The neurobiology of learning and memory

The study of memory is a great challenge, perhaps the greatest in biological sciences. Memory involves changes in a tiny fraction of an extremely large pool of elements, a conclusion that makes the task of finding those changes using current technologies formidable. What can be done about this roadblock to neurological investigations of learning? One response that has become particularly productive in recent years is to study learning or learning-like phenomena in relatively simple "model" systems. The idea is to extract basic principles from these models in which molecular and anatomical details can be studied and then to use these in analyzing learning in higher regions of the brain. In this article we discuss current progress and emerging concepts derived from the simple system approach using animal models.     

The selective impairment of semantic memory

The selective impairment of semantic memory is described in three patients with diffuse cerebrallesions. These patients, selected on the basis of a failure to recognize or identify common objects (agnosia for objects), were investigated in detail. In particular, their perceptual, language and memory functions were assessed, and the limits and properties of their recognition difficulties explored.

It was found that knowledge of pictorial representations of objects, and of words, was impaired or impoverished, and in both instances knowledge of subordinate categories was more vulnerable than superordinate categories. Evidence is presented that this impairment of semantic memory cannot be accounted for by intellectual impairment, sensory or perceptual deficits, or expressive language disorder. The implications of damage to the semantic memory system for the operation of other cognitive systems, in particular short and long-term memory functions, are considered. Some tentative evidence for the structural basis for a hierarchically organized modality-specific semantic memory system is discussed.     

Investigating semantic memory impairments: The contribution of semantic priming

Abstract

The semantic priming task is a valuable tool in the investigation of semantic memory impairments in patients with acquired disorders of language. This is because priming performance reflects automatic or implicit access to semantic information, unlike most other tests of semantic knowledge, which rely on explicit, voluntary access. Priming results are important for two main reasons: First, normal priming results may be observed in patients who perform poorly on other semantic memory tests, enabling us to distinguish between loss of, or damage to, information in semantic memory, and voluntary access to that information. Second, we can investigate the detailed pattern of loss and preservation of different types of semantic information, by charting the priming effects for different kinds of words, and different kinds of semantic relations between primes and targets.

We discuss the use of the priming task in this context, and address some of the theoretical and methodological criticisms that have been raised in connection with use of the priming task to address these issues. We then describe two recent studies in which we have employed semantic priming tasks, along with other more traditional methods, to investigate specific questions about the semantic memory deficits of three patients.     

The neurobiology of fear memory reconsolidation and psychoanalytic theory

Advances in both experimental neuroscience and psychoanalytic theory and technique have made it possible to consider mechanisms by which psychodynamic psychotherapies might have an impact at the cellular and molecular level. Here potential analogies are drawn between (1) the mechanisms and results of blocking the reconsolidation of conditioned fear memories in the laboratory and (2) several key aspects of psychoanalytic process. A review of the biology of conditioned fear memory, including differences between extinction and inhibition of reconsolidation, indicates that this biology may have relevance to various ways in which psychoanalytic therapy is effective. The ideas proposed here might lead to further experimental attempts to understand the molecular biology of psychoanalysis.     

The contribution of autobiographical significance to semantic memory

We examined the importance of autobiographical significance (AS) in the representation and organization of semantic memory by examining which famous people are most likely to be associated with specific personal memories and whether or not this AS can be distinguished from other factors, such as familiarity. Norming studies with 45- to 55-year-old and 65- to 80-year-old participants suggested that AS is distinct from familiarity and that it interacts closely with emotional salience. Furthermore, in a set of experiments, we tested the hypothesis that AS is an important organizing principle in long-term episodic and semantic memory by contrasting performances on tests of recall, recognition, fame judgment, and speeded reading for famous names judged to be of either high or low personal relevance. Participants demonstrated a performance advantage (i.e., enhanced memory and faster responding) for autobiographically significant famous names, regardless of whether their own judgments or others' judgments were used to classify the names. The implications of these findings for models of semantic memory are discussed.     

