Involuntary orienting of attention to sight or sound relies on similar neural biasing mechanisms in early visual processing.

A sudden visual or acoustic change in the environment can capture attention involuntarily and facilitate perceptual processing of a subsequent visual target at the same location. The behavioral consequences of this involuntary (exogenous) cueing of attention have been well documented, but the underlying neural mechanisms and how they may differ depending on the modality of the cue remain unknown. We here report the effects of a spatially uninformative visual cue on the processing of a subsequent visual target and neural activity elicited by the cue itself and compare these results to the effects of an auditory cue. The results reveal that both visual and auditory cues enhanced the perceived brightness contrast of the subsequent co-localized target and boosted early cortical processing of the target beginning at about 100 ms post-target onset. Furthermore, both visual and auditory cues elicited a slow positive deflection (visible on target-absent trials) that was larger over contralateral relative to ipsilateral occipital scalp regions and was hypothesized to reflect the biasing of visual sensitivity for potential targets at that location. Overall, the data suggest that sudden events in the environment - regardless of sensory modality - initiate involuntary shifts of attention to the event's location and that the visual-perceptual consequences and neural mechanisms of these involuntary shifts are qualitatively similar for auditory and visual events.