citation

Warren, D. E., Rubin, R. D., Shune, S., & Duff, M. C. (2018). Memory and language: how their shared cognitive processes, neural correlates, and supporting mechanisms change with age. In M. Rizzo, S. Anderson, & B. Fritzsch (Eds.) The Wiley handbook on the aging mind and brain., chap. .

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WarrenAgeMemoryLanguage.pdf

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pmid

doi

abstract

citation

Spalding, K. N., Schlichting, M. L., Zeithamova, D., Preston, A. R., Tranel, D., Duff, M. C., & Warren, D. E. (2018). Ventromedial prefrontal cortex is necessary for normal associative inference and memory integration. The Journal of Neuroscience, 2501-17.

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SpaldingABCXY.pdf

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pmid

doi

10.1523/JNEUROSCI.2501-17.2018

abstract

citation

Capizzano, A. A., Moritani, T., Jacob, M., & Warren, D. E. (2018). Brain morphologic, chemical and physiologic changes detected with in vivo MRI. In M. Rizzo, S. Anderson, & B. Fritzsch (Eds.) The Wiley handbook on the aging mind and brain., chap. .

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CapizzanoAgeMRI.pdf

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pmid

doi

abstract

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Hannula, D. E., Ryan, J. D., & Warren, D. E. (2017). Beyond long-term declarative memory: evaluating hippocampal contributions to unconscious memory expression, perception, and short-term retention. In D. E. Hannula & M. C. Duff (Eds.) The Hippocampus from Cells to Systems., chap. , (pp. 281-336).

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HannulaHippocampusChapter.pdf

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pmid

doi

10.1007/978-3-319-50406-3_10

abstract

citation

Hanley, J., Warren, D. E., Glass, N., Tranel, D., Karam, M., & Buckwalter, J. (2017). Visual interpretation of plain radiographs in orthopaedics using eye-tracking technology. The Iowa Orthopaedic Journal, 37, 225-31.

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HanleyOrthoXRay.pdf

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pmid

28852362

doi

abstract

citation

Warren, D. E., Kurczek, J., & Duff, M. C. (2016). What relates newspaper, definite, and clothing? An article describing deficits in convergent problem solving and creativity following hippocampal damage. Hippocampus.

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WarrenCreativity2016.pdf

cites

pmid

27010751

doi

10.1002/hipo.22591

abstract

Creativity relies on a diverse set of cognitive processes associated with distinct neural correlates, and one important aspect of creativity, divergent thinking, has been associated with the hippocampus. However, hippocampal contributions to another important aspect of creativity, convergent problem solving, have not been investigated. We tested the necessity of hippocampus for convergent problem solving using a neuropsychological method. Participants with amnesia due to hippocampal damage (N=5) and healthy normal comparison participants (N=5) were tested using a task that promoted solutions based on existing knowledge (Bowden and Jung-Beeman, 2003). During each trial, participants were given a list of three words (e.g., fly, man, place) and asked to respond with a word that could be combined with each of the three words (e.g., fire). The amnesic group produced significantly fewer correct responses than the healthy comparison group. These findings indicate that the hippocampus is necessary for normal convergent problem solving and that changes in the status of the hippocampus should affect convergent problem solving in the context of creative problem-solving across short intervals. This proposed contribution of the hippocampus to convergent problem solving is consistent with an expanded perspective on hippocampal function that acknowledges its role in cognitive processes beyond declarative memory. This article is protected by copyright. All rights reserved.

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Warren, D. E., Power, J. D., Bruss, J., Denburg, N. L., Waldron, E. J., Sun, H., Petersen, S. E., & Tranel, D. (2016). Brain network theory can predict whether neuropsychological outcomes will differ from clinical expectations. Archives of Clinical Neuropsychology, 14247-52.

