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Biomedical subjects

M A Gluck

Publications and source records attributed to M A Gluck.

At least 19 recordsLinked to original sources
PubMed2000

Latent learning in medial temporal amnesia: evidence for disrupted representational but preserved attentional processes.

Damage to the hippocampus and medial temporal (MT) structures can lead to anterograde amnesia and may also impair latent learning, in which prior exposure to cues affects their subsequent associability. Normally, latent learning may reflect both representational and attentional mechanisms. Prior work has suggested that individuals with MT amnesia have specific deficits in representational processing; thus, latent learning that invokes primarily representational mechanisms might be especially impaired in MT amnesia. The current results provide preliminary confirmation of this prediction. In Experiment 1, a latent learning paradigm expected to invoke representational mechanisms was impaired in individuals with MT amnesia, whereas in Experiment 2, a paradigm expected to invoke other attentional mechanisms was spared in individuals with MT amnesia. This suggests the representational and attentional components of latent learning are dissociable and differentially affected in anterograde amnesia.

Adult↗
PubMed2000

Stimulus exposure effects in human associative learning.

Learning that one cue (CS) predicts a second, salient cue (US) can often be slowed by prior exposure to one or both stimuli. In animals, CS-US learning is more strongly retarded following uncorrelated exposure to both CS and US than following exposure to the US alone. In this paper we present several studies showing a similar effect in humans, using a computer-based task. Experiments 1 and 2 used a between-groups design and demonstrated a strong CS/US exposure effect, whether or not the US was signalled by a neutral cue during exposure. Experiment 3 demonstrated similar effects using a within-subjects design. Overall, these results are consistent with several theoretical interpretations and suggest that uncorrelated CS/US exposure leads to a robust retardation of subsequent CS-US learning in humans.

Acoustic Stimulation↗
PubMed2000

Nonlinear autoassociation is not equivalent to PCA.

A common misperception within the neural network community is that even with nonlinearities in their hidden layer, autoassociators trained with backpropagation are equivalent to linear methods such as principal component analysis (PCA). Our purpose is to demonstrate that nonlinear autoassociators actually behave differently from linear methods and that they can outperform these methods when used for latent extraction, projection, and classification. While linear autoassociators emulate PCA, and thus exhibit a flat or unimodal reconstruction error surface, autoassociators with nonlinearities in their hidden layer learn domains by building error reconstruction surfaces that, depending on the task, contain multiple local valleys. This interpolation bias allows nonlinear autoassociators to represent appropriate classifications of nonlinear multimodal domains, in contrast to linear autoassociators, which are inappropriate for such tasks. In fact, autoassociators with hidden unit nonlinearities can be shown to perform nonlinear classification and nonlinear recognition.

Linear Models↗
PubMed2000

Dissociating entorhinal and hippocampal involvement in latent inhibition.

This study used anatomical cues to suggest a functional dissociation between the roles of the entorhinal cortex and the hippocampus in learning. The authors proposed that the highly convergent inputs to the entorhinal cortex indicate this region may be particularly important for selecting or compressing information. This hypothesis was tested in rabbits (Oryctolagus cunniculus) trained on an associative learning task that is a common index of stimulus selection. In this task, known as latent inhibition, preexposure to a stimulus (such as a tone) leads to slowed learning when the same tone is subsequently paired with an outcome (such as an airpuff to the eye). As hypothesized, rabbits with neurotoxic lesions of the entorhinal cortex failed to show slowed learning following preexposure (no latent inhibition) and learned the association faster than control rabbits. In contrast, hippocampal-lesioned animals showed normal (slowed) learning.

Animals↗
PubMed1997

Psychobiological models of hippocampal function in learning and memory.

We review current computational models of hippocampal function in learning and memory, concentrating on those that make strongest contact with psychological issues and behavioral data. Some models build upon Marr's early theories for modeling hippocampal field CA3's putative role in the fast, temporary storage of episodic memories. Other models focus on hippocampal involvement in incrementally learned associations, such as classical conditioning. More recent efforts have attempted to bring functional interpretations of the hippocampal region in closer contact with underlying anatomy and physiology. In reviewing these psychobiological models, three major themes emerge. First, computational models provide the conceptual glue to bind together data from multiple levels of analysis. Second, models serve as important tools to integrate data from both animal and human studies. Third, previous psychological models that capture important behavioral principles of memory provide an important top-down constraint for developing computational models of the neural bases of these behaviors.

Animals↗
PubMed1996

Integrating behavioral and physiological models of hippocampal function.

