Redundant perceptual inputs modulate early neural activity patterns in visual working memory: Evidence from EEG decoding

Repeated information in visual input can improve behavioral performance in visual working memory (VWM) under capacity limitations. However, it remains unclear whether neural activity scales with the amount of perceptual redundancy in the same way as behavioral performance. Such activity may vary gradually with perceptual redundancy, or it may follow a pattern in which fully redundant arrays elicit neural activity patterns distinct from those elicited by arrays containing any orientation differences. Conventional behavioral measures and univariate event-related potentials (ERPs) cannot fully distinguish these possibilities, motivating the present study to apply multivariate pattern analysis (MVPA) to a published EEG dataset. In a VWM change-detection task, participants remembered visual arrays containing all-same, partial-different, or all-different orientation bars. Time-resolved decoding revealed early neural differentiation, around 200 ms after stimulus onset, between the all-same condition and the other two conditions, indicating that condition-related neural activity patterns diverged during encoding. Cross-temporal decoding showed limited generalization from encoding to maintenance, suggesting that condition-related neural patterns changed over time rather than being expressed as a single stable code. In contrast to whole-scalp decoding, decoding based on contra-vs-ipsi difference signals revealed condition-related differentiation primarily during later maintenance (around 780 ms after stimulus onset), closely resembling the temporal profile of prior CDA findings. Cross-condition decoding further showed that partial-different trials were classified as more similar to all-different arrays than to all-same arrays. Together, these findings suggest that neural activity associated with perceptual redundancy in VWM is more consistent with a separation-based account: visual arrays with fully identical items elicit an early neural activity pattern distinct from the patterns elicited by arrays containing any orientation differences, whereas partial redundancy preserves a pattern closer to that of fully distinct arrays.