One of the most significant and poorly understood aspects of auditory function is the ability to listen selectively to one of the many acoustic signals normally present in the environment. At any moment attention can be focused on a given sound, such as when listening to the violoncello among the other instruments in a string quarter, or to sounds originating from a specific spatial location, such as when eavesdropping on a conversation taking place at a neighboring table at a restaurant. Without changing the position of the receptors, i.e., moving the head, attention can be shifted to different acoustic signals, or to different acoustic sources, establishing in this manner the difference between hearing and listening. This phenomenon has been referred to as the cocktail party problem, the solution of which is constantly used in social and non-social situations by many species. Thus, the question arises of how the nervous system shifts attention. Psychological theories of attention have proposed two different types of explanations for this phenomenon: "late selection" mechanisms that create biases at the decision-making level, or "early selection" mechanisms that modulate the processing of sensory information to facilitate the detection of stimuli in selected areas of space. The available evidence from behavioral studies of humans, as well as physiological evidence from the visual cortex of behaving primates, supports the notion of "early selection". Dr. Populin will test the hypothesis that facilitation of auditory spatial behavior by covert attention is mediated by early selection mechanisms resulting from descending signals that modulate sensory processing at the highest levels of the auditory hierarchy (auditory cortex). The experiments will be carried out with behaving, head-unrestrained monkeys in a protocol recently developed by Dr. Populin to study spatial auditory function. First, the research will document the effects of attention on spatial auditory behavior. Specifically, it will investigate the effects of auditory attention on detection and localization of acoustic signals in the free field with both single and multiple sources (Specific Aim 1). Second, he will investigate the effect of spatial attention on the response properties of single neurons in auditory cortex (Specific Aim 2). Little is known about the neural mechanisms underlying auditory attention, in particular in comparison to visual attention. The results of the present project are expected to begin fill such a void. The broader impacts of Dr. Populin's are strong. He regularly involves undergraduate students, especially women, in his research program and participates in much outreach about science to inner city youth, often giving talks in Spanish to ESL audiences. Furthermore, he shares his data on a website so that other scientists and school groups may work with them for scientific and training purposes.
