An examination of Figure 2B, however, shows that the ROC points varied across a comparable range in the patients and controls, suggesting that the response criteria did not different substantially across the groups. More importantly, an advantage of ROC analysis is that differences in response criteria affect only the criteria parameters and not estimates of state- and strength-based perception. So even if there

were differences in response criteria between groups, it would not be expected to affect estimates of perceptual sensitivity. Finally, group differences in response criteria could not explain the results of the MAPK inhibitor fMRI experiment (Experiment 2), in which no patients were examined. Because the hippocampus was the only structure that was damaged in all the patients, these data suggest that the hippocampus itself plays a necessary and selective role in scene perception based on the strength of relational match. Conversely, perceptual judgments based on discrete states find more of identifying specific, local differences in scenes do not seem to depend

on the hippocampus or the MTL. We next conducted an fMRI study with healthy individuals to provide a second test of the hypothesis that the hippocampus is involved in strength-based, but not state-based, perception. The paradigm was similar to that used in Experiment 1 (Figure S1A), with two differences. First, we used sequential rather than simultaneous stimulus presentations, to reduce excessive eye movements that may impact the BOLD response (Kimmig et al., 2001). Second, the confidence scale was changed through in order to enable us to directly assess the role of the hippocampus in state- versus strength-based perception. Rather than the highest-confidence “different” responses being “sure different,” as in the patient study, the highest-confidence “different” responses in the fMRI study were reserved for trials in which individuals experienced a state of being consciously aware of specific details that were different between the images and could, if asked, report those differences. In our

previous work (Aly and Yonelinas, 2012), when individuals made these “perceive different” responses, they were highly accurate at reporting the specific details that had changed. In this way, we could directly examine how the hippocampus is modulated by varying levels of strength-based perception (response confidence “1” to “5”), as compared to the discrete state of identifying specific details (perceive different, “6” responses). Behavioral data are shown in Figures S1B and S1C. The pattern of results was consistent with previous studies (Aly and Yonelinas, 2012) and the patient study, with performance based on a combination of strength- and state-based perception. To identify MTL subregions that contributed to change detection judgments on scenes in this task, we first tested for regions that showed greater activity for correct “different” trials (i.e.