Dissociation of Memorability and Memory Encoding in the Brain.

Some images, upon first glance, are more easily remembered than others. Such memorability is highly consistent across people, and thus can be used as an image property for exploring the interaction of perception and memory. We conducted two fMRI experiments to investigate perception of memorable versus forgettable faces and scenes (controlled for possible confounds, including color, spatial frequency, emotion, attractiveness, objects). In Experiment 1 (N=16), participants viewed these images in a block design, while in Experiment 2 (N=16), another participant group viewed these images in an event-related design. Every image was completely novel and presented only once. In both experiments, participants performed an orthogonal image categorization task (i.e., male/female; indoor/outdoor), and were unaware of the experiments' memory-related nature. After scanning, the participants then completed an unexpected memory test. Visual perceptual regions of interest (e.g., fusiform face area, parahippocampal place area) were defined using independent functional localizers, while memory-related regions (medial temporal lobe, MTL) and attention-related regions (intraparietal sulcus, IPS; dorsolateral prefrontal cortex, DLPFC) were anatomically defined. In both experiments, we found significantly greater activation for the memorable than forgettable images in the visual perceptual regions and several MTL regions (perirhinal cortex, PRC; parahippocampal cortex, PHC; amygdala; anterior hippocampus). Further, this memorability effect was found regardless of whether the image was later remembered or forgotten, indicating a dissociation of memorability and subsequent memory. No memorability effect was found in early visual cortex, IPS, or DLPFC, indicating that this effect is not due to visual or attentional confounds. An additional multivariate analysis revealed significantly higher classification for memorable versus forgettable images in PRC. By contrast, activity for memory encoding (remembered versus forgotten images in the subsequent memory task) was only present in the PHC. These results indicate that image memorability may be a dissociable phenomenon from memory encoding, particularly within the PRC. Meeting abstract presented at VSS 2015.