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WarrenProfileAgreement.pdf

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pmid

27789443

doi

10.1093/arclin/acw091

abstract

citation

Warren, D. E., Tranel, D., & Duff, M. C. (2016). Impaired acquisition of new words after left temporal lobectomy despite normal fast-mapping behavior. Neuropsychologia, 80, 165-75.

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WarrenFastMapLTL2015.pdf

cites

pmid

26617264

doi

10.1016/j.neuropsychologia.2015.11.016

abstract

Word learning has been proposed to rely on unique brain regions including the temporal lobes, and the left temporal lobe appears to be especially important. In order to investigate the role of the left temporal lobe in word learning under different conditions, we tested whether patients with left temporal lobectomies (N=6) could learn novel words using two distinct formats. Previous research has shown that word learning in contrastive fast mapping conditions may rely on different neural substrates than explicit encoding conditions (Sharon et al., 2011). In the current investigation, we used a previously reported word learning task that implemented two distinct study formats (Warren and Duff, 2014): a contrastive fast mapping condition in which a picture of a novel item was displayed beside a picture of a familiar item while the novel item's name was presented aurally ("Click on the numbat."); and an explicit encoding (i.e., control) condition in which a picture of a novel item was displayed while its name was presented aurally ("This is a numbat."). After a delay, learning of the novel words was evaluated with memory tests including three-alternative forced-choice recognition, free recall, cued recall, and familiarity ratings. During the fast-mapping study condition both the left temporal lobectomy and healthy comparison groups performed well, but at test only the comparison group showed evidence of novel word learning. Our findings indicate that unilateral resection of the left temporal lobe including the hippocampus and temporal pole can severely impair word learning, and that fast-mapping study conditions do not promote subsequent word learning in temporal lobectomy populations.

citation

Spalding, K. N., Jones, S. H., Duff, M. C., Tranel, D., & Warren, D. E. (2015). Investigating the neural correlates of schemas: ventromedial prefrontal cortex is necessary for normal schematic influence on memory. Journal of Neuroscience, 35(47), 15746-51.

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SpaldingContextualCongruence2015.pdf

cites

pmid

26609165

doi

10.1523/JNEUROSCI.2767-15.2015

abstract

citation

Kumaran, D., Warren, D. E., & Tranel, D. (2015). Damage to the ventromedial prefrontal cortex impairs learning from observed outcomes. Cerebral Cortex, 25(11), 4504-18.

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KumaranWarrenTranel2015.pdf

cites

pmid

25911415

doi

10.1093/cercor/bhv080

abstract

Individuals learn both from the outcomes of their own internally generated actions ("experiential learning") and from the observation of the consequences of externally generated actions ("observational learning"). While neuroscience research has focused principally on the neural mechanisms by which brain structures such as the ventromedial prefrontal cortex (vmPFC) support experiential learning, relatively less is known regarding how learning proceeds through passive observation. We explored the necessity of the vmPFC for observational learning by testing a group of patients with damage to the vmPFC as well as demographically matched normal comparison and brain-damaged comparison groups--and a single patient with bilateral dorsal prefrontal damage--using several value-learning tasks that required learning from direct experience, observational learning, or both. We found a specific impairment in observational learning in patients with vmPFC damage manifest in the reduced influence of previously observed rewards on current choices, despite a relatively intact capacity for experiential learning. The current study provides evidence that the vmPFC plays a critical role in observational learning, suggests that there are dissociable neural circuits for experiential and observational learning, and offers an important new extension of how the vmPFC contributes to learning and memory.

citation

Guzman-Velez, E., Warren, D. E., Feinstein, J. S., Bruss, J., & Tranel, D. (2015). Dissociable contributions of amygdala and hippocampus to emotion and memory in patients with Alzheimer's disease. Hippocampus.

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GuzmanVelezAD2015.pdf

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pmid

doi

10.1002/hipo.22554

abstract

citation

Yee, L. T. S., Warren, D. E., Voss, J. L., Duff, M. C., Tranel, D., & Cohen, N. J. (2014). The hippocampus uses information just encountered to guide efficient ongoing behavior. Hippocampus, 24(2), 154-64.

