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.     

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.     

Alcoholic Korsakoff patients' retrieval from semantic memory

Alcoholic Korsakoff patients' rate of retrieval from semantic memory was investigated. It was found that their rate of retrieval from “lexical” semantic memory was nearly normal, but their rate of retrieval from “conceptual” semantic memory was impaired. In addition, an attempt to “prime” their lexical semantic memory by requesting the same category to be searched on adjacent trials met with failure. It was concluded that Korsakoff patients' lexical storage is probably organized normally, but their conceptual organization is not. Parallels with these patients' episodic memory impairments are discussed and possible interactions between episodic and semantic memory are proposed.     

Fuzziness in semantic memory: Choosing exemplars of subjective categories

Class membership is a fundamental relationship between concepts in semantic memory. Recent research indicates that, class membership may subjectively be a continuous type of relationship. The processing of information about the degree to which items belong to a particular class was investigated in an experiment in which subjects compared two statements describing class membership relationships. The results strongly supported a simple model which describes the judgment process as directly involving subjective degree-of-truthfulness values. The success of the model indicates that the subjects were able to process this kind of fuzzy information in a consistent and systematic manner. Some of the implications of the human competancy for processing fuzzy information are discussed.     

Individual differences in speed of retrieval from semantic memory

In the first of two experiments, the stimulus items consisted of category names followed by a single letter (e.g., fruit-P). The subjects (half introverted, half extraverted) were required to respond as quickly as possible with a member of the specified category starting with the letter. Extraverts responded significantly faster than introverts, and more so when the most likely response was of low frequency than when it was of high frequency. In the second experiment, subjects were assigned to one of four groups representing the four combinations of high and low Extraversion and high and low General Activation. The speed-of-recall task from the first experiment was used on some trials; on the remaining trials, a speed-of-recognition task was used. Extraverts had greater response speed than introverts for recall, but not for recognition. That finding, plus interactions between Extraversion and General Activation, suggested an interpretation of the results in terms of the Yerkes-Dodson Law.     

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.     

Associative strength level and retrieval inhibition in semantic memory

In a series of investigations, E. F. Loftus (1973; G. R. Loftus & E. F. Loftus, 1974; E. F. Loftus, Senders, & Turkletaub, 1974) discovered that the latency of item retrieval from a semantic category was reduced if it immediately followed an earlier retrieval from the same category, a phenomenon attributed to spreading activation. Subsequently, Brown (1981) discovered an increase in latency across extended retrievals from a single semantic category. The present investigation followed up this finding by comparing exemplars that varied in strength of association to the category name. The probability of obtaining inhibition (longer latencies and increased errors) was inversely related to the associative strength of the exemplars. The results suggest that low-strength category associates build up inhibition more rapidly because they accrue situational strength relatively more rapidly than high-strength associates.     

Evidence for parallel semantic memory retrieval in dual tasks

In this dual-task study, we applied both cross-talk logic and locus-of-slack logic to test whether participants can retrieve semantic categories in Task 2 in parallel to Task 1 bottleneck processing. Whereas cross-talk logic can detect parallel memory retrieval only in conditions of categorical overlap between tasks, the locus-of-slack approach is independent of such restrictions. As was expected, using the cross-talk logic, we found clear evidence for parallel retrieval of semantic categories when there was categorical overlap between tasks (Experiment 1). Locus-of-slack-based evidence for parallel semantic retrieval was found, however, both in conditions with (Experiment 1) and in those without (Experiment 2) categorical overlap between tasks. Crucially,however, increasing the demand for resources required to switch from Task 1 to Task 2 eliminated even the locus-of-slack-based evidence for parallel memory retrieval during the psychological refractory period (Experiment 3). Together, our results suggest that parallel retrieval is not bound to conditions of categorical overlap between tasks but, instead, is contingent upon resources needed for switching between tasks (e.g., Oriet, Tombu, & Jolicoeur, 2005).     

Evidence for the contribution of a threshold retrieval process to semantic memory

It is widely held that episodic retrieval can recruit two processes: a threshold context retrieval process (recollection) and a continuous signal strength process (familiarity). Conversely the processes recruited during semantic retrieval are less well specified. We developed a semantic task analogous to single-item episodic recognition to interrogate semantic recognition receiver-operating characteristics (ROCs) for a marker of a threshold retrieval process. We fitted observed ROC points to three signal detection models: two models typically used in episodic recognition (unequal variance and dual-process signal detection models) and a novel dual-process recollect-to-reject (DP-RR) signal detection model that allows a threshold recollection process to aid both target identification and lure rejection. Given the nature of most semantic questions, we anticipated the DP-RR model would best fit the semantic task data. Experiment 1 (506 participants) provided evidence for a threshold retrieval process in semantic memory, with overall best fits to the DP-RR model. Experiment 2 (316 participants) found within-subjects estimates of episodic and semantic threshold retrieval to be uncorrelated. Our findings add weight to the proposal that semantic and episodic memory are served by similar dual-process retrieval systems, though the relationship between the two threshold processes needs to be more fully elucidated.     

Distinguishing the neural correlates of episodic memory encoding and semantic memory retrieval

Episodic memory and semantic memory interact very closely. In particular, episodic memory encoding (EE) tends to elicit semantic memory retrieval (SR), and vice versa. Thus, similar activations for EE and SR in functional neuroimaging studies may reflect shared memory processes, or they may reflect the fact that EE and SR are usually confounded. To address this issue, we used a factorial functional magnetic resonance imaging approach to disentangle the neural correlates of EE and SR. Within the left temporal lobe, the hippocampus was associated with successful EE, whereas a posterior lateral region was associated with successful SR. Within the left inferior prefrontal cortex, a posterior region was involved in SR, a mid region was involved in both SR and EE, and an anterior region was involved in EE, but only when SR was also high. Thus, the neural correlates of EE and SR are dissociable but interact in specific brain regions.     

