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Performance on tests of source memory is typically based on recollection of contextual information associated with an item. However, recent neuroimaging results have suggested that the perirhinal cortex, a region thought to support familiarity-based item recognition, may support source attributions if source information is encoded as a feature of the relevant item (i.e. “unitized”). We hypothesized that familiarity may contribute to source memory performance if item and source information are unitized during encoding, whereas performance may rely more heavily on recollection if source information is encoded as an arbitrary contextual association. Three source recognition experiments examining receiver operating characteristics (ROCs) and response deadline performance, indicated that familiarity makes a greater contribution to source memory if source and item information are unitized during encoding. These findings suggest that familiarity can contribute to source recognition, and that its contribution depends critically on the way item and source information are initially processed.

The medial temporal lobes (MTL) are critical for episodic memory but the functions of MTL subregions are controversial. According to memory strength theory, MTL subregions collectively support declarative memory in a graded manner. In contrast, other theories assert that MTL subregions support functionally distinct processes. For instance, one view is that perirhinal cortex (PRc) processes item information, parahippocampal cortex (PHc) processes context information, and the hippocampus binds item and context. Here, we report two experiments that tested competing predictions from these models. In these studies, subjects encoded color-word associations by imagining color either as a contextual association (context detail condition) or as a feature of the item to be encoded (item detail condition). Results showed that encoding color information as an item detail improved source recognition in amnesic patients with recollection deficits. Furthermore, eventrelated fMRI data from healthy subjects revealed PRc activation associated with successful retrieval of item details, whereas activation in the hippocampus and PHc was associated with recollectionbased source retrieval. The qualitatively different patterns of results observed in PRc and hippocampus/PHc are inconsistent with a memory strength account and are consistent with the idea that different MTL regions process different types of episodic information. Keywords memory; hippocampus; parahippocampal; memory formation; medial; temporal The medial temporal lobes (MTL) are critical for episodic memory, but the specific functions of MTL subregions, such as the hippocampus, perirhinal cortex (PRc), and parahippocampal cortex (PHc), are controversial. Some dual process theories propose a fundamental difference between these regions, such that the hippocampus is necessary for recollection of context information or relational memory, whereas the surrounding cortex is critical for familiaritybased item memory (Brown & Aggleton, 2001; N. J. Cohen & Eichenbaum, 1993;Yonelinas, 2002). Consistent with this view, functional magnetic resonance imaging (fMRI) studies have shown that hippocampal activity is correlated with successful performance on source memory tests, thought to depend on recollection, whereas PRc activity is correlated with item familiarity (e.g. Davachi, Mitchell, & Wagner, 2003;Kensinger & Schacter, 2006;Ranganath et al., 2003;Tendolkar et al., 2008;Weis et al., 2004). An alternative memory strength-based account of this dissociation is that, due to nonlinearities in the BOLD signal in fMRI studies, hippocampal activation is sensitive to gradations in high but not low strength memories, Corresponding Author: Rachel A. Diana, radiana@ucdavis.edu, NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscriptwhereas PRc activation is sensitive to gradations in low but not high strength memories (Squire, Wixted, & Clark, 2007). Importantly, however, recent neuroimaging results have found that patterns of PHc activity in recognition memory exp...

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