These findings, taken together, implicate the perirhinal cortex i

These findings, taken together, implicate the perirhinal cortex in processing of high ambiguity objects in this perceptual task. They form a baseline for the use of this paradigm in probing perceptual abilities of individuals with amnesia. Six amnesic patients were tested in this same-different discrimination task, four with damage limited to the hippocampus and two with more extensive lesions of the MTL, including http://www.selleckchem.com/products/gsk2656157.html the perirhinal cortex. The extent of brain

damage in these patients has been extensively characterized to exclude possible alternative explanations of their deficits. The amnesic patients with MTL damage, but not those with restricted hippocampal damage, were impaired in the high ambiguity object discriminations,

but not in low ambiguity object discriminations or size discriminations (whether easy or hard). These observations are consistent with perceptual deficits in patients with amnesia following MTL damage and focus attention on the perirhinal cortex as the critical locus for these deficits when considered alongside the fMRI study in control subjects. It is important to emphasize that the perceptual deficits in these patients are not general in nature. These individuals are perfectly capable of making same-different judgments on the same kinds of objects, as long as they do not have Wnt inhibitor many overlapping features. The representational-hierarchical view predicts perceptual deficits following perirhinal cortex damage only when feature ambiguity is high, which is precisely what is observed in this study (as well as in other studies that have identified perceptual deficits in patients with MTL damage, e.g., Barense et al., 2005 and Lee et al., 2005). Thus, MTL structures are important for perception, even though patients with MTL amnesia do not have global visual agnosia. Patients

demonstrate preserved performance on difficult perceptual tasks that do not specifically tax the resolution of feature ambiguity (see Baxter, 2009). In fact, it below turns out that the patients with MTL amnesia can make same-different perceptual judgments even for high ambiguity objects, under a particular set of circumstances. Barense et al. (2012) noted that the performance of their MTL amnesics on high ambiguity discriminations was normal during the beginning of the block, but then deteriorated dramatically. This is not a fatigue effect, because it is not present in the equally challenging difficult size discriminations. They hypothesized, based on the representational-hierarchical model, that the perceptual failure in their MTL amnesics was due to the accumulation of interfering visual information at earlier levels of the ventral visual stream.

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