Contributions of category and fine-grained information to location memory: When categories don't weigh in

Several studies have shown that people's memory for location can be influenced by categorical information. According to a model proposed by Huttenlocher, Hedges, and Duncan (1991), people estimate location by combining fine-grained item-level information in memory with category-level information. When the fine-grained information is inexact, category-level information is given greater weight, which leads to biased responses. We manipulated the distribution of locations presented in order to alter the usefulness of category information, and we manipulated background texture in order to alter accuracy of fine-grained memory. The distributional information reduced bias without altering overall accuracy of responding, whereas the background texture manipulation affected accuracy without changing bias. Our results suggest that category information may weigh in only when it is actively processed.     

Midazolam amnesia and retrieval from semantic memory: Developing methods to test theories of implicit memory

Studies of organic anterograde amnesia have been central to the development of theories of implicit memory. Pharmacological amnesia provides an additional method for exploring implicit memory, allowing for the experimental manipulation of amnesia and the testing of more participants. A significant concern with pharmacological amnesia is whether its cognitive effects are specific to explicit memory. The current research examines the effects of the benzodiazepine, midazolam, on retrieval from semantic memory and encoding in explicit memory. We focus on midazolam because it holds significant advantages over other benzodiazepines in inducing pharmacological amnesia and prior research suggests it may be useful for testing theories of implicit memory. Our results demonstrate that midazolam does not impair accuracy of retrieval from semantic categories, even when it produces anterograde amnesia for retrieved category items on a later recall test. These results suggest ways midazolam can be used to help test theories of implicit memory.     

Contributions of the medial temporal lobe to declarative memory retrieval: manipulating the amount of contextual retrieval

We investigated how the hippocampus and its adjacent mediotemporal structures contribute to contextual and noncontextual declarative memory retrieval by manipulating the amount of contextual information across two levels of the same contextual dimension in a source memory task. A first analysis identified medial temporal lobe (MTL) substructures mediating either contextual or noncontextual retrieval. A linearly weighted analysis elucidated which MTL substructures show a gradually increasing neural activity, depending on the amount of contextual information retrieved. A hippocampal engagement was found during both levels of source memory but not during item memory retrieval. The anterior MTL including the perirhinal cortex was only engaged during item memory retrieval by an activity decrease. Only the posterior parahippocampal cortex showed an activation increasing with the amount of contextual information retrieved. If one assumes a roughly linear relationship between the blood-oxygenation level-dependent (BOLD) signal and the associated cognitive process, our results suggest that the posterior parahippocampal cortex is involved in contextual retrieval on the basis of memory strength while the hippocampus processes representations of item-context binding. The anterior MTL including perirhinal cortex seems to be particularly engaged in familiarity-based item recognition. If one assumes departure from linearity, however, our results can also be explained by one-dimensional modulation of memory strength.     

Beyond HERA: Contributions of specific prefrontal brain areas to long-term memory retrieval

Recent neuroimaging studies have provided a wealth of information about areas within prefrontal cortex involved in long-term memory. These studies prompted a proposal by Tulving and colleagues (Tulving, Kapur, Craik, Habib, & Houle, 1994) that prefrontal contributions to memory function are related to laterality differences (the hemispheric encoding/retrieval asymmetry model). This review goes beyond a general characterization of prefrontal lobes to a more specific analysis of distinct areas within the prefrontal cortex. Separate prefrontal areas, sometimes within the same hemisphere, are discussed in terms of selective contributions that they might make to memory retrieval. In the end, it is concluded that a framework which tries to understand prefrontal function in terms of specific areas is a useful complement to models, like HERA, which attempt to find unifying principles across multiple areas.     

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.     

Category similarity effects in children's semantic memory retrieval

Fourth-, sixth-, and eighth-grade students were required to indicate whether or not a stimulus word belonged in either of two semantic categories that were held in memory. Each category pair was either semantically similar or semantically dissimilar. The results indicated that even for the youngest children, similar categories required less search time than dissimilar categories. It was suggested that while dissimilar categories had to be accessed successively prior to search, subjects were able to consolidate similar categories into a superordinate group which eliminated the time to shift from one category to another during search. The results were contrasted with clustering studies which have demonstrated a minimal amount of memory facilitation in children for conceptually related items over unrelated items.     

Dual-task influences on retrieval from semantic memory and coordination dynamics

Bimanual 1:1 rhythmic coordination was performed while retrieving words from a specified category. The effects of divided attention (DA) on coordination were indexed by changes in mean relative phase and recurrence measures of shared activity between the two limbs. Effects of DA on memory were indexed by deficits in exemplars retrieved relative to the baseline. Shifts in relative phase were found, accompanied by a recall deficit for DA during the retrieval task. DA also reduced the degree of shared activity between left and right rhythmic motions. Our discussion focuses on DA-induced parameter changes in retrieval and coordination dynamics, as well as on the hypothesis that stability is the general factor mediating dual-task performance.     

Aging and autobiographical memory: dissociating episodic from semantic retrieval

Cognitive aging research documents reduced access to contextually specific episodic details inolder adults, whereas access to semantic or other nonepisodic information is preserved or facilitated. The present study extended this finding to autobiographical memory by using a new measure; the Autobiographical Interview. Younger and older adults recalled events from 5 life periods. Protocols were scored according to a reliable system for categorizing episodic and nonepisodic information. Whereas younger adults were biased toward episodic details reflecting happenings, locations, perceptions, and thoughts, older adults favored semantic details not connected to a particular time and place. This pattern persisted after additional structured probing for contextual details. The Autobiographical Interview is a useful instrument for quantifying episodic and semantic contributions to personal remote memory.