Neuronal Substrates of Perceptual Salience in the Auditory System

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You are standing in the midst of a departmental social event with a plastic cup of wine in your hand, idly thinking about your cat, while the sound of multiple ongoing conversations washes over you. Suddenly, you hear your name mentioned in one of those conversations, and what was formerly an indistinct hum of voices separates into background noise and a foreground conversation that now commands your full attention. How does this happen? How is perceptual salience represented in the auditory brain? How does auditory processing interact with behavioural state and attention to differentiate hearing from listening?We have recently developed powerful new computational tools for addressing these questions, which have enabled us to analyse how the context in which a sound occurs affects the representation of that sound in the auditory brain. Using these novel tools, we have found that context-sensitive mechanisms in the auditory system implement, at a single-neuron level, well-known perceptual phenomena that describe how humans parse complex sounds into salient events. Therefore, these context-sensitive mechanisms may be the neuronal substrates of perceptual salience in the auditory system. We hypothesise that changes in these context-sensitive mechanisms underlie changes in perceptual salience during active listening - for example, when you suddenly realize that one individual voice in multiple ongoing conversations is talking about you.We will test this hypothesis by recording the responses of auditory cortical, thalamic and midbrain neurons to complex sounds while animals are attending to auditory or visual cues in two different behavioral tasks. By comparing the context-dependence of neurons between brain areas, sensory attentional states, and behavioural tasks, we aim to determine how perceptual salience arises from interactions between attention and neuronal sensitivity to sound context. Ultimately, this work may not only reveal the neuronal substrates of perceptual salience in the auditory system, but also suggest new approaches to unsolved problems in machine listening -- such as how to extract the sound of an individual voice from multiple ongoing conversations.