Primitive Auditory Stream Segregation: A Neurophysiological Study in the Songbird Forebrain

Abstract

Auditory stream segregation refers to the perceptual grouping of sounds, to form coherent representations of objects in the acoustic scene, and is a fundamental aspect of hearing and speech perception. The perceptual segregation of simple interleaved tone sequences has been studied in humans and European starlings (Sturnus vulgaris) using sequences of 2 alternating tones differing in frequency (ABA-ABA-ABA-...). The segregation of A and B tones into separate auditory streams is believed to be promoted by preattentive auditory processes that increase the separation of excitation patterns along a tonotopic gradient. We tested the hypothesis that frequency selectivity and forward masking operate as 2 preattentive processes in sequential stream segregation by recording neural responses in the auditory forebrain of awake starlings to repeated ABA- sequences in which we varied the frequency separation (DeltaF) between the A and B tones and the tone repetition time (TRT). The A tones were presented at the neurons' characteristic frequency (CF), and B tones differed from the CF over a one-octave range. Larger DeltaF values and shorter TRTs promote the perceptual segregation of alternating tone sequences in humans and also resulted in larger differences in neural responses to alternating CF (A) and non-CF (B) tones. Our results are consistent with the hypothesis that preattentive auditory processes, such as frequency selectivity and forward masking, contribute to the perceptual segregation of sequential acoustic events having different frequencies into separate auditory streams, but also suggest that additional processes may be required to account for all known perceptual effects related to sequential auditory stream segregation.

Neuromagnetic Correlates of Streaming in Human Auditory Cortex

“…When they presented alternating tone sequences (ABAB) to awake macaques and recorded at the A-tone best-frequency site in A1, the B tones were suppressed at smaller ⌬F as the ISI between tones decreased (Fishman et al, 2004). Similar findings have been obtained in bats (Kanwal et al, 2003) and birds (Bee and Klump, 2004). It is unclear, however, how these data relate to the P 1 m and N 1 m data in our study.…”

Neural processing of natural sounds

“…Similarly, responses in human auditory cortex use a gain control to emphasize the temporal modulations characteristic of speech. Neurophysiological studies in primates [130,131] and birds [132] have also begun to unravel how multiple auditory streams could be represented in the auditory system. In summary, auditory neuroscientists have mostly focused their attention to understanding the computations needed to passively recognize and categorize natural sounds and much more research is needed to understand how acoustical signals are processed in active communications and in natural soundscapes.…”

Multistability in auditory stream segregation: a predictive coding view

“…In this case, links between same-feature events are established first, because the reduction of link strength between adjacent sounds owing to high feature separation (e.g. by topological distance in a tonotopically organized area of the auditory cortex; [60,61]) exceeds that caused by longer temporal separation between the non-adjacent (but same feature) sounds. In other words, the cost of establishing the link between topologically highly separate focuses of neural activity exceeds that of establishing the link between the neural activity elicited by the incoming sound and a relatively more decayed neural after-effect of the previous (less recent) same-feature sound.…”