The effects of selective attention on ERPs elicited by visual and auditory deviant stimuli

The effects of deviant visual and auditory stimuli on event-related potentials were investigated in an intermodal oddball task. Tones of different pitch were used as auditory stimuli (standard: 1,000 Hz, 85%, deviant 800 Hz, 15%) and various single Chinese words and simple geometric figures were used as visual stimuli. Auditory and visual stimuli were presented sequentially to subjects at randomized ISI of 700-1,300 ms. The subjects in one block were instructed to attend the visual channel and ignore the auditory and in the other to attend auditory and ignore visual with key-responses to the attended stimuli. Results showed that the deviant auditory stimuli elicited similar mismatch negativity in both attended and unattended conditions. The attended auditory MMN overlapped the N2b and followed by a P3a component that may reflect the orienting response. In the visual modality, the deviant visual stimuli elicited no MMN or MMN-like component in both conditions. The enhanced P300 elicited by the auditory and visual deviant stimuli in active condition. The results were consistent with Naatanen's observation on MMN.