulus). Event-related potentials and inter-trial phase coherence analyses of the EEG responses showed that the introduction of the 3- or 5-Hz wideband modulations produced a prominent change-onset complex and ongoing synchronized responses to the RCS modulations. In contrast, the ripple stimulus elicited a change-onset response but no response to ongoing RCS modulation. Frequency-domain analyses revealed increased spectral power at the fundamental frequency and the first harmonic of wideband RCS modulations. RCS stimulation yields robust EEG measures of binaurally driven auditory reorganization and has potential to provide a flexible stimulation paradigm suitable for isolating binaural effects in ASA experiments.

Highlights

The auditory system faces the ill-posed scene analysis problem of having to separate sound mixtures arriving at the ears into behaviorally useful information about the identities and locations of sound sources in the environment (Bregman 1994)
The responses consist of five distinct regions: 1) the large deflection at the stimulus onset (0 - 1 s), 2) the steady-state response during the noise segment where the interaural envelope correlation is zero, 3) a change-onset response around 3 s, where the Random-chord stereograms (RCS) modulations begin, 4) the steady-state response
The grandaverage event-related potentials (ERP) show that the time course of wideband RCS modulations is reflected in the time-domain representation of the ERPs

Summary

Introduction

The auditory system faces the ill-posed scene analysis problem of having to separate sound mixtures arriving at the ears into behaviorally useful information about the identities and locations of sound sources in the environment (Bregman 1994). The apparent ease with which the sense of hearing accomplishes this task implies that systematic computational principles facilitate the process. Many salient scene analysis cues are accessible monaurally (Bregman 1994; Darwin 1997; Grimault et al 2002; Moore and Gockel 2002; Carlyon 2004; Alain 2007; Snyder and Alain 2007; Shamma and Micheyl 2010; Moore and Gockel 2012; Simon 2015), and evidence for auditory perceptual organization has been found already in the cochlear nucleus (Pressnitzer et al 2008). Binaural hearing facilitates scene analysis and yields. Salminen: Cortical Processing of Binaural Cues as Shown by EEG Responses to

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