Humans and other animals can attend to one of multiple sounds and follow it selectively over time. The neural underpinnings of this perceptual feat remain mysterious. Some studies have concluded that sounds are heard as separate streams when they activate well-separated populations of central auditory neurons, and that this process is largely pre-attentive. Here, we argue instead that stream formation depends primarily on temporal coherence between responses that encode various features of a sound source. Furthermore, we postulate that only when attention is directed towards a particular feature (e.g. pitch) do all other temporally coherent features of that source (e.g. timbre and location) become bound together as a stream that is segregated from the incoherent features of other sources.
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