Increases in parieto-occipital alpha-band power reflect involuntary spatial attention due to a task-distracting deviant sound

Imagine you are focusing on the traffic of a busy city street to ride the bike safely. Suddenly, the siren of an ambulance rings out. This unpredictable sound can involuntarily capture your attention and compromise performance. Related to that the present study addresses two questions: 1) Does a shift of spatial attention contribute to this type of distraction? And 2) does oscillatory alpha activity reflect involuntary spatial attention? We harnessed a crossmodal paradigm where participants responded as fast and as correct as possible whether a visual target appeared on the left or right. Each target was preceded by a task-irrelevant sound, usually the same (i.e. standard) animal sound. Rarely, it was a novel (i.e. deviant) environmental sound. Crucially, 50% of the deviants occurred at the same and the other 50% at the opposite side as the target. As expected, responses were slower to targets that followed a task-distracting deviant vs. standard. Crucially, responses were faster when targets followed deviants at the same vs. different side, suggesting a spatial shift of attention. Corroborating support comes from our magnetoencephalographic data. Left-hemispheric visual alpha power increased in response to the left deviant, indicating that visual areas processing information outside the locus of involuntary attention are disengaged. Upon the occurrence of the right deviant right-hemispheric alpha power increased in regions functionally linked to auditory processing and attentional reorienting. Overall, our findings strengthen the view that alpha power indicates an involuntary shift of spatial attention. They further suggest that involuntary attention has a similar impact on target processing as voluntary attention, thus, challenging previous reports claiming otherwise.