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Biomedical subjects

Michael J Kahana

Publications and source records attributed to Michael J Kahana.

At least 19 recordsLinked to original sources
PubMed2006

Learning your way around town: how virtual taxicab drivers learn to use both layout and landmark information.

By having subjects drive a virtual taxicab through a computer-rendered town, we examined how landmark and layout information interact during spatial navigation. Subject-drivers searched for passengers, and then attempted to take the most efficient route to the requested destinations (one of several target stores). Experiment 1 demonstrated that subjects rapidly learn to find direct paths from random pickup locations to target stores. Experiment 2 varied the degree to which landmark and layout cues were preserved across two successively learned towns. When spatial layout was preserved, transfer was low if only target stores were altered, and high if both target stores and surrounding buildings were altered, even though in the latter case all local views were changed. This suggests that subjects can rapidly acquire a survey representation based on the spatial layout of the town and independent of local views, but that subjects will rely on local views when present, and are harmed when associations between previously learned landmarks are disrupted. We propose that spatial navigation reflects a hierarchical system in which either layout or landmark information is sufficient for orienting and wayfinding; however, when these types of cues conflict, landmarks are preferentially used.

Adult↗
PubMed2006

EEG oscillations and recognition memory: theta correlates of memory retrieval and decision making.

Studies of memory retrieval have identified electroencephalographic (EEG) correlates of a test item's old-new status, reaction time, and memory load. In the current study, we used a multivariate analysis to disentangle the effects of these correlated variables. During retrieval, power of left-parietal theta (4-8 Hz) oscillations increased in proportion to how well a test item was remembered, and theta in central regions correlated with decision making. We also studied how these oscillatory dynamics complemented event-related potentials. These findings are the first to demonstrate that distinct patterns of theta oscillations can simultaneously relate to different aspects of behavior.

Adult↗
PubMed2006

Hippocampal and neocortical gamma oscillations predict memory formation in humans.

Functional magnetic resonance imaging (fMRI) of the human brain has shown that the hippocampus and the left temporal and frontal cortices play a key role in the formation of new verbal memories. We recorded electrical activity from 2349 surgically implanted intracranial electrodes in epilepsy patients while they studied and later recalled lists of common words. Using these recordings, we demonstrate that gamma oscillations (44-64 Hz) in the hippocampus and the left temporal and frontal cortices predict successful encoding of new verbal memories. This increase in gamma oscillations was not seen in other frequency bands, whose activity generally decreased during successful memory formation. These findings identify a role for gamma oscillations in verbal memory formation with the hippocampus and the left temporal and frontal cortices, the same regions implicated using noninvasive fMRI recording methods.

Adaptation, Physiological↗
PubMed2006

Oscillatory correlates of the primacy effect in episodic memory.

Both intracranial and scalp EEG studies have demonstrated that oscillatory activity, especially in the gamma band (28 to 100 Hz), can differentiate successful and unsuccessful episodic encoding [Sederberg, P.B., Kahana, M.J., Howard, M.W., Donner, E.J., Madsen, J.R., 2003. Theta and gamma oscillations during encoding predict subsequent recall. Journal of Neuroscience, 23(34), 10809-10814; Fell, J., Klaver, P., Lehnertz, K., Grunwald, T., Schaller, C., Elger, C.E., Fernandez, G., 2001. Human memory formation is accompanied by rhinal-hippocampal coupling and decoupling. Nature Neuroscience, 4 (12), 1259-1264; Gruber, T., Tsivilis, D., Montaldi, D., and Müller, M. (2004). Induced gamma band responses: An early marker of memory encoding and retrieval. Neuroreport, 15, 1837-1841; Summerfield, C., Mangels, J.A., in press. Dissociable neural mechanisms for encoding predictable and unpredictable events. Journal of Cognitive Neuroscience]. Although the probability of recalling an item varies as a function of where it appeared in the list, the relation between the oscillatory dynamics of successful encoding and serial position remains unexplored. We recorded scalp EEG as participants studied lists of common nouns in a delayed free-recall task. Because early list items were recalled better than items from later serial positions (the primacy effect), we analyzed encoding-related changes in 2 to 100 Hz oscillatory power as a function of serial position. Increases in gamma power in posterior regions predicted successful encoding at early serial positions; widespread low-frequency (4-14 Hz) power decreases predicted successful memory formation for later serial positions. These results suggest that items in early serial positions receive an encoding boost due to focused encoding without having to divide resources among numerous list items. Later in the list, as memory load increases, encoding is divided between multiple items.

Adult↗
PubMed2006

Human neocortical oscillations exhibit theta phase differences between encoding and retrieval.