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Yee2013.pdf

cites

pmid

doi

10.1002/hipo.22211

abstract

Adaptive ongoing behavior requires using immediate sensory input to guide upcoming actions. Using a novel paradigm with volitional exploration of visuo-spatial scenes, we revealed novel deficits among hippocampal amnesic patients in effective spatial exploration of scenes, indicated by less-systematic exploration patterns than those of healthy comparison subjects. The disorganized exploration by amnesic patients occurred despite successful retention of individual object locations across the entire exploration period, indicating that exploration impairments were not secondary to rapid decay of scene information. These exploration deficits suggest that amnesic patients are impaired in integrating memory for recent actions, which may include information such as locations just visited and scene content, to plan immediately forthcoming actions. Using a novel task that measured the on-line links between sensory input and behavior, we observed the critical role of the hippocampus in modulating ongoing behavior.

citation

Warren, D. E., Duff, M. C., Cohen, N. J., & Tranel, D. (2014). Hippocampus contributes to the maintenance but not the quality of visual information over time. Learning & Memory, 22(1), 6-10.

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Warren2014ColorWheel.pdf

cites

pmid

25512572

doi

10.1101/lm.037127.114

abstract

The hippocampus has recently been implicated in the brief representation of visual information, but its specific role is not well understood. We investigated this role using a paradigm that distinguishes quantity and quality of visual memory as described in a previous study. We found that amnesic patients with bilateral hippocampal damage (N = 5) were less likely to remember test stimuli than comparison participants despite a brief maintenance interval (900 msec). However, estimates of memory quality were similar for all groups. Our findings suggest that the hippocampus contributes to brief maintenance of visual information but does not contribute to the quality of that information.

citation

Warren, D. E., Jones, S. H., Duff, M. C., & Tranel, D. (2014). False recall is reduced by damage to the ventromedial prefrontal cortex: implications for understanding the neural correlates of schematic memory. Journal of Neuroscience, 34(22), 7677-82.

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WarrenDRMvmPFC.pdf

cites

pmid

24872571

doi

10.1523/JNEUROSCI.0119-14.2014

abstract

Schematic memory, or contextual knowledge derived from experience (Bartlett, 1932), benefits memory function by enhancing retention and speeding learning of related information (Bransford and Johnson, 1972; Tse et al., 2007). However, schematic memory can also promote memory errors, producing false memories. One demonstration is the "false memory effect" of the Deese-Roediger-McDermott (DRM) paradigm (Roediger and McDermott, 1995): studying words that fit a common schema (e.g., cold, blizzard, winter) often produces memory for a nonstudied word (e.g., snow). We propose that frontal lobe regions that contribute to complex decision-making processes by weighting various alternatives, such as ventromedial prefrontal cortex (vmPFC), may also contribute to memory processes by weighting the influence of schematic knowledge. We investigated the role of human vmPFC in false memory by combining a neuropsychological approach with the DRM task. Patients with vmPFC lesions (n = 7) and healthy comparison participants (n = 14) studied word lists that excluded a common associate (the critical item). Recall and recognition tests revealed expected high levels of false recall and recognition of critical items by healthy participants. In contrast, vmPFC patients showed consistently reduced false recall, with significantly fewer intrusions of critical items. False recognition was also marginally reduced among vmPFC patients. Our findings suggest that vmPFC increases the influence of schematically congruent memories, a contribution that may be related to the role of the vmPFC in decision making. These novel neuropsychological results highlight a role for the vmPFC as part of a memory network including the medial temporal lobes and hippocampus (Andrews-Hanna et al., 2010).

citation

Warren, D. E., Power, J. D., Bruss, J., Denburg, N. L., Waldron, E. J., Sun, H., Petersen, S. E., & Tranel, D. (2014). Network measures predict neuropsychological outcome after brain injury. Proceedings of the National Academy of Sciences of the United States of America, 111(39), 14247-52.

