title: Hierarchical neurocomputations underlying concurrent sound segregation: connecting periphery to percept.
abstract: Natural soundscapes often contain multiple sound sources at any given time. Numerous studies have reported that in human observers, the perception and identification of concurrent sounds is paralleled by specific changes in cortical event-related potentials (ERPs). Although these studies provide a window into the cerebral mechanisms governing sound segregation, little is known about the subcortical neural architecture and hierarchy of neurocomputations that lead to this robust perceptual process. Using computational modeling, scalp-recorded brainstem/cortical ERPs, and human psychophysics, we demonstrate that a primary cue for sound segregation, i.e., harmonicity, is encoded at the auditory nerve level within tens of milliseconds after the onset of sound and is maintained, largely untransformed, in phase-locked activity of the rostral brainstem. As then indexed by auditory cortical responses, (in)harmonicity is coded in the signature and magnitude of the cortical object-related negativity (ORN) response (150-200 ms). The salience of the resulting percept is then captured in a discrete, categorical-like coding scheme by a late negativity response (N5; ~500 ms latency), just prior to the elicitation of a behavioral judgment. Subcortical activity correlated with cortical evoked responses such that weaker phase-locked brainstem responses (lower neural harmonicity) generated larger ORN amplitude, reflecting the cortical registration of multiple sound objects. Studying multiple brain indices simultaneously helps illuminate the mechanisms and time-course of neural processing underlying concurrent sound segregation and may lead to further development and refinement of physiologically driven models of auditory scene analysis.
authors.affiliation: Institute for Intelligent Systems, University of Memphis, Memphis, TN, USA; School of Communication Sciences & Disorders, University of Memphis, 807 Jefferson Avenue, Memphis, TN 38105, USA. Electronic address: g.bidelman@memphis.edu.
authors.forename: Gavin M
authors.initials: GM
authors.lastname: Bidelman
authors.affiliation: Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, ON, Canada; Department of Psychology, University of Toronto, Toronto, ON, Canada; Institute of Medical Sciences, University of Toronto, ON, Canada.
authors.forename: Claude
authors.initials: C
authors.lastname: Alain
mesh_terms: D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D001933:Brain Stem / Q000502:physiology*; D003056:Cochlear Nerve / Q000502:physiology*; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D013997:Time Factors; D055815:Young Adult
keywords: Auditory scene analysis; Event-related potentials (ERPs); Frequency-following response (FFR); Object-related negativity (ORN); Reaction time; Sensory systems; Sound classification; Streaming