The human medial temporal lobe processes online representations of complex objects

Abstract

There has been considerable debate as to whether structures in the medial temporal lobe (MTL) support both memory and perception, in particular whether the perirhinal cortex may be involved in the perceptual discrimination of complex objects with a large number of overlapping features. Similar experiments testing the discrimination of blended images have obtained contradictory findings, and it remains possible that reported deficits in object perception are due to subtle learning in controls, but not patients. To address this issue, a series of trial-unique object "oddity" tasks, in which subjects selected the odd stimulus from a visual array, were administered to amnesic patients with either selective bilateral damage to the hippocampus or more extensive damage to MTL regions, including the perirhinal cortex. Whereas patients with damage limited to the hippocampus performed similarly to controls on all conditions, patients with perirhinal damage were significantly impaired when the task required discrimination between objects with a large number of features in common. By contrast, when the same stimuli could be discriminated using simple visual features, patients with perirhinal damage performed normally. These results are consistent with a theoretical view which holds that rostral inferotemporal cortical regions, including perirhinal cortex, represent the complex conjunctions of stimulus features necessary for both perception and memory of objects.

The perirhinal cortex modulates V2 activity in response to the agreement between part familiarity and configuration familiarity

“…Interestingly, the performance of MTL-damaged patients deviated from control performance in two ways: first, they reported seeing the Familiar Configurations as figure somewhat less often than controls, and second, they reported seeing the Part-Rearranged Novel Configurations as figure more often than controls. Taken alone, the first finding is consistent with the theoretical view that the PRC of the MTL contains representations of complex configurations Lee et al, 2005;Barense et al, 2005Barense et al, , 2007Barense et al, , 2010a; Bartko et al, 2007;Lee and Rudebeck, 2010;Burke et al, 2011), and damage to these configural representations removes effects of configuration familiarity on figure assignment. Taken together, however, the two findings suggest that either output from the PRC is privileged over that from lower-level visual regions during figure-ground assignment (a feedforward explanation for the data) or that the intact PRC plays a role in modulating processing in lower-level visual areas (a feedback explanation).…”

The loss of short-term visual representations over time: Decay or temporal distinctiveness?

“…Materials. The Fribbles used in this study are abstract and unconventional stimuli that consist of a body and four different appendages (Barense, Gaffan, & Graham, 2007). They have been described as non-nameable due to their complex yet novel appearance (Hartshorne, 2008) Each condition included 18 "same" trials and 18 "different" trials, and stimuli from the full range of Fribble species were included (i.e.…”

Working memory, long-term memory, and medial temporal lobe function

“…The finding was that patients with MTL lesions that included perirhinal cortex were intact in the minimum ambiguity condition and impaired in the intermediate and maximum ambiguity conditions. This result was interpreted to reflect a qualitative difference between the minimum condition (where only single features were relevant to the oddity discrimination) and the other two conditions (where conjunctions of features were relevant) (Barense et al 2007;Graham et al 2010). …”

“…Recent findings in monkeys and in humans with perirhinal cortex lesions have been taken to indicate that perirhinal cortex is needed for visual discrimination tasks when the test items have a high degree of feature ambiguity (Bussey et al 2002;Barense et al 2005Barense et al , 2007Lee et al 2005a,b; but see Clark et al 2011). It has also been suggested that the hippocampus is needed when spatial processing is required, for example, in visual discriminations involving scenes (Lee et al 2005a;Graham et al 2006).…”

“…To illustrate this possibility, the data from Barense et al (2007) have been redrawn in Figure 4 (right) to conform to Figure 3A,B. The idea is that, even though stimuli were presented simultaneously, information nonetheless must be retained in memory as attention shifts back and forth between the stimuli.…”