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WarrenCNN.pdf

cites

pmid

25225403

doi

10.1073/pnas.1322173111

abstract

Hubs are network components that hold positions of high importance for network function. Previous research has identified hubs in human brain networks derived from neuroimaging data; however, there is little consensus on the localization of such hubs. Moreover, direct evidence regarding the role of various proposed hubs in network function (e.g., cognition) is scarce. Regions of the default mode network (DMN) have been frequently identified as "cortical hubs" of brain networks. On theoretical grounds, we have argued against some of the methods used to identify these hubs and have advocated alternative approaches that identify different regions of cortex as hubs. Our framework predicts that our proposed hub locations may play influential roles in multiple aspects of cognition, and, in contrast, that hubs identified via other methods (including salient regions in the DMN) might not exert such broad influence. Here we used a neuropsychological approach to directly test these predictions by studying long-term cognitive and behavioral outcomes in 30 patients, 19 with focal lesions to six "target" hubs identified by our approaches (high system density and participation coefficient) and 11 with focal lesions to two "control" hubs (high degree centrality). In support of our predictions, we found that damage to target locations produced severe and widespread cognitive deficits, whereas damage to control locations produced more circumscribed deficits. These findings support our interpretation of how neuroimaging-derived network measures relate to cognition and augment classic neuroanatomically based predictions about cognitive and behavioral outcomes after focal brain injury.

citation

Warren, D. E. & Duff, M. C. (2014). Not so fast: hippocampal amnesia slows word learning despite successful fast mapping. Hippocampus, 24(8), 920-33.

pdf

WarrenFastMapAmnesic.pdf

cites

pmid

24719218

doi

10.1002/hipo.22279

abstract

The human hippocampus is widely believed to be necessary for the rapid acquisition of new declarative relational memories. However, processes supporting on-line inferential word use ("fast mapping") may also exercise a dissociable learning mechanism and permit rapid word learning without the hippocampus (Sharon et al., 2011). We investigated fast mapping in severely amnesic patients with hippocampal damage (N=4), mildly amnesic patients (N=6), and healthy comparison participants (N=10) using on-line measures (eye movements) that reflected ongoing processing. All participants studied unique word-picture associations in two encoding conditions. In the explicit-encoding condition, uncommon items were paired with their names (e.g., "This is a numbat."). In the fast mapping study condition, participants heard an instruction using a novel word (e.g., "Click on the numbat.") while two items were presented (an uncommon target such as a numbat, and a common distracter such as a dog). All groups performed fast mapping well at study, and on-line eye movement measures did not reveal group differences. However, while comparison participants showed robust word learning irrespective of encoding condition, severely amnesic patients showed no evidence of learning after fast mapping or explicit encoding on any behavioral or eye-movement measure. Mildly amnesic patients showed some learning, but performance was unaffected by encoding condition. The findings are consistent with the following propositions: the hippocampus is not essential for on-line fast mapping of novel words; but is necessary for the rapid learning of arbitrary relational information irrespective of encoding conditions.

citation

Monti, J. M., Balota, D. A., Warren, D. E., & Cohen, N. J. (2014). Very mild Alzheimer's disease is characterized by increased sensitivity to mnemonic interference. Neuropsychologia, 59, 47-56.

