Stimuli that are unexpected, relatively infrequent, and task-irrelevant can grab attention to the detriment of ongoing tasks. In the surprise-induced blindness (SiB) and surprise-induced deafness (SiD) paradigms, such stimuli render participants unaware of a task-relevant probe presented 300-400 ms thereafter. These initially profound detection deficits, however, quickly habituate across surprise trials. We sought to identify the electroencephalography (EEG) markers of SiB and SiD to better understand the deficits' causes and relationship. Human participants (n = 33; 18 males, 15 females) completed the paradigms in counterbalanced order while EEG was recorded. Participants evidenced SiB and SiD: Probe detection was severely impaired, but only for the first few surprise trials. In contrast, detection was consistently high during standard trials. Surprise-induced deficits were accompanied by a late parietal positivity time-locked to surprise stimulus presentations, which attenuated by trial alongside the behavioral effects. These qualities are characteristic of the P3 complex, especially its novelty P3 (nP3) component, suggesting that SiB and SiD are a consequence of extended stimulus evaluation indexed by the nP3. Putative nP3s were similar for the visual and auditory paradigms, akin to the similar behavioral deficits. Nevertheless, individual differences in behavioral deficit magnitudes were not correlated across modalities, and encountering surprises in one modality did not reduce their effect in the other. Probe-evoked and early perceptual-related components also differed greatly by modality and did not habituate. Our results suggest that surprise-induced deficits are due to late, modality-specific attentional limitations with similar behavioral outcomes and neural features.
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