When old information is intermixed with new elements: An event-related potential study

•Mechanisms of old/new effect were induced by intermixed stimuli.•Intermixed stimuli elicited a greater old/new effect.•Intermixed stimuli were categorized as new stimuli.•Cognitive processing of intermixed stimuli is more difficult. Previous research has focused on the event-related potential of the old/new effect, but the mechanism for cognitive conflict and subsequent integration processing both induced by intermixed (old and new) stimuli have not been widely researched. This paper describes the effect of familiar stimuli mixed with new information and presented as intermixed stimuli. Three conditions were set within a study-test paradigm incorporating old, new, and intermixed conditions. The intermixed condition resulted in the lowest accuracy, thereby implying the greatest old/new effect. Moreover, compared with the old condition, the intermixed condition elicited a greater N270 as well as a stronger N400, while the new condition only induced a stronger N270. These results elucidate that when new information is intermixed with old information, the old/new effect is more pronounced, indicating that intermixed stimuli are possibly more difficult to integrate than old and new stimuli.