Cognitive Neurosciences and Neuropsychology

A deviant sound in a sequence of repeating (standard) sounds elicits the mismatch negativity (MMN) component in the event-related brain potential (ERP) recorded from the scalp.1 The MMN is elicited even when the subject is instructed to ignore the auditory stimuli and attend to other stimuli. In the ERP to deviant sounds, the MMN overlaps with the negative N1 (peak latency about 100 ms from stimulus onset) and subsequent positive P2 components which are also elicited by standard sounds. The MMN is apparently generated by a neuronal process activated by a mismatch between the afferent neuronal activity caused by a deviant stimulus and an automatically formed memory trace representing physical and temporal features of a repeated standard stimulus. Source modelling has suggested MMN generators bilaterally in the auditory cortex2–5 and an additional source in the frontal lobe.3,5 MMN activity in the auditory cortex, which is also observed in intracranial recordings,6,7 is presumably generated by the neuronal mismatch detection process described above, while the frontal activity might be generated by a frontal process initiating an involuntary switching of attention to a deviant sound.1,3 The subsequent involuntary orienting of attention might, in turn, be reflected by the positive P3a component8 following the MMN9 and elicited with a large amplitude of several microvolts by attention-catching widely deviant sounds, such as a telephone ringing.10–13 The P3a to such novel sounds appears to have sources in multiple brain areas, including the temporal and frontal cortices.7,10–12,14–17 According to recent studies,18,19 even deviant tones differing by < 20% in frequency from standard tones and eliciting only small MMN and P3a responses (1–2 mV at the fronto-central scalp) may cause an involuntary switching of attention. In these studies, a deviant tone preceding an auditory or visual target stimulus prolonged reaction times to targets and increased response errors in relation to targets preceded by a standard tone. However, in both studies, the task-irrelevant standard and deviant tones preceding the target stimuli may have acted as warning stimuli informing about the time of target occurrence. Thus the subjects may have attended to each task-irrelevant tone and the detrimental effects of deviant tones on performance may not indicate involuntary attention to deviant tones, but distraction caused by a change in the attended warning stimuli. The present study examined effects of deviant tones on ERPs and visual task performance in a more controlled condition where a visual warning stimulus was presented simultaneously with each tone in order to keep attention away from the tones. Cognitive Neurosciences and Neuropsychology