Abstract
What makes an image memorable? People encounter hundreds of images throughout their days, in real-life situations, on billboards, or on their computers or cell phones. Yet, people do not remember all images equally well. Some images are intrinsically more memorable than others (Bainbridge, Isola, & Oliva, 2013; Isola, Xiao, Parikh, Torralba, & Oliva, 2014; Khosla, Xiao, Torralba, & Oliva, 2012). While image memorability (typically measured as hit rate) is only weakly affected by low-level image properties, such as color, saturation, or spatial frequencies, high-level properties, such as semantics, emotion, popularity, or aesthetics, were shown to have stronger relationships with memorability. Here we investigate the influence on memorability exerted by mid-level perceptual grouping features, such as contour curvature, contour junctions, or local symmetry. To this end, we converted scene images from the FIGRIM Dataset (Bylinskii et al., 2015) into line drawings and computed their mid-level features. Our results suggest a positive relationship between local mirror symmetry and hit rate for the old/new memory task. Interestingly, we also found a positive correlation between local mirror symmetry and false alarm rate. Following re-analysis of the data using signal detection theory, we found no connection between any of the mid-level features and d-prime. In spite of that, we found a strong positive relationship between local mirror symmetry and the decision criterion, indicating that participants were more likely to respond that they had seen the image before, irrespective of whether the image had been seen before or not. We hypothesize that local symmetry improves perceptual fluency by reducing the complexity of features in the image, thereby leading to an enhanced feeling of familiarity, which may lead to a decision bias toward reporting having seen the image before. However, symmetry did not affect the sensitivity of the memory recognition task.