Abstract
Salient unexpected and task-irrelevant sounds can act as distractors by capturing attention away from a task. Consequently, a performance impairment (e.g., prolonged RTs) is typically observed along with a pupil dilation response (PDR) and the P3a ERP component. Previous results showed prolonged RTs in response to task-relevant visual stimuli also following unexpected sound omissions. However, it was unclear whether this was due to the absence of the sound's warning effect or to distraction caused by the violation of a sensory prediction. In our paradigm, participants initiated a trial through a button press that elicited either a regular sound (80%), a deviant sound (10%), or no sound (10%). Thereafter, a digit was presented visually, and the participant had to classify it as even or odd. To dissociate warning and distraction effects, we additionally included a control condition in which a button press never generated a sound, and therefore no sound was expected. Results show that, compared with expected events, unexpected deviants and omissions lead to prolonged RTs (distraction effect), enlarged PDR, and a P3a-like ERP effect. Moreover, sound events, compared with no sound events, yielded faster RTs (warning effect), larger PDR, and increased P3a. Overall, we observed a co-occurrence of warning and distraction effects. This suggests that not only unexpected sounds but also unexpected sound omissions can act as salient distractors. This finding supports theories claiming that involuntary attention is based on prediction violation.