Quantification and semantic memory

Two models are considered for how people verify explicitly quantified sentences, such as All fathers are parents and Some fathers are parents. The models share the same second stage, but have different first-stage mechanisms. In the Predicate Intersection Model, suggested by Meyer (1970), the first stage involves a serial, self-terminating search among names of categories that intersect the predicate category. In the Feature Comparison Model (Smith, Shoben & Rips, 1974a), the first stage involves evaluating the overall relatedness between the subject and predicate categories by comparing their semantic features. To test the models, three reaction time experiments required subjects to verify statements quantified by Some or All. In the first experiment, the semantic relatedness of categories in false Some-statements was varied. Contrary to predictions of the Predicate Intersection Model, related categories increased reaction time for both true and false Some-statements. While the first experiment revealed that All-statements took longer to verify than comparable Some-statements, the second experiment demonstrated that the All-Some difference can be eliminated by presenting both statement types in the same block of trials, also disconfirming the Predicate Intersection Model. Finally, Experiment III examined the meaning of Some-statements in more detail by having subjects interpret the quantifier Some as “some but not all.” With this interpretation, Some-statements took longer to verify than All-statements. Overall the results support the Feature Comparison Model.     

The structure of semantic person memory: evidence from semantic priming in person recognition

This paper reviews research on the structure of semantic person memory as examined with semantic priming. In this experimental paradigm, a familiarity decision on a target face or written name is usually faster when it is preceded by a related as compared to an unrelated prime. This effect has been shown to be relatively short lived and susceptible to interfering items. Moreover, semantic priming can cross stimulus domains, such that a written name can prime a target face and vice versa. However, it remains controversial whether representations of people are stored in associative networks based on co-occurrence, or in more abstract semantic categories. In line with prominent cognitive models of face recognition, which explain semantic priming by shared semantic information between prime and target, recent research demonstrated that priming could be obtained from purely categorically related, non-associated prime/target pairs. Although strategic processes, such as expectancy and retrospective matching likely contribute, there is also evidence for a non-strategic contribution to priming, presumably related to spreading activation. Finally, a semantic priming effect has been demonstrated in the N400 event-related potential (ERP) component, which may reflect facilitated access to semantic information. It is concluded that categorical relatedness is one organizing principle of semantic person memory.     

The deterioration of semantic memory in Alzheimer's disease.

Semantic memory impairment is a common feature of dementia of the Alzheimer type (DAT). Recent research has shown that patients with DAT are more impaired (relative to non-demented controls) in generating exemplars from a particular semantic category (e.g., animals) than words beginning with a particular letter, exhibit an altered temporal dynamic during the production of category exemplars, are impaired on confrontation naming tasks and make predominantly superordinate or semantically related errors, consistently misidentify the same objects across a variety of semantic tasks, and have alterations in multi-dimensional scaling models of their semantic network that are indicative of a loss of concepts and associations. These results are consistent with the view that Alzheimer's disease results in a breakdown in the organization and structure of semantic knowledge as neurodegeneration spreads to the association cortices that presumably store semantic representations.     

The role of short-term memory in semantic priming.

Two theories of priming were compared: spreading activation theories, in particular ACT, and compound-cue theories. Whereas ACT assumes that priming is a result of diffusing activation in long-term memory, compound-cue models suggest that priming results from a formation process of prime and target in short-term memory. Thirty-eight participants took part in a study that combined a digit span task with a double lexical decision task consisting of a prime and a target item. Digit span length (low, medium, and high) and prime type (related or unrelated word or nonword) were both within-subject variables. As expected, results showed significant priming effects. In favor of ACT, no interaction between digit span length and prime type was found. Additionally, a nonword inhibition effect (unrelated versus nonword prime) was found, which was predicted by compound-cue theories. This finding is discussed in terms of the process interference and response competition hypotheses.     

