Contribution of the parietal cortex to auditory-stream perception

University Of Pennsylvania, Philadelphia PA

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Abstract

SUMMARY A primary goal of the auditory system is to transform acoustic stimuli arriving at the ear into distinct perceptual representations (i.e., sounds or auditory streams). Traditionally, auditory perception is associated with the hierarchical computations that occur along the ?ventral? auditory pathway. However, several lines of evidence indicate that the ?dorsal? auditory pathway (i.e., the intraparietal area [area LIP])?which is traditionally associated with sound localization and audiomotor processing?may also contribute to auditory- stream perception. In particular, it is thought that the dorsal pathway contributes to the processes that allow an auditory stream to be segregated from a background environment (i.e., auditory scene analysis, including figure-background segregation). This grant proposal tests the contribution of area LIP to auditory-stream perception by evaluating the neural principles that underlie auditory-stream perception in the dorsal auditory pathway. To achieve this goal, we test the contribution of neural activity in macaque lateral intraparietal area (area LIP) to auditory perception while monkeys participate in an objective test of auditory streaming (i.e., the ?streaming? task). This single-interval two-alternative forced-choice task requires a monkey to report whether a ?test? stimulus is to the left or to the right of a ?reference? stimulus, while in the presence of a ?masker? stimulus. By titrating the temporal coherence between the reference/test and the masker stimuli, the reference/test stimuli become grouped or segregated from the masker stimulus. That is, they become single or distinct auditory streams. This manipulation also makes the task more or less difficult. In Aim #1, we identify the contribution of neural activity in macaque lateral intraparietal area (area LIP) to auditory-stream perception. The contribution of spiking activity in the dorsal pathway to auditory-stream perception is not fully understand. To gain insight into these neural mechanisms, rhesus monkeys participate in the detect-target task. We record single-neuron LIP spiking activity while monkeys perform the streaming task. We test two hypotheses. Specifically, we hypothesize that (1) monkeys will perform better when the test stimulus is presented incoherently from the masker stimulus (i.e., when they segregate into different streams) than when they are presented coherently (i.e., grouped into one stream) and (2) LIP sensitivity will reflect the degree to which the test and masker stimuli form separate streams and will correlate with behavioral performance.