In recent modeling of hippocampal function, we have attempted to integrate formal behavioral analyses of classical conditioning with psychobiological data on brain lesions (Gluck and Myers [1993] Hippocampus 3:491-516; Myers and Gluck [1994] Behav Neurosci 108(5):835-847). Based on comparative behavioral analyses, we have argued that animals with hippocampal region damage are unable to alter stimulus similarity based on experience. While hippocampal-damaged animals can still learn whether to respond to an individual stimulus, they are notably impaired at many tasks involving learning relationships between stimuli-especially in the absence of explicit reinforcement. These analyses lead to a computational theory which identifies two representational recoding processes-predictive differentiation and redundancy compression-which alter stimulus similarity relationships in intact animals but are dependent on intact hippocampal region processing. More recent, and ongoing, modeling aims to broaden this model of hippocampal region function in classical conditioning, with an emphasis on physiological and anatomical constraints, including the role of the fornix and subcortical modulation, preprocessing in sensory cortices, and localization of the proposed representational functions within more precisely identified hippocampal region substrates (Myers et al. [1995] Psychology 23(2):116-138; Myers and Gluck [1996] Behav Neurosci; Myers et al. [1996] Neurobiol Learning Memory). Working to bridge between behavioral and physiological levels of analysis, we ultimately hope to develop a more complete understanding of hippocampal region function in memory across a wider range of behavioral paradigms, elucidating how this functionality emerges from underlying physiological and anatomical substrates.

Amnesia↗
PubMed1996

A computational model of cholinergic disruption of septohippocampal activity in classical eyeblink conditioning.

A previous neurocomputational model of corticohippocampal interaction (Gluck & Myers, 1993) can provide a framework for examining the behavioral effects of septohippocampal modulation during classical conditioning. The model assumes that the hippocampal region is necessary for forming new stimulus representations during learning, but not for the formation of simple associations. This paper considers how septohippocampal interaction could affect this function. The septal nuclei provide several modulatory inputs to the hippocampus, including a cholinergic input which Hasselmo (1995) has suggested may function to regulate hippocampal dynamics on a continuum between two states: a storage state in which incoming information is encoded as an intermediate-term memory and a recall state when this information is reactivated. In this theory, anticholinergic drugs such as scopolamine should disrupt learning by selectively reducing the hippocampus's ability to store new information. An approximation of Hasselmo's idea can be implemented in the corticohippocampal model by a simple manipulation of hippocampal learning rate; this manipulation is formally equivalent to adjusting the amount of time the hippocampus spends in learning and recall states. With this manipulation, the model successfully accounts for the effects of scopolamine in retarding classical conditioning in humans (Solomon, Groccia-Ellison, Flynn, Mirak, Edwards, Dunehew, & Stanton, 1993) and animals (Solomon, Soloman, van der Schaaf, & Perry, 1983). The model further predicts that although cholinergic agonists (such as Tacrine) may improve learning in subjects with artificially depressed brain acetylcholine levels, there may be limited memory improvement in normal subjects from such cholinergic therapy. This is consistent with the general finding of a U-shaped dose response curve for cholinergic drugs in normal subjects: low to moderate doses may improve learning, but higher doses are ineffective or even degrade learning (e.g., Ennaceur & Meliani, 1992; Dumery, Derer, & Blozovski, 1988; etc.).

Animals↗
PubMed1996

Cortico-hippocampal representations in simultaneous odor discrimination: a computational interpretation of Eichenbaum, Mathews, and Cohen (1989).

A previous model of hippocampal region function in classical conditioning is generalized to H. Eichenbaum, A. Fagan, P. Mathews, and N.J. Cohen's (1989) and H. Eichenbaum, A. Fagan, and N.J. Cohen's (1989) simultaneous odor discrimination studies in rats. The model assumes that the hippocampal region forms new stimulus representations that compress redundant information while differentiating predictie information; the piriform (olfactory) cortex meanwhile clusters similar and co-occurring odors. Hippocampal damage interrupts the ability to differentiate odor representations, while leaving piriform-mediated odor clustering unchecked. The result is a net tendency to overcompress in the lesioned model. Behavior in the model is very similar to that of the rats, including lesion deficits, facilitation of successively learned tasks, and transfer performance. The computational mechanisms underlying model performance are consistent with the qualitative interpretations suggested by Eichen baum et al. to explain their empirical data.

Animals↗
PubMed1995

Intact delay-eyeblink classical conditioning in amnesia.

The status of classical conditioning in human amnesia was examined by comparing conditioning of the eyeblink response (the unconditional response) to a tone conditioned stimulus (CS) paired with an airpuff unconditioned stimulus (US) in the delay paradigm between 7 amnesic and 7 age- and education-matched normal control participants. Amnesic patients exhibited normal baseline performance in pseudoconditioning and normal acquisition and extinction of conditioned responses in terms of the number, latency, and magnitude of eyeblinks. These results indicate that in humans, as in rabbits, brain structures critical for declarative memory are not essential for the acquisition of elementary CS-US associations.

Adult↗
PubMed1994

Context, conditioning, and hippocampal rerepresentation in animal learning.

The researchers argue that a previous computational account of hippocampal region function in associative learning (M. Gluck & C. Myers, 1993) has emergent implications that accurately describe the role of the hippocampal region in contextual processing. This article unifies 2 seemingly conflicting views of contextual processing: It accords contextual cues no special representational status (e.g., R. Rescorla & A. Wagner, 1972), yet it also allows context to stand in a superordinate relationship to the cues it contains (e.g., L. Nadel & J. Willner, 1980). As a result, the account correctly expects that context can develop occasion-setting properties and that context shifts can weaken learned responses or attenuate latent inhibition. The article also explains data suggesting that hippocampal lesions reduce contextual sensitivity. It may help unify several previous theoretical accounts of the hippocampal region's role in contextual processing.