The effect of semantic context on prospective memory performance

The current study provides evidence for spontaneous processing in prospective memory (PM) or memory for intentions. Discrepancy-plus-search is the spontaneous processing of PM cues via disruptions in processing fluency of ongoing task items. We tested whether this mechanism can be demonstrated in an ongoing rating task with a dominant semantic context. Ongoing task items were manipulated such that the PM cues were members of a semantic category (i.e., Body Parts) that was congruent or discrepant with the dominant semantic category in the ongoing task. Results showed that participants correctly responded to more PM cues when there was a category discrepancy between the PM cues and ongoing task items. Moreover, participants' identification of PM cues was accompanied by faster ongoing task reaction times when PM cues were discrepant with ongoing task items than when they were congruent. These results suggest that a discrepancy-plus-search process supports PM retrieval in certain contexts, and that some discrepancy-plus-search mechanisms may result from the violation of processing expectations within a semantic context.     

Causal conditional reasoning and semantic memory retrieval: a test of the semantic memory framework

This study tested and refined a framework that proposes a mechanism for retrieving alternative causes and disabling conditions (Cummins, 1995) during reasoning. Experiment 1 examined the relation between different factors affecting retrieval. The test revealed high correlations between the number of possible alternative causes or disabling conditions and their strength of association and plausibility. Experiment 2 explored the hypothesis that due to a more extended search process, conditional inferences would last longer when many alternative causes or disabling conditions were available. Affirmation of the consequent (AC) and modus ponens (MP) latencies showed the hypothesized pattern. Denial of the antecedent (DA) and modus tollens (MT) inferences did not show latency effects. The experiment also identified an effect of the number of disabling conditions on AC and DA acceptance. Experiment 3 measured efficiency of disabler retrieval by a limited time, disabler generation task. As predicted, better disabler retrieval was related to lower acceptance of the MP and MT inferences.     

Cross-category structure in semantic memory

In Experiment I, subjects made similarity judgments about all 56 category terms listed in the Battig and Montague (1969) norms. These judgments were then subjected to a hierarchical clustering analysis. Experiment II demonstrated that the relations among the category labels are very similar to the relations among the high dominance exemplars of these categories. Experiment III showed that the distances between the category terms in the hierarchical clustering analysis could predict RTs in a same-different paradigm.     

Optimal foraging in semantic memory

Do humans search in memory using dynamic local-to-global search strategies similar to those that animals use to forage between patches in space? If so, do their dynamic memory search policies correspond to optimal foraging strategies seen for spatial foraging? Results from a number of fields suggest these possibilities, including the shared structure of the search problems-searching in patchy environments-and recent evidence supporting a domain-general cognitive search process. To investigate these questions directly, we asked participants to recover from memory as many animal names as they could in 3 min. Memory search was modeled over a representation of the semantic search space generated from the BEAGLE memory model of Jones and Mewhort (2007), via a search process similar to models of associative memory search (e.g., Raaijmakers & Shiffrin, 1981). We found evidence for local structure (i.e., patches) in memory search and patch depletion preceding dynamic local-to-global transitions between patches. Dynamic models also significantly outperformed nondynamic models. The timing of dynamic local-to-global transitions was consistent with optimal search policies in space, specifically the marginal value theorem (Charnov, 1976), and participants who were more consistent with this policy recalled more items.     

Bilingual retrieval from semantic memory

Bilinguals produced English and French words from two taxonomic categories. Analyses of outputs indicated they retrieved words by semantic category, but in clusters from the same language, half the subjects immediately translating the words retrieved. Translations aside, more shifts were across languages than across categories. Protocols also showed the same degree of semantic clustering and number of concepts retrieved as those of other bilinguals responding unilingually. The findings are consistent with separate lexicons for each language, tapping a common system of concepts. An alternative account is possible in terms of a single lexicon, organized along semantic lines, but with stronger links between words from the same language. This work was supported by a grant from the National Sciences and Engineering Research Council of Canada.     