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MontiTTRV.pdf

cites

pmid

doi

10.1016/j.neuropsychologia.2014.04.007

abstract

Early pathology and tissue loss in Alzheimer's disease (AD) occurs in the hippocampus, a brain region that has recently been implicated in relational processing irrespective of delay. Thus, tasks that involve relational processing will especially tax the hippocampal memory system, and should be sensitive to even mild dysfunction typical of early AD. Here we used a short-lag, short-delay memory task previously shown to be sensitive to hippocampal integrity in an effort to discriminate cognitive changes due to healthy aging from those associated with very mild AD. Young adults, healthy older adults, and individuals with very mild AD (N=30 for each group) participated in our investigation, which entailed attempting to find an exact match to a previously presented target among a series of stimuli that varied in perceptual similarity to the target stimulus. Older adults with very mild AD were less accurate than healthy older adults, who, in turn, were impaired relative to young adults. Older adults with very mild AD were also particularly susceptible to interference from intervening lure stimuli. A measure based on this finding was able to explain additional variance in differentiating those in the very mild stage of AD from healthy older adults after accounting for episodic memory and global cognition composite scores in logistic regression models. Our findings suggest that cognitive changes in early stage AD reflect aging along with an additional factor potentially centered on sensitivity to interference, thereby supporting multifactorial models of aging.

citation

Watson, P. D., Voss, J. L., Warren, D. E., Tranel, D., & Cohen, N. J. (2013). Spatial reconstruction by patients with hippocampal damage is dominated by relational memory errors. Hippocampus, 23(7), 570-80.

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Watson2013.pdf

cites

pmid

doi

10.1002/hipo.22115

abstract

Hippocampal damage causes profound yet circumscribed memory impairment across diverse stimulus types and testing formats. Here, within a single test format involving a single class of stimuli, we identified different performance errors to better characterize the specifics of the underlying deficit. The task involved study and reconstruction of object arrays across brief retention intervals. The most striking feature of patients' with hippocampal damage performance was that they tended to reverse the relative positions of item pairs within arrays of any size, effectively "swapping" pairs of objects. These "swap errors" were the primary error type in amnesia, almost never occurred in healthy comparison participants, and actually contributed to poor performance on more traditional metrics (such as distance between studied and reconstructed location). Patients made swap errors even in trials involving only a single pair of objects. The selectivity and severity of this particular deficit creates serious challenges for theories of memory and hippocampus.

citation

Warren, D. E., Thurtell, M. J., Carroll, J. N., & Wall, M. (2013). Perimetric evaluation of saccadic latency, saccadic accuracy, and visual threshold for peripheral visual stimuli in young compared with older adults. Investigative Ophthalmology & Visual Science, 54(8), 5778-87.

pdf

WarrenEMP2013.pdf

cites

pmid

23882693

doi

10.1167/iovs.13-12032

abstract

citation

Warren, D. E., Duff, M. C., Magnotta, V., Capizzano, A. A., Cassell, M. D., & Tranel, D. (2012). Long-term neuropsychological, neuroanatomical, and life outcome in hippocampal amnesia. The Clinical Neuropsychologist, 26(2), 335-69.

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Warren2012.pdf

cites

pmid

doi

10.1080/13854046.2012.655781

abstract

Focal bilateral hippocampal damage typically causes severe and selective amnesia for new declarative information (facts and events), a cognitive deficit that greatly impacts the ability to live a normal, fully independent life. We describe the case of 1846, a 48-year-old woman with profound hippocampal amnesia following status epilepticus and an associated anoxic episode at age 30. Patient 1846 has undergone extensive neuropsychological testing on many occasions over the 18 years since her injury, and we present data indicating that her memory impairment has remained severe and stable during that time. New, high-resolution, structural MRI studies of 1846's brain reveal substantial bilateral hippocampal atrophy resembling that of other well-known amnesic patients. In spite of severe amnesia 1846 lives a full and mostly independent adult life, facilitated by an extensive social support network of family and friends. Her case provides an example of a rare and unlikely positive outcome in the face of severe memory problems.

citation

Warren, D. E., Duff, M. C., Jensen, U., Tranel, D., & Cohen, N. J. (2012). Hiding in plain view: lesions of the medial temporal lobe impair online representation. Hippocampus, 22(7), 1577-88.

