Other theoretical frameworks stress the role of the hippocampus in spatial processing in general (Burgess et al., 2002 and O’Keefe and Nadel, 1978), a role that could be extended to perceptual judgments on scenes. LY294002 nmr It has also been argued that the hippocampus is necessary in perceptual tasks that

require binding of information (Warren et al., 2012). These ideas have been challenged by studies failing to find scene perception impairments in patients with hippocampal damage (Hartley et al., 2007, Kim et al., 2011 and Shrager et al., 2006). The current study suggests that the distinction between state- and strength- based perception can help to reconcile the conflict in the literature. In previous studies (Aly and Yonelinas, 2012), we found strong evidence that strength-based perception is affected by manipulations of global featural relationships, whereas state-based perception is disproportionately driven by detection of relatively local, item-level differences. For example, when the only difference between a pair of scenes was a specific feature (e.g., a window in one scene that is absent in the other), perceptual

decisions were based primarily on state-based perception. In contrast, when the featural relations within the scenes differed from one another, performance relied more heavily on strength-based perception. Moreover, individuals reported identifying specific, local details when responses were state-based, and generalized feelings of overall difference/sameness when responses were strength based. In the current fMRI study, the hippocampus

and parahippocampal cortex see more were sensitive to strength-based perception, but, importantly, we also found that other regions of the brain were sensitive to state-based perception. For example, the posterior parietal cortex exhibited state-based, but not strength-based, effects (M.A., C.R., and A.P.Y., unpublished data). Viewed in the context of our previous studies, the present results suggest significant constraints on when and how the hippocampus would be expected to contribute to perception. We propose that the hippocampus is involved in perceptual discriminations that require a representation Oxymatrine of relational or conjunctive information. Not only did the hippocampus track the perceived “strength” of perceptual change, the more basic finding of hippocampal adaptation (greater activation for “different” than “same” trials) suggests the hippocampus forms precise representations of visual scenes. The differences we introduced were subtle—on a given trial, the paired scenes are essentially identical with very small distortions. Thus, finding hippocampal adaptation for such small visual differences provides further evidence that the hippocampus represents precise relational information (Bakker et al., 2008 and Lacy et al., 2011). Because state-based perception plays a larger role in performance when perceptual manipulations involve discrete features (e.g.