Investigating the Neural Correlates of a Streaming Percept in an Informational-Masking Paradigm

Abstract

Humans routinely segregate a complex acoustic scene into different auditory streams, through the extraction of bottom-up perceptual cues and the use of top-down selective attention. To determine the neural mechanisms underlying this process, neural responses obtained through magnetoencephalography (MEG) were correlated with behavioral performance in the context of an informational masking paradigm. In half the trials, subjects were asked to detect frequency deviants in a target stream, consisting of a rhythmic tone sequence, embedded in a separate masker stream composed of a random cloud of tones. In the other half of the trials, subjects were exposed to identical stimuli but asked to perform a different task—to detect tone-length changes in the random cloud of tones. In order to verify that the normalized neural response to the target sequence served as an indicator of streaming, we correlated neural responses with behavioral performance under a variety of stimulus parameters (target tone rate, target tone frequency, and the “protection zone”, that is, the spectral area with no tones around the target frequency) and attentional states (changing task objective while maintaining the same stimuli). In all conditions that facilitated target/masker streaming behaviorally, MEG normalized neural responses also changed in a manner consistent with the behavior. Thus, attending to the target stream caused a significant increase in power and phase coherence of the responses in recording channels correlated with an increase in the behavioral performance of the listeners. Normalized neural target responses also increased as the protection zone widened and as the frequency of the target tones increased. Finally, when the target sequence rate increased, the buildup of the normalized neural responses was significantly faster, mirroring the accelerated buildup of the streaming percepts. Our data thus support close links between the perceptual and neural consequences of the auditory stream segregation.

Sound segregation via embedded repetition is robust to inattention.

“…Another more recently studied streaming paradigm consists of a repeated target tone stream in a background of desynchronized tone pips of varying frequency (exhibiting “informational masking,” or IM; Akram, Englitz, Elhilali, Simon, & Shamma, 2014 ; Elhilali, Xiang, Shamma, & Simon, 2009 ; Gutschalk, Micheyl, & Oxenham, 2008 ; Kidd, Mason, Deliwla, Woods, & Colburn, 1994 ). Brain responses that correlate with IM target-stream awareness are abolished when attention is diverted away from the IM stimulus, a finding taken to indicate that segregation is reliant on attention (e.g., Gutschalk et al, 2008 ).…”

Large-Scale Analysis of Auditory Segregation Behavior Crowdsourced via a Smartphone App

“…Previous laboratory-based research on auditory scene analysis employed synthetic stimuli that are conventionally based on simple signals such as pure tones, sequences of tones of different frequencies, or speech-in-noise for instance [ 8 , 9 , 10 ]. We designed a stimulus that consists of a series of chords containing random frequencies that change from one chord to another.…”

Auditory Figure-Ground Segregation is Impaired by High Visual Load

“…Evidence of segregation in the supposed absence of directed attention (e.g. 30, 42, 47 ) has been taken to indicate that segregation takes place automatically and pre-attentively, and that attention operates at a subsequent stage to enhance the representation of attended objects and suppress distracters 20, 49–52 , for example by modulating the temporal coherence of neural populations 3 . Specifically in the context of SFG segregation, accumulating work in humans has shown ‘figure’-evoked brain responses in naïve, distracted listeners, suggesting an early pre-attentive computation of temporal coherence 24–26 that is enhanced during active listening 24 .…”