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Russell Epstein, Mary Smith, Emily Ward; What is the function of the parahippocampal place area? Testing the context hypothesis. Journal of Vision 2009;9(8):963. doi: 10.1167/9.8.963.
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The parahippocampal place area (PPA) is a region in the human collateral sulcus that responds more strongly to visual scenes (e.g. images of landscapes or cityscapes) than to other visual stimuli. Several competing hypotheses have been offered to explain the response properties of this region. Epstein and Kanwisher (1998) proposed that the PPA encodes spatial layout information, which is obtainable from visual scenes but not from nonscene objects. In contrast, Bar and colleagues propose that the PPA encodes “context” which they define as information about which objects “typically cooccur in the environment around us” (Bar et al., 2008). Evidence for the context hypothesis comes from reports that the PPA responds more strongly to “strong-context” than to “weak-context” objects (Bar & Aminoff, 2003; Bar et al., 2008) and more strongly to famous faces (for which contextual associations are available) than to nonfamous faces (Bar et al., 2008). We re-examined these claims by scanning subjects with fMRI while they viewed scenes, strong and weak context objects, scrambled versions of these objects, and famous/nonfamous faces. Contrary to previous reports, we found that the strong[[gt]]weak context effect was only reliable at slow presentation rates that facilitated mental imagery, while the famous[[gt]]nonfamous face effect did not replicate. Based on these results, we hypothesize that previously reported context effects in the PPA might be explained in part by scene imagery. Rather than being “unequivocal” (Bar et al., 2008), we suggest that the evidence in favor of the context hypothesis is in fact less than compelling, and that the spatial layout account of PPA function is still quite viable.
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