Interaction of Streaming and Attention in Human Auditory Cortex

PLOS ONE, Dec 2019

Serially presented tones are sometimes segregated into two perceptually distinct streams. An ongoing debate is whether this basic streaming phenomenon reflects automatic processes or requires attention focused to the stimuli. Here, we examined the influence of focused attention on streaming-related activity in human auditory cortex using magnetoencephalography (MEG). Listeners were presented with a dichotic paradigm in which left-ear stimuli consisted of canonical streaming stimuli (ABA_ or ABAA) and right-ear stimuli consisted of a classical oddball paradigm. In phase one, listeners were instructed to attend the right-ear oddball sequence and detect rare deviants. In phase two, they were instructed to attend the left ear streaming stimulus and report whether they heard one or two streams. The frequency difference (ΔF) of the sequences was set such that the smallest and largest ΔF conditions generally induced one- and two-stream percepts, respectively. Two intermediate ΔF conditions were chosen to elicit bistable percepts (i.e., either one or two streams). Attention enhanced the peak-to-peak amplitude of the P1-N1 complex, but only for ambiguous ΔF conditions, consistent with the notion that automatic mechanisms for streaming tightly interact with attention and that the latter is of particular importance for ambiguous sound sequences.

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Interaction of Streaming and Attention in Human Auditory Cortex

March Interaction of Streaming and Attention in Human Auditory Cortex Alexander Gutschalk 0 1 Andr Rupp 0 1 Andrew R. Dykstra 0 1 0 Department of Neurology, Ruprecht-Karls-Universitat Heidelberg , Heidelberg , Germany 1 Academic Editor: Christian Friedrich Altmann, Kyoto University , JAPAN Serially presented tones are sometimes segregated into two perceptually distinct streams. An ongoing debate is whether this basic streaming phenomenon reflects automatic processes or requires attention focused to the stimuli. Here, we examined the influence of focused attention on streaming-related activity in human auditory cortex using magnetoencephalography (MEG). Listeners were presented with a dichotic paradigm in which left-ear stimuli consisted of canonical streaming stimuli (ABA_ or ABAA) and right-ear stimuli consisted of a classical oddball paradigm. In phase one, listeners were instructed to attend the right-ear oddball sequence and detect rare deviants. In phase two, they were instructed to attend the left ear streaming stimulus and report whether they heard one or two streams. The frequency difference (F) of the sequences was set such that the smallest and largest F conditions generally induced one- and two-stream percepts, respectively. Two intermediate F conditions were chosen to elicit bistable percepts (i.e., either one or two streams). Attention enhanced the peak-to-peak amplitude of the P1-N1 complex, but only for ambiguous F conditions, consistent with the notion that automatic mechanisms for streaming tightly interact with attention and that the latter is of particular importance for ambiguous sound sequences. - Competing Interests: The authors have declared that no competing interests exist. A major challenge for our central auditory system is to segregate simultaneous streams of auditory information that we receive from two or more sound sources. Sequence parameters which determine whether sequentially presented tones are grouped into the same stream have been explored with the so-called streaming paradigm (aka stream segregation) [1]. This paradigm typically uses sequential tone patterns of two or more different tones (e.g., A and B). A number of physical parameters influence whether a sequence is perceived as one integrated stream of alternating tones or as two segregated monotone sequences (e.g. inter-tone interval [2], frequency separation, or F [3,4], and several others [5]). An ongoing debate in the field is the extent to which focused attention influences the streaming process. Bregman [1] suggested that primitive streaming cuessuch as Fcould promote streaming at an early processing stage without requiring attention or other top-down mechanisms. This hypothesis is supported by EEG studies which found that the occurrence of the mismatch negativity (MMN), a component of the auditory evoked response elicited by a change in an otherwise regular stimulus sequence [6], depends on the organization of auditory streams [7,8]. Moreover, the transient waves P1m and N1m evoked by each tone of a sequence increase in amplitude with frequency separation [9,10], probably as a consequence of selective adaptation [11]. This F dependent modulation of the P1m and N1m covaries with listeners rating of streaming perception. All of these evoked response componentsthe P1m, N1m, and MMNcan be recorded while listeners are not engaged in the auditory stimulation and even when attention is focused on another task. However, Carlyon et al. [12] challenged Bregmans view and argued that streaming requires focused attention towards the source to be segregated. These authors used dichotic stimuli and instructed listeners to first listen to their right ear and perform an unrelated distractor task while an ABA_ streaming sequence played in the left ear. Listeners were further instructed to switch their attention to the left ear after the cessation of the distracting task and report their streaming percept of the ABA_ triplets. The results showed that streaming was not stable at the time of the attention switch, but rather required a new build-up period [13,14]. When listeners rated streaming from the beginning of the sequence, in contrast, streaming was at a constantly high level after identical time delays. Moreover, patients with neglect after righthemisphere brain lesions, who have an attentional deficit for left-sided stimuli, showed lower streaming rates for the left-sided sequences [12]. It is well known that focusing attention to one of two sound streams enhances the N1 evoked by each tone of that stream, but typically the stimuli in these experiments were chosen such that the two streams could be readily segregated [15,16,17,18]. The influence of intentional listening on streaming has been known since at least the mid 70s: van Noorden [4] showed that the streaming threshold depends on listeners' attentional set within a range of F and repetition rates. At the lower (upper) F border lies the fission (temporal coh (...truncated)


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Alexander Gutschalk, André Rupp, Andrew R. Dykstra. Interaction of Streaming and Attention in Human Auditory Cortex, PLOS ONE, 2015, 3, DOI: 10.1371/journal.pone.0118962