What we see helps us interpret what we hear. Integrating visual and auditory information is a fundamental aspect of human behavior. Impairments in visual-auditory integration impact numerous aspects of human health, ranging from communication and language to attention and movements in a complicated environment. However, the neural basis of this ability is not well understood. Previous work in barn owls has focused on how the visual information is used to calibrate the representation of auditory space, and has implicated the inferior colliculus in this process. However, little is known about this area in primates. Rhesus monkeys have visual and auditory systems that are quite similar to humans, and serve as an excellent animal model for studying the neural mechanisms underlying visual-auditory integration. Visual-auditory integration in humans and monkeys is different from barn owls because primates can move their eyes whereas barn owls cannot. Thus, primate visual auditory integration requires three signals: visual, auditory, and eye position signals. It has long been known that the primate IC contains auditory information, and we have recently shown that it contains eye position information (Groh et al., Neuron, 2001). Here, we turn to visual information in this structure. We have recently discovered robust visual responses in the IC of awake monkeys. In this proposal, we seek to study the properties of these visual responses and how they relate to auditory and eye position information in this brain region. Specifically, we aim to (1) characterize the visual response properties (Aim 1), (2) determine the frame of reference of these visual responses (Aim 2), and determine how IC neurons respond to combined visual and auditory stimuli, especially when a spatial disparity between these stimuli produces a ventriloquism affect/aftereffect (Aim 3). The mechanisms of visual influence over auditory processing investigated here bear on a variety of disorders involving both visual and auditory components, such as dyslexia and autism. These experiments will yield a greater understanding of subcortical mechanisms for visual-auditory integration within the auditory pathway and may ultimately lead to treatment regimens to help ameliorate the deficits experienced by patients with these disorders.
