Abstract
BackgroundThe aim of the present study was to identify a specific neuronal correlate underlying the pre-attentive auditory stream segregation of subsequent sound patterns alternating in spectral or temporal cues. Fifteen participants with normal hearing were presented with series’ of two consecutive ABA auditory tone-triplet sequences, the initial triplets being the Adaptation sequence and the subsequent triplets being the Test sequence. In the first experiment, the frequency separation (delta-f) between A and B tones in the sequences was varied by 2, 4 and 10 semitones. In the second experiment, a constant delta-f of 6 semitones was maintained but the Inter-Stimulus Intervals (ISIs) between A and B tones were varied. Auditory evoked magnetic fields (AEFs) were recorded using magnetoencephalography (MEG). Participants watched a muted video of their choice and ignored the auditory stimuli. In a subsequent behavioral study both MEG experiments were replicated to provide information about the participants’ perceptual state.ResultsMEG measurements showed a significant increase in the amplitude of the B-tone related P1 component of the AEFs as delta-f increased. This effect was seen predominantly in the left hemisphere. A significant increase in the amplitude of the N1 component was only obtained for a Test sequence delta-f of 10 semitones with a prior Adaptation sequence of 2 semitones. This effect was more pronounced in the right hemisphere. The additional behavioral data indicated an increased probability of two-stream perception for delta-f = 4 and delta-f = 10 semitones with a preceding Adaptation sequence of 2 semitones. However, neither the neural activity nor the perception of the successive streaming sequences were modulated when the ISIs were alternated.ConclusionsOur MEG experiment demonstrated differences in the behavior of P1 and N1 components during the automatic segregation of sounds when induced by an initial Adaptation sequence. The P1 component appeared enhanced in all Test-conditions and thus demonstrates the preceding context effect, whereas N1 was specifically modulated only by large delta-f Test sequences induced by a preceding small delta-f Adaptation sequence. These results suggest that P1 and N1 components represent at least partially-different systems that underlie the neural representation of auditory streaming.
Highlights
The aim of the present study was to identify a specific neuronal correlate underlying the preattentive auditory stream segregation of subsequent sound patterns alternating in spectral or temporal cues
The amplitude of the P1 component was generally found to have increased for Δf = 4 semitones compared to Δf = 2 semitones (significant main effect Δf [F(1,14) = 23.468, p < .001]), whereas the amplitude of the N1 component was only slightly stronger in Δf = 4 semitones compared to Δf = 2 semitones
The N1 amplitude was significantly enhanced in both conditions (4 and 2 semitones) in the right hemisphere compare to left hemisphere only on a Test position (interaction Hemisphere x Part for N1 amplitude [F(1,14) = 13.993, p < .05])
Summary
The aim of the present study was to identify a specific neuronal correlate underlying the preattentive auditory stream segregation of subsequent sound patterns alternating in spectral or temporal cues. The frequency separation (delta-f) between A and B tones in the sequences was varied by 2, 4 and 10 semitones. The brain’s ability to constantly organize auditory objects or “auditory streams” from the competing sounds in the environment is a key element in human auditory perception. This phenomenon has been labeled “stream segregation” or “streaming” by Bergman and Campbell [1,2]. When the frequency separation (Δf ) between the tones is small and the inter stimulus interval (ISI) is long, the sequence is typically heard as one sound stream, like a gallop. At intermediate Δf and ISI values, the perception could bias in favor of one stream or two streams, depending on participants’ attention [3,5] and the duration of listening [6]
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