Chirag H Deepak¹ (), Joan Danielle K. Ongchoco¹; ¹The University of British Columbia

Visual processing organizes continuous visual input into discrete events. The boundaries between these events facilitate adaptive forgetting: when the statistics of our immediate environments have dramatically changed, it may be helpful to ‘clear’ memory of previous information that no longer applies to the new event. Event boundaries have been explored in many contexts—from scene cuts in film, chapters in narratives, and even walking through doorways. But one of the clearest and most natural event boundaries we cross is simply going from one day to the next. The time of the day can be marked by external clocks and calendars, but it can also be more implicitly extracted from the position of the sun. Here we asked whether these subtler visual cues are spontaneously encoded, and in turn, then trigger active forgetting. Observers watched virtual animations in which they were situated in a waiting room with three windows. They were shown a list of pseudo-words, after which the animation played simulating the actual movement of the sun over the course of the day. The position of the sun was implied only by the shadows reflected by objects in the room. Observers either saw a sunrise-to-noon or noon-to-sunset transition. Animations were matched for duration and visual complexity, differing only in the direction of lighting changes. Recognition memory was tested immediately after. Results revealed worse memory in the noon-to-sunset compared to the sunrise-to-noon condition. No such memory differences were found in a control experiment with matched internal room lighting changes (i.e., brightening versus dimming light strips), with the sun position remaining constant throughout. This confirms that the observed memory effects were driven by sun position rather than general illumination changes. Altogether, these findings suggest that the visual system uses environmental priors, such as the sun’s position, to regulate memory dynamically.