pdf

Warren2012a.pdf

cites

pmid

22180166

doi

10.1002/hipo.21000

abstract

The hippocampus is necessary for the normal formation of enduring declarative memories, but its role in cognitive processes spanning short intervals is less well understood. Within the last decade, several reports have described modest behavioral deficits in medial temporal lobe (MTL)-lesion patients when they perform tasks that do not seem likely to rely on enduring memory. An intriguing but sparsely-tested implication of such results is that the MTL is involved in the online representation of information, possibly of an associative/relational nature, irrespective of delay. We administered several tests that simultaneously presented all information necessary for accurate responses to a group of MTL-lesion patients with severe declarative memory deficits but otherwise normal cognition, and to matched brain-damaged and healthy comparison participants. MTL-lesion patients performed less well than either comparison group in the Hooper Visual Organization Test, and several patients performed outside the normal range on the Overlapping Figures Test. A novel follow-up borrowing characteristics of the Overlapping Figures Test revealed impaired identification of novel items by MTL-lesion patients when target items were obscured by distracters, and two additional novel tests of fragmented object identification further implicated the hippocampus/MTL in the integration of information across very brief intervals. These findings suggest that MTL structures including the hippocampus contribute similarly to cognition irrespective of timescale.

citation

Hannula, D. E., Baym, C. L., Warren, D. E., & Cohen, N. J. (2012). The eyes know: eye movements as a veridical index of memory. Psychological Science, 23(3), 278-87.

pdf

Hannula2012.pdf

cites

pmid

22327015

doi

10.1177/0956797611429799

abstract

In two experiments, we examined whether observers' eye movements distinguish studied faces from highly similar novel faces. Participants' eye movements were monitored while they viewed three-face displays. Target-present displays contained a studied face and two morphed faces that were visually similar to it; target-absent displays contained three morphed faces that were visually similar to a studied, but not tested, face. On each trial in a test session, participants were instructed to choose the studied face if it was present or a random face if it was not and then to indicate whether the chosen face was studied. Whereas manipulating visual similarity in target-absent displays influenced the rate of false endorsements of nonstudied items as studied, eye movements proved impervious to this manipulation. Studied faces were viewed disproportionately from 1,000 to 2,000 ms after display onset and from 1,000 to 500 ms before explicit identification. Early viewing also distinguished studied faces from faces incorrectly endorsed as studied. Our findings show that eye movements provide a relatively pure index of past experience that is uninfluenced by explicit response strategies, and suggest that eye movement measures may be of practical use in applied settings.

citation

Duff, M. C., Warren, D. E., Gupta, R., Vidal, J. P. B., Tranel, D., & Cohen, N. J. (2012). Teasing apart tangrams: Testing hippocampal pattern separation with a collaborative referencing paradigm. Hippocampus, 22(5), 1087-91.

pdf

Duff2012.pdf

cites

pmid

21830250

doi

10.1002/hipo.20967

abstract

The hippocampus and the medial temporal lobe cortex [medial temporal lobe cortices (MTLC)] both contribute to long-term memory. Although their contributions are thought to be dissociable, the nature of the representations that each region supports remains unclear. The Complementary Learning Systems (CLS) modeling approach suggests that hippocampus represents overlapping information in a sparser and therefore more separated fashion than MTLC. We tested this prediction using a collaborative referencing paradigm whereby hippocampal amnesic patients and a partner work together to develop and use unique labels for a set of abstract visual stimuli (tangrams) across extended interactions. Previously, we reported that amnesic patients demonstrate intact learning when the tangrams are conceptually dissimilar. Here, we manipulated the degree of visual similarity; half of the stimuli were dissimilar to one another (e.g., camel and giraffe), and half were similar (e.g., birds). We hypothesized that while patients would have little difficulty with the dissimiliar tangrams (quickly arriving at unique and concise labels), they would be unable to rapidly form distinct representations of highly similar visual patterns. Consistent with this prediction, patients and both healthy and brain-damaged comparison participants showed similar rates of learning for dissimilar tangrams, but the similar tangrams proved more difficult for hippocampal patients as reflected in the greater number of words they used to describe each similar card. This result supports the CLS model's central claim of hippocampal specialization for pattern separation and suggests that our collaborative referencing paradigm may be a useful tool for observing extended encoding of complex representations.

