Differences in processing violations of sequential and feature regularities as revealed by visual event-related brain potentials.

Identifying novel or unexpected events which violate predictions based on the regularities extracted from our environment is crucially important for adaptive behavior. However, the exact dynamics of processing such events is not well understood. Furthermore, it is not known in which degree the process of deviant detection differs across contexts and how much it depends on the characteristics of deviant events. This issue was addressed by the present study which used event-related potentials (ERPs) in order to investigate the dynamics of identifying two types of deviants presented within the same visual setting. These events violated expectations based on two different types of information contained within each trial, either temporal order of stimulus presentation (sequential deviant) or physical attributes shared by the majority of individual stimuli (feature deviant). The obtained results indicate a certain degree of similarity in detecting two deviant types which, when task-relevant, both elicited N2 and P3b event-related potential components. However, significant differences across different stages of their processing were also identified. First, only feature, but not sequential deviants elicited an N1 enhancement. Furthermore, N2 and P3b responses elicited by sequential and feature deviants differed in their latency and topography and, in case of P3b, amplitude. Taken together, these results suggest that the dynamics of detecting different types of deviants strongly depends on the specific characteristics of such events. Furthermore, the identified differences in the topography of N2 and P3b indicate distinct mechanisms underlying several stages of their processing.