We analyzed intracranial brain activity recorded from human participants during the performance of a working-memory task. We show that 6-13 Hz activity exhibits consistent phase across trials following experimental stimuli, and that this phase significantly differs between study and test stimuli. These findings suggest that oscillatory phase reflects the encoding-retrieval state of neural networks, supporting predictions of recent models of memory.[Hasselmo, M.E., Wyble, B.P., and Bodelon, C., 2002. A proposed function for hippocampal theta rhythm: Separate phases of encoding and retrieval enhance reversal of prior learning. Neural Comput. 14 793-817.; Judge, S.J., Hasselmo, M.E., 2004. Theta rhythmic stimulation of stratum lacunosum-moleculare in rat hippocampus contributes to associative LTP at a phase offset in stratum radiatum. J. Neurophys. 92 1516-1624.].

Adolescent↗
PubMed2006

Temporal associations and prior-list intrusions in free recall.

When asked to recall the words from a just-presented target list, subjects occasionally recall words that were not on the list. These intrusions either appeared on earlier lists (prior-list intrusions, or PLIs) or had not appeared over the course of the experiment (extra-list intrusions). The authors examined the factors that elicit PLIs in free recall. A reanalysis of earlier studies revealed that PLIs tend to come from semantic associates as well as from recently studied lists, with the rate of PLIs decreasing sharply with list recency. The authors report 3 new experiments in which some items in a given list also appeared on earlier lists. Although repetition enhanced recall of list items, subjects were significantly more likely to make PLIs following the recall of repeated items, suggesting that temporal associations formed in earlier lists can induce recall errors. The authors interpret this finding as evidence for the interacting roles of associative and contextual retrieval processes in recall. Although contextual information helps to focus recall on words in the target list, it does not form an impermeable boundary between current- and prior-list experiences.

Adolescent↗
PubMed2006

Short-term visual recognition and temporal order memory are both well-preserved in aging.

Increased difficulty with memory for recent events is a well-documented consequence of normal aging, but not all aspects of memory are equally affected. To compare the impact of aging on short-term recognition and temporal order memory, young and older adults were asked to identify the serial position that a probe item had occupied in a study set, or to judge that the probe was novel (had not been in the study set). Stimuli were compound sinusoidal gratings, which resist verbal description and rehearsal. With retention intervals of 1 or 4 seconds, young and older adults produced highly similar overall performance, serial position curves, and proportions of trials on which a correct recognition response was accompanied by an incorrect temporal order judgment. Temporal order errors, which occurred on about one quarter of trials, were traced to two factors: perceptual similarity between the wrongly identified study item and the correct item, and temporal similarity between the wrongly identified item and the correct one. Our results show that short-term visual temporal order memory is well-preserved in normal aging, and when temporal order errors do occur, they arise from similar causes for young and older people.

Adult↗
PubMed2006

Aging and contextual binding: modeling recency and lag recency effects with the temporal context model.

Normal aging has been shown to spare recency effects in the initiation of free recall while disrupting temporally defined associations. The temporal context model (TCM) explains recency and temporally defined associations as consequences of a gradually changing context signal and recovery of those contextual states, respectively. Here we extend TCM to account for the dissociation between recency and temporally defined associations in younger and older adults. Modeling results suggested that the effect of aging was restricted to a decrement in the ability of items to recover the temporal contexts in which they were presented, a function that has been hypothesized to depend on the hippocampus.

Aging↗
PubMed2005

EEG correlates of verbal and nonverbal working memory.

BACKGROUND: Distinct cognitive processes support verbal and nonverbal working memory, with verbal memory depending specifically on the subvocal rehearsal of items. METHODS: We recorded scalp EEG while subjects performed a Sternberg task. In each trial, subjects judged whether a probe item was one of the three items in a study list. Lists were composed of stimuli from one of five pools whose items either were verbally rehearsable (letters, words, pictures of common objects) or resistant to verbal rehearsal (sinusoidal grating patterns, single dot locations). RESULTS: We found oscillatory correlates unique to verbal stimuli in the theta (4-8 Hz), alpha (9-12 Hz), beta (14-28 Hz), and gamma (30-50 Hz) frequency bands. Verbal stimuli generally elicited greater power than did nonverbal stimuli. Enhanced verbal power was found bilaterally in the theta band, over frontal and occipital areas in the alpha and beta bands, and centrally in the gamma band. When we looked specifically for cases where oscillatory power in the time interval between item presentations was greater than oscillatory power during item presentation, we found enhanced beta activity in the frontal and occipital regions. CONCLUSION: These results implicate stimulus-induced oscillatory activity in verbal working memory and beta activity in the process of subvocal rehearsal.

Journal Article↗
PubMed2005

Human hippocampal theta activity during virtual navigation.

This study examines whether 4-8-Hz theta oscillations can be seen in the human hippocampus, and whether these oscillations increase during virtual movement and searching, as they do in rodents. Recordings from both hippocampal and neocortical depth electrodes were analyzed while six epileptic patients played a virtual taxi-driver game. During the game, the patients alternated between searching for passengers, whose locations were random, and delivering them to stores, whose locations remained constant. In both hippocampus and neocortex, theta increased during virtual movement in all phases of the game. Hippocampal and neocortical theta activity were also significantly correlated with each other, but this correlation did not differ between neocortex and hippocampus and within disparate neocortical electrodes. Our findings demonstrate the existence of movement-related theta oscillations in human hippocampus, and suggest that both cortical and hippocampal oscillations play a role in attention and sensorimotor integration.

