Distraction by deviant sounds: Response repetition vs. response change.

In oddball paradigms, rare deviant stimuli reliably produce behavioral distraction, disrupting performance in ongoing primary tasks. However, the specific mechanisms through which deviance affects response selection and execution remain unclear. Recent evidence suggests that deviant sounds may differentially affect response repetitions and response changes, but whether these effects reflect a single underlying process or functionally independent mechanisms has not been established. We investigated this question using a cross-modal auditory-visual oddball task in which participants (N = 115) identified visual target locations while ignoring standard (80%) or deviant (20%) tones. Critically, we manipulated response set size between participants (two-alternative forced-choice [2-AFC] vs. four-alternative forced-choice [4-AFC]) while holding deviant probability constant, testing whether deviance effects on repetitions and changes differ in their sensitivity to response uncertainty. Results revealed a clear dissociation: deviant sounds slowed response repetitions in both conditions, demonstrating response-specific inhibition that was insensitive to response uncertainty, but facilitated response changes more strongly in 2-AFC than 4-AFC, demonstrating context-sensitive facilitation that scales inversely with the number of response alternatives. These findings suggest that deviance effects on response repetition and response change may reflect functionally independent mechanisms with different computational properties, and that unexpected events may shape action control through coordinated inhibitory and facilitative processes.