citation

Coronel, J. C., Duff, M. C., Warren, D. E., Federmeier, K. D., Gonsalves, B. D., Tranel, D., & Cohen, N. J. (2012). Remembering and voting: theory and evidence from amnesic patients. American journal of political science, 56(4), 837-48.

pdf

Coronel2012.pdf

cites

pmid

doi

10.1111/j.1540-5907.2012.00608.x

abstract

One of the most prominent claims to emerge from the field of public opinion is that citizens can vote for candidates whose issue positions best reflect their own beliefs even when they cannot remember previously learned stances associated with the candidates. The current experiment provides a unique and powerful examination of this claim by determining whether individuals with profound amnesia, whose severe memory impairments prevent them from remembering specific issue information associated with any particular candidate, can vote for candidates whose issue positions come closest to their own political views. We report here that amnesic patients, despite not being able to remember any issue information, consistently voted for candidates with favored political positions. Thus, sound voting decisions do not require recall or recognition of previously learned associations between candidates and their issue positions. This result supports a multiple memory systems model of political decision making.

citation

Warren, D. E., Duff, M. C., Tranel, D., & Cohen, N. J. (2011). Observing degradation of visual representations over short intervals when medial temporal lobe is damaged. Journal of Cognitive Neuroscience, 23(12), 3862-73.

pdf

Warren2011.pdf

cites

pmid

21736458

doi

10.1162/jocn_a_00089

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.

citation

Voss, J. L., Warren, D. E., Gonsalves, B. D., Federmeier, K. D., Tranel, D., & Cohen, N. J. (2011). Spontaneous revisitation during visual exploration as a link among strategic behavior, learning, and the hippocampus. Proceedings of the National Academy of Sciences of the United States of America, 108(31), E402-409.

pdf

Voss2011.pdf

cites

pmid

21768385

doi

10.1073/pnas.1100225108

abstract

Effective exploratory behaviors involve continuous updating of sensory sampling to optimize the efficacy of information gathering. Despite some work on this issue in animals, little information exists regarding the cognitive or neural mechanisms for this sort of behavioral optimization in humans. Here we examined a visual exploration phenomenon that occurred when human subjects studying an array of objects spontaneously looked "backward" in their scanning paths to view recently seen objects again. This "spontaneous revisitation" of recently viewed objects was associated with enhanced hippocampal activity and superior subsequent memory performance in healthy participants, but occurred only rarely in amnesic patients with severe damage to the hippocampus. These findings demonstrate the necessity of the hippocampus not just in the aspects of long-term memory with which it has been associated previously, but also in the short-term adaptive control of behavior. Functional neuroimaging showed hippocampal engagement occurring in conjunction with frontocerebellar circuits, thereby revealing some of the larger brain circuitry essential for the strategic deployment of information-seeking behaviors that optimize learning.

citation

Warren, D. E., Duff, M. C., Tranel, D., & Cohen, N. J. (2010). Medial temporal lobe damage impairs representation of simple stimuli. Frontiers in Human Neuroscience, 4, 1-9.