Adult↗
PubMed2005

Theoretical correlations and measured correlations: relating recognition and recall in four distributed memory models.

This article addresses the relation between item recognition and associative (cued) recall. Going beyond measures of performance on each task, the analysis focuses on the degree to which the contingency between successful recognition and successful recall of a studied item reflects the commonality of memory processes underlying the recognition and recall tasks. Specifically, 4 classes of distributed memory models are assessed for their ability to account for the relatively invariant correlation (approximately .5) between successive recognition and recall. Basic versions of each model either under- or overpredict the intertask correlation. Introducing variability in goodness-of-encoding and response criteria, as well as output encoding, enabled all 4 models to reproduce the moderate intertask correlation and the increase in correlation observed in 2 mixed-list experiments. This model-based analysis provides a general theoretical framework for interpreting contingencies between successive memory tests.

Cues↗
PubMed2005

Intrusions in episodic recall: age differences in editing of overt responses.

Two experiments compared episodic word-list recall of young and older adults. In Experiment 1, using standard free-recall procedures, older adults recalled significantly fewer correct items and made significantly more intrusions (recall of items that had not appeared on the target list) than younger adults. In Experiment 2, we introduced a new method, called externalized free recall, in which participants were asked to recall any items that came to mind during the recall period but to indicate with an immediate key press those items they could identify as intrusions. Both age groups generated a large number of intrusions, but older adults were significantly less likely than young adults to identify these as nonlist items. Results suggest that an editing deficit may be a contributor to age differences in episodic recall and that externalized free recall may be a useful tool for testing computationally explicit models of episodic recall.

Adult↗
PubMed2005

Shadows of the past: temporal retrieval effects in recognition memory.

We examine whether temporally defined associations play a role in item recognition. The role of these associations in recall tasks is well known; we demonstrate an important role in item recognition as well. In this study, subjects were significantly more likely to recognize a test item as having been previously experienced if the preceding test item was studied in a temporally proximal list position than if the preceding test item came from a more distant list position. Further analyses showed that this associative effect was almost entirely due to cases in which the preceding test item received a highest-confidence recognition judgment.

Humans↗
PubMed2005

A comparative analysis of serial and free recall.

Multitrial free and serial recall tasks differ both in recall instruction and in presentation order across trials. Waugh (1961) compared these paradigms with an intermediate condition: free recall with constant presentation order. She concluded that differences between free and serial recall were due only to recall instructions, and not to presentation order. The present study reevaluated the relation between free and serial recall, using Waugh's three conditions. By examining recall transitions and the organization of information retained across trials, we conclude that presentation order is an important factor, causing participants to exhibit the same temporal associations in serial recall and in free recall with constant presentation order.

Adolescent↗
PubMed2005

Spacing and lag effects in free recall of pure lists.

Repeating list items leads to better recall when the repetitions are separated by several unique items than when they are presented successively; the spacing effect refers to improved recall for spaced versus successive repetition (lag > 0 vs. lag = 0); the lag effect refers to improved recall for long lags versus short lags. Previous demonstrations of the lag effect have utilized lists containing a mixture of items with varying degrees of spacing. Because differential rehearsal of items in mixed lists may exaggerate any effects of spacing, it is important to demonstrate these effects in pure lists. As in Toppino and Schneider (1999), we found an overall advantage for recall of spaced lists. We further report the first demonstration of a lag effect in pure lists, with significantly better recall for lists with widely spaced repetitions than for those with moderately spaced repetitions.

Attention↗
PubMed2005

Going beyond a single list: modeling the effects of prior experience on episodic free recall.

We present an extension of the search of associative memory (SAM) model that simulates the effects of both prior semantic knowledge and prior episodic experience on episodic free recall. The model incorporates a memory store for preexisting semantic associations, a contextual drift mechanism, a memory search mechanism that uses both episodic and semantic associations, and a large lexicon including both words from prior lists and unpresented words. These features enabled the model to successfully account for the effects of prior semantic knowledge and prior episodic learning on the pattern of correct recalls and intrusions observed in free recall experiments.

Association↗
PubMed2004

Short-term episodic memory for visual textures: a roving probe gathers some memory.

Cognition is shaped by the way that past experiences are represented in memory. To examine the representation of recent visual experiences, we devised a novel procedure that measures episodic recognition memory for synthetic textures. On each trial, two brief study stimuli were followed by a probe, which either replicated one of the study stimuli or differed in spatial frequency from both. The probe's spatial frequency roved from trial to trial, testing recognition with a range of differences between probe and study items. Repeated testing of recognition generated mnemometric functions, snapshots of memory strength's distribution. The distributional characteristics of the mnemometric functions rule out several hypotheses about memory representation, including the hypothesis that representations are prototypes constructed from previously seen stimuli; instead, stimuli are represented in memory as noisy exemplars.

Adult↗