Event-related potential N270, a negative component to identification of conflicting information following memory retrieval

Objective: N270, an endogenous ERP component of conflict effect, was evoked in previous studies with S1–S2 paradigm. The present experiment is designed to confirm the speculation that this conflict-related negativity could also be elicited by stimulus probes having conflict with a memorized item in a visual post-retrieval comparison task. Methods: A Sternberg probe-matching paradigm was modified in the present study. The stimuli consisted of a memory set of 3 different items (simple figures) and a retrieval set of 3 probe figures. Subjects matched each probe to its corresponding item in the memory set. The tasks were designed with different conflict loads of no-conflict, low-conflict and high-conflict in the probe retrieval test. Results: Probes of no-conflict elicited a major positive going component, P300, with bilateral parietal distribution. Probes of low- and high-conflict evoked N270, while N430 was elicited only in high-conflict condition. N270 was more negative in high-conflict condition than in low-conflict condition. The N270 was right hemispheric prominent in the low-conflict task and remarkably distributed over the right prefrontal areas. On the other hand, both N270 and N430 were distributed bilaterally on the scalp in the high-conflict task. Conclusions: The present results demonstrate that the N270 is an index to the conflict identification, while the N430 of the high-conflict task reflects the processing for complex conflicts following probe retrieval. These negativities are related to the processing of conflicts