Abstract
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.
Highlights
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
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
Even when attention is distracted, the response is significantly stronger for large ΔF associated with two-streams percepts than for small ΔF associated with one-stream percepts
Summary
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). An ongoing debate in the field is the extent to which focused attention influences the streaming process. Bregman [1] suggested that primitive streaming cues—such as ΔF—could promote streaming at an early processing stage without requiring attention or other top-down
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