Animals↗
PubMed1994

Comparing models of rule-based classification learning: a replication and extension of Shepard, Hovland, and Jenkins (1961).

We partially replicate and extend Shepard, Hovland, and Jenkins's (1961) classic study of task difficulty for learning six fundamental types of rule-based categorization problems. Our main results mirrored those of Shepard et al., with the ordering of task difficulty being the same as in the original study. A much richer data set was collected, however, which enabled the generation of block-by-block learning curves suitable for quantitative fitting. Four current computational models of classification learning were fitted to the learning data: ALCOVE (Kruschke, 1992), the rational model (Anderson, 1991), the configural-cue model (Gluck & Bower, 1988b), and an extended version of the configural-cue model with dimensionalized, adaptive learning rate mechanisms. Although all of the models captured important qualitative aspects of the learning data, ALCOVE provided the best overall quantitative fit. The results suggest the need to incorporate some form of selective attention to dimensions in category-learning models based on stimulus generalization and cue conditioning.

Adult↗
PubMed1993

Hippocampal mediation of stimulus representation: a computational theory.

The authors propose a computational theory of the hippocampal region's function in mediating stimulus representations. The theory assumes that the hippocampal region develops new stimulus representations that enhance the discriminability of differentially predictive cues while compressing the representation of redundant cues. Other brain regions, including cerebral and cerebellar cortices, are presumed to use these hippocampal representations to recode their own stimulus representations. In the absence of an intact hippocampal region, the theory implies that other brain regions will attempt to learn associations using previously established fixed representations. Instantiated as a connectionist network model, the theory provides a simple and unified interpretation of the functional role of the hippocampal region in a wide range of conditioning paradigms, including stimulus discrimination, reversal learning, stimulus generalization, latent inhibition, sensory preconditioning, and contextual sensitivity. The theory makes novel predictions regarding the effects of hippocampal lesions on easy-hard transfer and compound preexposure. Several prior qualitative characterizations of hippocampal function--including stimulus selection, chunking, cue configuration, and contextual coding--are identified as task-specific special cases derivable from this more general theory. The theory suggests that a profitable direction for future empirical and theoretical research will be the study of learning tasks in which both intact and lesioned animals exhibit similar initial learning behaviors but differ on subsequent transfer and generalization tasks.

Animals↗
PubMed1988

From conditioning to category learning: an adaptive network model.

We used adaptive network theory to extend the Rescorla-Wagner (1972) least mean squares (LMS) model of associative learning to phenomena of human learning and judgment. In three experiments subjects learned to categorize hypothetical patients with particular symptom patterns as having certain diseases. When one disease is far more likely than another, the model predicts that subjects will substantially overestimate the diagnosticity of the more valid symptom for the rare disease. The results of Experiments 1 and 2 provide clear support for this prediction in contradistinction to predictions from probability matching, exemplar retrieval, or simple prototype learning models. Experiment 3 contrasted the adaptive network model with one predicting pattern-probability matching when patients always had four symptoms (chosen from four opponent pairs) rather than the presence or absence of each of four symptoms, as in Experiment 1. The results again support the Rescorla-Wagner LMS learning rule as embedded within an adaptive network model.

Association Learning↗
PubMedDate not supplied

Extending models of hippocampal function in animal conditioning to human amnesia.

Although most analyses of amnesia have focused on the loss of explicit declarative and episodic memories following hippocampal-region damage, considerable insights into amnesia can also be realised by studying hippocampal function in simple procedural, or habit-based, associative learning tasks. Although many simple forms of associative learning are unimpaired by hippocampal damage, more complex tasks which require sensitivity to unreinforced stimuli, configurations of multiple stimuli, or contextual information are impaired by hippocampal damage. In several recent papers we have developed a computational theory of hippocampal function which argues that this brain region plays a critical role in the formation of new stimulus representations during learning (Gluck & Myers, 1993, 1995; Myers & Gluck, 1996; Myers, Gluck, & Granger, 1995). We have applied this theory to a broad range of empirical data from studies of classical conditioning in both intact and hippocampal-lesioned animals, and the model correctly accounts for these data. The classical conditioning paradigm can be adapted for use in humans, and similar results for acquisition are obtained in both normal and hippocampal-damaged humans. More recently, we have begun to address an important set of category learning studies in both normals and hippocampal-damaged amnesics. This work integrates experimental studies of amnesic category learning (Knowlton, Squire, & Gluck, 1994) with theoretical accounts of associative learning, and builds on previously established behavioural correspondences between animal conditioning and human category learning (Gluck & Bower, 1988a). Our work to date illustrates some initial progress towards a more integrative understanding of hippocampal function in both animal and human learning, which may be useful in guiding further empirical and theoretical research in human memory and amnesia.

Amnesia↗