pdf

Warren2010a.pdf

cites

pmid

20508745

doi

10.3389/fnhum.2010.00035

abstract

Medial temporal lobe (MTL) damage in humans is typically thought to produce a circumscribed impairment in the acquisition of new enduring memories, but recent reports have documented deficits even in short-term maintenance. We examined possible maintenance deficits in a population of MTL amnesics, with the goal of characterizing their impairments as either representational drift or outright loss of representation over time. Patients and healthy comparisons performed a visual search task in which the similarity of various lures to a target was varied parametrically. Stimuli were simple shapes varying along one of several visual dimensions. The task was performed in two conditions, one presenting a sample target simultaneously with the search array and the other imposing a delay between sample and array. Eye-movement data collected during search revealed that the duration of fixations to items varied with lure-target similarity for all participants, i.e., fixations were longer for items more similar to the target. In the simultaneous condition, patients and comparisons exhibited an equivalent effect of similarity on fixation durations. However, imposing a delay modulated the effect differently for the two groups: in comparisons, fixation duration to similar items was exaggerated; in patients, the original effect was diminished. These findings indicate that MTL lesions subtly impair short-term maintenance of even simple stimuli, with performance reflecting not the complete loss of the maintained representation but rather a degradation or progressive drift of the representation over time.

citation

Hannula, D. E., Althoff, R. R., Warren, D. E., Riggs, L., Cohen, N. J., & Ryan, J. D. (2010). Worth a glance: using eye movements to investigate the cognitive neuroscience of memory. Frontiers in Human Neuroscience, 4, 52-67.

pdf

Hannula2010.pdf

cites

pmid

21151363

doi

10.3389/fnhum.2010.00166

abstract

Results of several investigations indicate that eye movements can reveal memory for elements of previous experience. These effects of memory on eye movement behavior can emerge very rapidly, changing the efficiency and even the nature of visual processing without appealing to verbal reports and without requiring conscious recollection. This aspect of eye movement based memory investigations is particularly useful when eye movement methods are used with special populations (e.g., young children, elderly individuals, and patients with severe amnesia), and also permits use of comparable paradigms in animals and humans, helping to bridge different memory literatures and permitting cross-species generalizations. Unique characteristics of eye movement methods have produced findings that challenge long-held views about the nature of memory, its organization in the brain, and its failures in special populations. Recently, eye movement methods have been successfully combined with neuroimaging techniques such as fMRI, single-unit recording, and magnetoencephalography, permitting more sophisticated investigations of memory. Ultimately, combined use of eye-tracking with neuropsychological and neuroimaging methods promises to provide a more comprehensive account of brain-behavior relationships and adheres to the "converging evidence" approach to cognitive neuroscience.

citation

Konkel, A., Warren, D. E., Duff, M. C., Tranel, D. N., & Cohen, N. J. (2008). Hippocampal amnesia impairs all manner of relational memory. Frontiers in Human Neuroscience, 2, 1-5.

pdf

Konkel2008.pdf

cites

pmid

18989388

doi

10.3389/neuro.09.015.2008

abstract

Relational memory theory holds that the hippocampus supports, and amnesia following hippocampal damage impairs, memory for all manner of relations. Unfortunately, many studies of hippocampal-dependent memory have either examined only a single type of relational memory or conflated multiple kinds of relations. The experiments reported here employed a procedure in which each of several kinds of relational memory (spatial, associative, and sequential) could be tested separately using the same materials. In Experiment 1, performance of amnesic patients with medial temporal lobe (MTL) damage was assessed on memory for the three types of relations as well as for items. Compared to the performance of matched comparison participants, amnesic patients were impaired on all three relational tasks. But for those patients whose MTL damage was limited to the hippocampus, performance was relatively preserved on item memory as compared to relational memory, although still lower than that of comparison participants. In Experiment 2, study exposure was reduced for comparison participants, matching their item memory to the amnesic patients in Experiment 1. Relational memory performance of comparison subjects was well above amnesic patient levels, showing the disproportionate dependence of all three relational memory performances on the integrity of the hippocampus. Correlational analyses of the various task performances of comparison participants and of college-age participants showed that our measures of item memory were not influenced significantly by memory for associations among the items.

citation

Simons, D. J., Hannula, D. E., Warren, D. E., & Day, S. W. (2007). Behavioral, neuroimaging, and neuropsychological approaches to implicit perception. In P. Zelano, M. Moscovitch, & E. Thompson (Eds.) Cambridge Handbook of Consciousness., chap. , (pp. 207-50).

pdf

Simons2006.pdf

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abstract