FOK与情节记忆、语义记忆和内隐记忆关系的研究

实验采用R/K判断和PDP测量技术,研究了FOK判断与情节记忆、语义记忆和内隐记忆关系及其监测强度.实验结果表明FOK判断的准确性程度为R判断＞K判断,即对情节记忆监测的准确性要大于对语义记忆监测的准确性.FOK对于自动加工的预测准确性差异不显著,说明FOK监测对内隐记忆的作用是微弱的,由此推测无记忆是意识最高层面的活动.对记忆监测水平强度是由意识--无意识逐渐减弱的.FOK判断对意识性水平较高的记忆活动监测的准确性较强.     

The role of episodic and semantic memory in episodic foresight

In this paper we describe a special form of future thinking, termed “episodic foresight” and its relation with episodic and semantic memory. We outline the methodologies that have largely been developed in the last five years to assess this capacity in young children and non-human animals. Drawing on Tulving's definition of episodic and semantic memory, we provide a critical analysis of the role that both types of memory might have on the episodic foresight tasks described in the literature. We conclude by highlighting some unanswered questions and suggesting future directions for research that could further our understanding of how memory is intimately connected to episodic foresight.     

The influence of semantic relationships on older adult map memory

Research has shown that nonspatial features, including semantic categories, can bias younger adults' spatial location memory. For example, semantically related information is remembered as being closer in space than semantically unrelated information (Hirtle & Mascolo, 1986). These findings suggest that verbal information is concurrently encoded with spatial information and influences younger adults' spatial information retrieval. The present study explored whether older adults have a similar dependency between verbal and spatial information. In Experiment 1, older and younger adults learned maps depicting semantically categorizable landmarks. After learning, participants completed landmark free recall and distance estimation tasks. Younger adults recalled more landmarks from semantically organized maps compared with older adults. In addition, younger adults were more likely to underestimate the distance between semantically related landmarks than were older adults. Experiment 2 examined whether supportive instructions would influence older adults' use of verbal information when learning maps. When given instructions that encouraged semantic feature use, older adults remembered more landmarks, were more likely to cluster landmarks semantically, and demonstrated biases in distance estimation based on semantic relationships. These findings suggest that verbal influences on spatial/map learning in older adults depends on explicit instructions or environmental support at encoding. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

The interaction of semantic memory with storage and retrieval processes

A procedure for separating storage from retrieval (R. Chechile & D. L. Meyer, Journal of Mathematical Psychology, 1976, 14, 430–437) lead to the conclusion that memory development involves changes in both storage and retrieval. Nevertheless, these changes resulted from the interaction of storage and retrieval mechanisms with the age-related elaboration of the semantic memory system. This study shows that the memory improvement with age, between kindergarten and second grade, vanished when the meaningfulness of the materials were equated. The most plausible interpretation of the results is the hardware invariance hypothesis. According to that hypothesis, the memory apparatus for information processing is constant across ages, but the hardware is used more effectively if there is a better-developed semantic memory system.     

Information retrieval with semantic memory model

Psycholinguistic theories of semantic memory form the basis of understanding of natural language concepts. These theories are used here as an inspiration for implementing a computational model of semantic memory in the form of semantic network. Combining this network with a vector-based object-relation-feature value representation of concepts that includes also weights for confidence and support, allows for recognition of concepts by referring to their features, enabling a semantic search algorithm. This algorithm has been used for word games, in particular the 20-question game in which the program tries to guess a concept that a human player thinks about. The game facilitates lexical knowledge validation and acquisition through the interaction with humans via supervised dialog templates. The elementary linguistic competencies of the proposed model have been evaluated assessing how well it can represent the meaning of linguistic concepts. To study properties of information retrieval based on this type of semantic representation in contexts derived from on-going dialogs experiments in limited domains have been performed. Several similarity measures have been used to compare the completeness of knowledge retrieved automatically and corrected through active dialogs to a “golden standard”. Comparison of semantic search with human performance has been made in a series of 20-question games. On average results achieved by human players were better than those obtained by semantic search, but not by a wide margin.