Dataset Information

Temporal coherence in the perceptual organization and cortical representation of auditory scenes.

ABSTRACT: Just as the visual system parses complex scenes into identifiable objects, the auditory system must organize sound elements scattered in frequency and time into coherent "streams." Current neurocomputational theories of auditory streaming rely on tonotopic organization of the auditory system to explain the observation that sequential spectrally distant sound elements tend to form separate perceptual streams. Here, we show that spectral components that are well separated in frequency are no longer heard as separate streams if presented synchronously rather than consecutively. In contrast, responses from neurons in primary auditory cortex of ferrets show that both synchronous and asynchronous tone sequences produce comparably segregated responses along the tonotopic axis. The results argue against tonotopic separation per se as a neural correlate of stream segregation. Instead we propose a computational model of stream segregation that can account for the data by using temporal coherence as the primary criterion for predicting stream formation.

SUBMITTER: Elhilali M

PROVIDER: S-EPMC2673083 | biostudies-literature | 2009 Jan

REPOSITORIES: biostudies-literature

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Temporal coherence in the perceptual organization and cortical representation of auditory scenes.

Elhilali Mounya M Ma Ling L Micheyl Christophe C Oxenham Andrew J AJ Shamma Shihab A SA

Neuron 20090101 2

Just as the visual system parses complex scenes into identifiable objects, the auditory system must organize sound elements scattered in frequency and time into coherent "streams." Current neurocomputational theories of auditory streaming rely on tonotopic organization of the auditory system to explain the observation that sequential spectrally distant sound elements tend to form separate perceptual streams. Here, we show that spectral components that are well separated in frequency are no longe ...[more]

PMID: 19186172

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Project description:This combined fMRI and MEG study investigated brain activations during listening and attending to natural auditory scenes. We first recorded, using in-ear microphones, vocal non-speech sounds, and environmental sounds that were mixed to construct auditory scenes containing two concurrent sound streams. During the brain measurements, subjects attended to one of the streams while spatial acoustic information of the scene was either preserved (stereophonic sounds) or removed (monophonic sounds). Compared to monophonic sounds, stereophonic sounds evoked larger blood-oxygenation-level-dependent (BOLD) fMRI responses in the bilateral posterior superior temporal areas, independent of which stimulus attribute the subject was attending to. This finding is consistent with the functional role of these regions in the (automatic) processing of auditory spatial cues. Additionally, significant differences in the cortical activation patterns depending on the target of attention were observed. Bilateral planum temporale and inferior frontal gyrus were preferentially activated when attending to stereophonic environmental sounds, whereas when subjects attended to stereophonic voice sounds, the BOLD responses were larger at the bilateral middle superior temporal gyrus and sulcus, previously reported to show voice sensitivity. In contrast, the time-resolved MEG responses were stronger for mono- than stereophonic sounds in the bilateral auditory cortices at ~360 ms after the stimulus onset when attending to the voice excerpts within the combined sounds. The observed effects suggest that during the segregation of auditory objects from the auditory background, spatial sound cues together with other relevant temporal and spectral cues are processed in an attention-dependent manner at the cortical locations generally involved in sound recognition. More synchronous neuronal activation during monophonic than stereophonic sound processing, as well as (local) neuronal inhibitory mechanisms in the auditory cortex, may explain the simultaneous increase of BOLD responses and decrease of MEG responses. These findings highlight the complimentary role of electrophysiological and hemodynamic measures in addressing brain processing of complex stimuli.

Project description:In human and animal auditory perception the perceived quality of sound streams changes depending on the duration of inter-sound intervals (ISIs). Here, we studied whether adaptation and the precision of temporal coding in the auditory periphery reproduce general perceptual boundaries in the time domain near 20, 100, and 400 ms ISIs, the physiological origin of which are unknown. In four experiments, we recorded auditory brainstem responses with five wave peaks (P1 -P5) in response to acoustic models of communication calls of house mice, who perceived these calls with the mentioned boundaries. The newly introduced measure of average standard deviations of wave latencies of individual animals indicate the waves' temporal precision (latency jitter) mostly in the range of 30-100 μs, very similar to latency jitter of single neurons. Adaptation effects of response latencies and latency jitter were measured for ISIs of 10-1000 ms. Adaptation decreased with increasing ISI duration following exponential or linear (on a logarithmic scale) functions in the range of up to about 200 ms ISIs. Adaptation effects were specific for each processing level in the auditory system. The perceptual boundaries near 20-30 and 100 ms ISIs were reflected in significant adaptation of latencies together with increases of latency jitter at P2-P5 for ISIs < ~30 ms and at P5 for ISIs < ~100 ms, respectively. Adaptation effects occurred when frequencies in a sound stream were within the same critical band. Ongoing low-frequency components/formants in a sound enhanced (decrease of latencies) coding of high-frequency components/formants when the frequencies concerned different critical bands. The results are discussed in the context of coding multi-harmonic sounds and stop-consonants-vowel pairs in the auditory brainstem. Furthermore, latency data at P1 (cochlea level) offer a reasonable value for the base-to-apex cochlear travel time in the mouse (0.342 ms) that has not been determined experimentally.

Dataset Information

Temporal coherence in the perceptual organization and cortical representation of auditory scenes.

Publications

Temporal coherence in the perceptual organization and cortical representation of auditory scenes.

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