Tracking the mismatch information in visual short term memory: an event-related potential study.

Although the mechanisms of visual short term memory (VSTM) are extensively investigated in the recent decade, how we compare the representation stored in VSTM to the perceptual input to detect and process the mismatch information remains largely unclear. The current study explored whether there is an ERP component tracking the mismatch process in VSTM by adopting a delayed matching task. To exclude non-memory factors, for instance, using perceptual representation which dominated in previous studies using this paradigm, we lengthened the blank interval between the two sequentially displayed stimuli to 4 s to ensure the first stimuli is stored in VSTM. In order to test the sensitivity of this potential neural index and its functional relation to VSTM comparison process, colored shapes were adopted as materials while both the target feature color and the irrelevant feature shape could be changed. We found both the target feature change and the irrelevant feature change elicited a more negative component N270 (or N2-enhancement) around the anterior areas, with their neural sources located at frontal lobe. These results suggest that the N270 can sensitively reflect the mismatch information between the representation in VSTM and the perceptual input. Moreover, it may reflect the limited-capacity process in the VSTM-perception comparison, in which a deliberative comparison was conducted after an unlimited-capacity comparison process.