UC Irvine

Listeners have a remarkable ability to perceptually segregate interleaved sequences of sounds in complex auditory environments, a process referred to as stream segregation. Previous studies of psychophysical measures of this process in humans and the cat animal model have shown that physical separation of sound sources aids in the process of segregating competing noises. This finding has also been observed in the physiological response of the anesthetized cat primary auditory cortex, wherein neurons tend to synchronize to one of two competing sound sequences differing in their source location. The goal of this dissertation is to evaluate the coding properties of the awake cat auditory cortex and explore the neural mechanisms underlying stream segregation using spatial cues. The cat animal model has been used extensively in auditory research due to their well-developed auditory cortex, and their sound localization abilities to support nocturnal hunting behavior. Here, we trained cats on a psychophysical spatial stream segregation task (Chapter 1). Then, we implanted cats with chronic neural electrodes to record single- and multi-unit activity in the primary auditory cortex. We studied spectral and temporal coding properties of primary auditory cortical neurons in awake cats (Chapter 2), and spatial stream segregation in the response of cortical neurons in off-task conditions (Chapter 3). Our findings show that 1) cats can segregate competing interleaved noise bursts with spatial acuity matching prior measurements in feline and human listeners. 2) Neurons in the primary auditory cortex of awake cats display sharp frequency tuning, temporally dynamic responses, and synchronous and non-synchronized coding of stimuli with high repetition rates—properties that have only previously been observed in the awake marmoset cortex. 3) Neurons in the auditory cortex of cats not overtly engaged in a stream segregation task show weaker segregation than is observed in anesthetized preparations. It may be that presenting stimuli with faster rates, or other mechanisms such as selective attention, are necessary to observe stream segregation in the awake cortex. Further, it may be possible that spatial stream segregation is processed in cortical areas beyond A1. Overall, these findings provide insight into the coding properties of the auditory cortex in awake cats and the neural mechanisms underlying stream segregation using spatial cues.