Combined auditory and visual stimuli facilitate head saccades in the barn owl (Tyto alba)

The barn owl naturally responds to an auditory or visual stimulus in its environment with a quick head turn toward the source. We measured these head saccades evoked by auditory, visual, and simultaneous, co-localized audiovisual stimuli to quantify multisensory interactions in the barn owl. Stimulus levels ranged from near to well above saccadic threshold. In accordance with previous human psychophysical findings, the owl's saccade reaction times (SRTs) and errors to unisensory stimuli were inversely related to stimulus strength. Auditory saccades characteristically had shorter reaction times but were less accurate than visual saccades. Audiovisual trials, over a large range of tested stimulus combinations, had auditory-like SRTs and visual-like errors, suggesting that barn owls are able to use both auditory and visual cues to produce saccades with the shortest possible SRT and greatest accuracy. These results support a model of sensory integration in which the faster modality initiates the saccade and the slower modality remains available to refine saccade trajectory.