Abstract
BackgroundHumans are able to extract regularities from complex auditory scenes in order to form perceptually meaningful elements. It has been shown previously that this process depends critically on both the temporal integration of the sensory input over time and the degree of frequency separation between concurrent sound sources. Our goal was to examine the relationship between these two aspects by means of magnetoencephalography (MEG). To achieve this aim, we combined time-frequency analysis on a sensor space level with source analysis. Our paradigm consisted of asymmetric ABA-tone triplets wherein the B-tones were presented temporally closer to the first A-tones, providing different tempi within the same sequence. Participants attended to the slowest B-rhythm whilst the frequency separation between tones was manipulated (0-, 2-, 4- and 10-semitones).ResultsThe results revealed that the asymmetric ABA-triplets spontaneously elicited periodic-sustained responses corresponding to the temporal distribution of the A-B and B-A tone intervals in all conditions. Moreover, when attending to the B-tones, the neural representations of the A- and B-streams were both detectable in the scenarios which allow perceptual streaming (2-, 4- and 10-semitones). Alongside this, the steady-state responses tuned to the presentation of the B-tones enhanced significantly with increase of the frequency separation between tones. However, the strength of the B-tones related steady-state responses dominated the strength of the A-tones responses in the 10-semitones condition. Conversely, the representation of the A-tones dominated the B-tones in the cases of 2- and 4-semitones conditions, in which a greater effort was required for completing the task. Additionally, the P1 evoked fields’ component following the B-tones increased in magnitude with the increase of inter-tonal frequency difference.ConclusionsThe enhancement of the evoked fields in the source space, along with the B-tones related activity of the time-frequency results, likely reflect the selective enhancement of the attended B-stream. The results also suggested a dissimilar efficiency of the temporal integration of separate streams depending on the degree of frequency separation between the sounds. Overall, the present findings suggest that the neural effects of auditory streaming could be directly captured in the time-frequency spectrum at the sensor-space level.
Highlights
Humans are able to extract regularities from complex auditory scenes in order to form perceptually meaningful elements
By varying the inter-tonal frequency separations, we expected to access integrated versus segregated percepts in the time-frequency spectrum
The present findings are consistent with previous studies suggesting that the perceptual organization in sequential auditory scene analysis relies on oscillatory entrainment to task-driven sound input
Summary
Humans are able to extract regularities from complex auditory scenes in order to form perceptually meaningful elements. The vast majority of researchers interpret the streaming effect in terms of tonotopic organization of the auditory system [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] According to this interpretation, frequency-distant sounds are processed into distinct neural populations and heard as separate streams, and frequency adjacent sounds are processed in neighboring neural channels leading to their perceptual integration into one unified auditory object. The formation of different auditory streams requires temporal integration of sound input over time [20,21]
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