Image Memorability in the Eye of the Beholder: Tracking the Decay of Visual Scene Representations

Some images stick in your mind for days or even years, while others seem to vanish quickly from memory. We tested whether differences in image memorability 1) are already evident immediately after encoding, 2) produce different rates of forgetting, and 3) whether the retrieval of images with different memorability scores affords differential degrees of cognitive load, mirrored by graded pupillary and blink rate responses. We monitored participants’ eye activity while they viewed a sequence of >1200 images in a repetition detection paradigm. 240 target images from 3 non-overlapping memorability classes were repeated at 4 different lags. Overall, performance decreased log-linearly with time. Differences in memorability were already visible at the shortest lag (~ 20 sec) and became more pronounced as time passed on. The rate of forgetting was steepest for low memorable images. We found that pupils dilated significantly more to correctly identified targets than correctly rejected distractors. Importantly, this “pupil old/new effect” increased with increasing number of lags and decreasing image memorability. A similar modulation of blink rates corroborated these findings. These results suggest that during memory retrieval of scenes, image inherent characteristics pose differential degrees of cognitive load on observers as seen in their eyes.