Event-related potentials evoked by multi-feature conflict under different attentive conditions.

Event-related potentials (ERPs) were recorded in subjects while they were performing a matching task. The focus of the present study was on the contributions made by ERP recording to revealing the time-course of multi-conflict information processing in the brain during visual attention. Participants were instructed to discriminate whether the attributes of the first stimulus (S1) were the same as those of the second one (S2) of a pair. Stimuli were defined by three features: color, global shape, and local shape. In condition 1, all attributes of the two stimuli of the pair were constant (no conflict); in condition 2, S2 was different from S1 in all attributes (conflict). The experiment comprised three tasks. In task 1, subjects attended to the color of the stimuli and ignored the other attributes. In task 2, they were asked to attend to both color and global shape of stimuli and disregard the local shape. In task 3, all attributes were attended to. An ERP component N270 was elicited by attending to the color conflict in session one. In task 2, attending to color and global shape induced two ERP effects in the conflict condition: N270 and N400. The results suggest that the attended different conflicts of the two visual attributes of the stimuli were processed in series. However, in task 3, only one apparent negative component, N270, was observed in the conflict condition. The difference between data from task 2 and 3 showed that more than one processing model exists in the human brain for processing multiple visual attribute conflicts.