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Abstract:
Combining information across different sensory modalities can greatly facilitate our ability to detect or recognize sensory stimuli. Recent work demonstrates that sensory integration is a distributed process, commencing in lower sensory areas and continuing in higher association cortices. Here we investigate the impact that visual stimuli have on the representation of sounds in auditory cortex. To this end we analyze neural responses to naturalistic audio-visual stimuli recorded while monkeys perform a visual fixation task. To characterize multisensory influences we quantify stimulus information provided by different putative neural codes. In particular, we have previously shown (Kayser et al. Neuron 09) that neural activity in auditory cortex is stimulus related on multiple temporal scales, including slow modulation of firing rates, millisecond precise temporal spike patterns and the relative timing of spiking activity to slow (<10Hz) ongoing network activity (phase-of-firing). In the context of multisensory stimuli, we find (Kayser et al. Curr Biol. In Press) that visual stimulation renders spiking responses more reliable across trials (repeats of the same stimulus), and more reliable in time (temporal precision of spikes). This increased reliability enhances the stimulus information provided by neural activity on slow (firing rate) and fast (spike patterns) time scales. As shown by feature extraction, this information gain pertains mostly to temporal sound properties, such as sound envelope, and is much reduced when incongruent visual and auditory stimuli are presented. Overall, these results demonstrate that multisensory influences enhance sensory representations already at early stages in cortex, and do so by enhancing the reliability of stimulus representations on multiple time scales.
