Audiovisual localization in the Barn Owl (Tyto alba): Stimulus Intensity and Timing Effects

Elizabeth Whitchurch, Institute of Neuroscience, University of Oregon

Abstract
Barn owls use auditory and visual modalities to detect and orient toward potential prey. We measured head saccade reaction times (SRT) and accuracy to auditory, visual and audiovisual stimuli. The relative timing of the unisensory information in the audiovisual response was manipulated by altering the stimulus intensity, and the stimulus onset asynchrony (SOA). In unisensory trials, the SRT and error increased as a function of decreasing intensity. On average, saccades to visual targets were more accurate; whereas those to auditory targets had shorter SRTs. SRTs to simultaneous audiovisual stimuli were as short as the shortest unimodal SRTs, and did not positively violate the race model inequality. Additionally, these multisensory saccades generally had errors as small as the most accurate unimodal trials. Thus, simultaneous audiovisual stimuli often evoked saccades with SRTs as short as the auditory and as accurate as the visual trials. These general trends were maintained as audiovisual SOA were varied. Our results suggest an updating model of audiovisual integration in saccade generation in the owl. This model is tested by measuring single unit multisensory receptive fields as a function of time in the optic tectum.

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