Vision and audition perform complementary roles in our perception of the environment. In healthy adults, vision provides an accurate and precise reference by which auditory space can be adaptively adjusted to accomplish distinct goals. The goal of this dissertation was to quantify the behavioral processes that underlie audio-visual (AV) spatial perception. </br> There are two ways vision modifies auditory spatial perception. The first resolves disparities between paired AV targets. When there is a mismatch in location between auditory and visual targets, vision tends to “capture” auditory perception, biasing the auditory percept toward its visual counterpart. In an experimental environment the spatial limits of visual capture are tested by introducing disparities between auditory and visual targets and measuring the resultant percept. Visual capture was assessed by having subjects either make forced-choice judgments of whether auditory and visual targets emanate from the same location, or localize the auditory target. Results demonstrated that the spatial boundaries of visual capture are sensitive to task objective, and therefore, these methods of assessing visual capture are not equivalent. </br> A second form of AV interaction maintains spatial congruence across the senses. Prolonged exposure to a fixed spatial AV disparity produces recalibration of auditory space to align it with visual perception. Recent results have implied that this effect also occurs after exposure to a single AV disparity, but the relationship between these results remains unclear. Here, experiments demonstrate two superimposed processes: 1) a rapid effect that acts immediately following visual capture but decays within seconds, 2) a slow recalibration that accumulates over thousands of repetitions of a fixed spatial AV disparity. Visual capture was further demonstrated to have distinct properties when localizing the auditory component of an AV disparity when compared to localizing auditory targets presented following an AV disparity. These results demonstrate that visual capture and recalibration act simultaneously but over different time scales to influence auditory spatial perception. </br> Results from these experiments characterize the distinct behavioral processes that alter auditory spatial perception in response to spatial AV disparities. Understanding these behaviors guides investigation into their physiological roots, and the effects of sensory dysfunction on multisensory perception.

Previous experiments have attempted to measure smooth pursuit eye movements (SPEM) to acoustic targets with limited success. Some studies found no evidence for SPEM (Gauthier and Hofferer, 1967; Schaefer et al., 1981; Boucher et al., 2004; Berryhill et al., 2006) and other studies found only a sub-set of subjects could produce SPEM, which was poor in quality (Krukowski et al., 2001; Hashiba et al., 1996; Cloninger et al., 2013, 2014). These findings are despite evidence of auditory motion perception and an auditory motion aftereffect in the psychoacoustic literature (Carlile and Best, 2002; Dong et al., 2000). This thesis explored a multi-modal question, whether sounds can facilitate or interfere with pursuit of a visual target by moving congruent with or incongruent with linear visual motion, and did so using high-fidelity eye tracking that allowed for examination of the main pursuit characteristics: latency, open-loop acceleration, open-loop peak acceleration, steady-state gain (i.e., eye velocity/ target velocity), and number of “catch-up” saccades. Results showed evidence of facilitation in some characteristics (open-loop peak acceleration) but no evidence of interference, possibly due to the strength of the visual stimulus. Advisors/Committee Members: Watamaniuk, Scott (Advisor).