Auditory P3a reflects attentional process, not response inhibition to deviant processing: an ERP study with three-stimulus oddball paradigm.

In a three-stimulus oddball task, the P3a event-related potential (ERP) is typically elicited by an infrequent deviant, with its amplitude increasing under difficult task conditions. In the visual modality, this P3a enhancement has been shown to reflect attentional process rather than response inhibition to the deviant. This study aimed to examine whether P3a amplitude increase by task difficulty in the auditory modality also reflects attentional process. The same experimental design as in the visual study was applied, manipulating stimulus category (three- vs. two-category) and task difficulty (easy vs. difficult). In the three-category condition, stimuli included standard tones, target deviant tones, and non-target deviant chords, with only target deviant tones requiring a response. In the two-category condition, stimuli were categorized into standard tones, target deviant tones and target deviant chords. Thus, the difference between the two conditions is that deviant chords were non-target or target. Task difficulty was varied by adjusting frequency distance between standard tones and target deviant tones. If P3a reflects attentional process, enhancement should occur in both conditions, while response inhibition would only enhance P3a in the three-category condition. Results showed that P3a amplitude increased by task difficulty occurred in both conditions, supporting the attentional process hypothesis. The fact that the P3a augmentation reflects attentional process regardless of sensory modality suggests that this process is mediated by modality-independent neural mechanisms.