Thiti Chainiyom¹, Chaipat Chunharas¹; ¹Cognitive Clinical & Computational Neuroscience Lab, Faculty of Medicine, Chulalongkorn University

Are we more likely to notice something that comes back after being gone, or something that slowly slips away? Kind of like a familiar song that briefly disappears from the radio and then returns. This study explores how the timing and frequency of exposure—rather than meaning—shape implicit learning and familiarity. We used basic visual shapes (colored squares or circles) with no emotional or semantic content and showed them in two patterns: first the shape would appear frequently, rarely occur, and then back to frequent again. Then, it would turn into a B shape (reverse pattern). All stimuli were shown the same number of times and were counterbalanced across participants. We created a visual target detection test consisting of 480 trials with 16 participants (n=16). We started with a baseline of 160 trials (equal exposure to A and B), followed by 10 blocks of 32 trials (16 A and 16 B). Over time, we gradually changed how often the A and B stimuli appeared. We looked at performance across two phases (Phase 1: blocks 1–5, Phase 2: blocks 6–10), analyzing both accuracy and response time (RT). Participants responded faster to B stimuli as the task went on, while accuracy was higher for A stimuli, especially during Phase 2. A two-way ANOVA showed a strong interaction between condition and phase (F(1,60) = 32.67, p < .001), along with a main effect of phase (F(1,60) = 8.06, p = 0.006). Although accuracy was high overall, only the A condition showed a clear improvement during Phase 1. Our results suggest that people can pick up on patterns just from when and how often something appears. The A condition felt more familiar when it came back, possibly reflecting memory reactivation.