Bao Hong^1,2 (), Jing Chen², Li Li^1,2; ¹East China Normal University, Shanghai, China, ²New York University Shanghai

Serial dependence is a phenomenon where perception is biased toward recent experience. While this effect is well documented behaviorally, its neural processes remain unclear. To investigate this, we combined eye-tracking and EEG recordings while participants tracked the step-ramp motion of a moving target with its motion direction randomized on each trial. Behavioral analysis revealed robust serial dependence: pursuit directions at initiation were systematically biased toward previous-trial target motion direction, followed by a later repulsive adaptation effect. This dynamic pattern suggests that serial dependence in ocular tracking arises at early stages of visual processing. To uncover its neural basis, we conducted time-resolved multivariate pattern analysis (MVPA) on the EEG signals. While current-trial motion direction could be decoded from EEG signals, previous-trial motion direction also showed a higher-than-chance decoding accuracy, emerging around ~100 ms after stimulus onset and strongest for occipital-parietal electrodes. This suggests that perceptual history might be reactivated within visual cortex early in processing. We next analyzed EEG activity during both stimulus presentation and the inter-trial interval (ITI) using a time-resolved regression with motion direction as the predictor. During stimulus presentation, the regression weights increased sharply after stimulus onset and decreased at the end of trials. During the ITI, the weights showed a gradual rise and exhibited rhythmic fluctuations. Spectral analysis confirmed a significant alpha-band component peaked ~10.5Hz, strongest for occipital-parietal electrodes. Sliding-window analysis revealed increasing alpha amplitude during the ITI, suggesting that past motion information might be retained through rhythmic activity. Together, these findings provide converging behavioral and neural evidence that serial dependence in ocular tracking arises early in visual processing. The retaining of information from previous trials might be linked to rhythmic alpha-band activity in the visual cortex. These results offer insight into how the brain dynamically preserves and reactivates recent motion history to guide ongoing perceptual responses.