Evidence for Neural Computations of Temporal Coherence in an Auditory Scene and Their Enhancement during Active Listening

TLDR

The brain segregates overlapping sounds by exploiting temporal coherence of neural populations, a mechanism supported by psychoacoustic and fMRI studies using stochastic figure‑ground stimuli. This study extends those findings by using high‑resolution EEG to probe how temporal coherence is computed in the brain. Subjects were presented with stochastic figure‑ground stimuli whose figure coherence varied over time, and linear regression was applied to EEG data under active and passive listening to isolate the neural signature of temporal‑coherence processing. Passive listening elicited a 115–185 ms coherence response, while active listening amplified and prolonged this effect to ~265 ms, demonstrating early, preattentive temporal‑coherence computations enhanced by active analysis.

Abstract

The human brain has evolved to operate effectively in highly complex acoustic environments, segregating multiple sound sources into perceptually distinct auditory objects. A recent theory seeks to explain this ability by arguing that stream segregation occurs primarily due to the temporal coherence of the neural populations that encode the various features of an individual acoustic source. This theory has received support from both psychoacoustic and functional magnetic resonance imaging (fMRI) studies that use stimuli which model complex acoustic environments. Termed stochastic figure-ground (SFG) stimuli, they are composed of a "figure" and background that overlap in spectrotemporal space, such that the only way to segregate the figure is by computing the coherence of its frequency components over time. Here, we extend these psychoacoustic and fMRI findings by using the greater temporal resolution of electroencephalography to investigate the neural computation of temporal coherence. We present subjects with modified SFG stimuli wherein the temporal coherence of the figure is modulated stochastically over time, which allows us to use linear regression methods to extract a signature of the neural processing of this temporal coherence. We do this under both active and passive listening conditions. Our findings show an early effect of coherence during passive listening, lasting from ∼115 to 185 ms post-stimulus. When subjects are actively listening to the stimuli, these responses are larger and last longer, up to ∼265 ms. These findings provide evidence for early and preattentive neural computations of temporal coherence that are enhanced by active analysis of an auditory scene.