Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2011 Dec;23(12):3862-73.
doi: 10.1162/jocn_a_00089. Epub 2011 Jul 7.

Observing Degradation of Visual Representations Over Short Intervals When Medial Temporal Lobe Is Damaged

Affiliations
Free PMC article

Observing Degradation of Visual Representations Over Short Intervals When Medial Temporal Lobe Is Damaged

David E Warren et al. J Cogn Neurosci. .
Free PMC article

Abstract

Medial temporal lobe (MTL) contributions to the brief maintenance of visual representations were evaluated by studying a group of patients with MTL damage. Eye movements of patients and healthy comparison subjects were tracked while performing a visual search for a target among complex stimuli of varying similarity to that target. Despite the task having no imposed delays, patients were impaired behaviorally, and eye movement measures showed abnormally rapid degradation of target representations in the patients. Eye movement data showed a modulation of the duration of fixations as a function of the similarity of fixated array lures to the target, but the effect was attenuated in patients during long fixation paths away from the sample target. This effect manifested despite patients' shorter searches and more frequent fixations of the sample target. Novel techniques provided unique insight into visual representation without healthy MTL, which may support maintenance of information through hippocampal-dependent relational binding.

Figures

Figure 1
Figure 1
Illustrations of selected items and sample displays. (a) Three sample items illustrating the three-wedge design of all targets and lures, and the three components that occurred in the top left, top right, and bottom portions of the items. (b) and (c) Illustrations of target-present and target-absent test displays, respectively. Subjects searched each test display for an item that matched the central sample, responding “Yes” if they found a target and “No” if they did not. In (b) the target is located in row 2, column 7.
Figure 2
Figure 2
Summary of the behavioral data. (a) MTL patients were reliably impaired at search relative to comparisons, and their scores are individually labeled for reference. (b) All subjects searched more quickly as the experiment continued, although patients were slower than comparisons overall. Individual response times and best-fit regression lines are shown.
Figure 3
Figure 3
Modulation of fixation duration by lure-sample similarity. Note that the y-axes of all three panels use ln(ms) units, but that (a) uses a different scale than (b) and (c), which both plot differences in fixation durations rather than whole fixation durations. (a) Both comparisons and MTL patients fixated items that resembled the sample for longer than those that did not. Whiskers indicate standard error of the mean. (b) and (c) However, as more fixations intervened between the last viewing of the sample item and the fixation of a given lure, this effect was attenuated in patients and exaggerated in comparisons; these plots illustrate the effect using the difference in fixation durations between 2- and 0-match lures early and late in search. Group means are presented as bars, while the difference observed for each subject is plotted as a point, and patient values are individually labeled for reference. (b) summarizes data from the entire experiment, while (c) summarizes data from only the first third of the experiment (i.e., 27 trials). * indicates reliable differences at p < 0.05: differences between levels of lure-sample similarity in (a); and reliable MTL status by latency interactions in (b) and (c).
Figure 4
Figure 4
Evidence of learning across the course of the experiment as reflected in eye-movement measures. Both plots show individual values and best-fit regression functions. (a) Comparisons fixated the sample item less and less frequently as the experiment continued, while MTL patients continued fixating the sample item at approximately the same rate throughout. (b) Likewise, comparisons made longer and longer forays from the sample item across the course of the experiment, fixating more items before returning. The lengths of patients’ search paths were stable across the entire experiment.

Similar articles

See all similar articles

Cited by 33 articles

See all "Cited by" articles

Publication types

LinkOut - more resources

Feedback