Retrieval from semantic memory and its implications for Alzheimer's disease.

In 3 experiments, participants generated category exemplars (e.g., kinds of fruits) while a voice key and computer recorded each response latency relative to the onset of responding. In Experiment 1, mean response latency was faster when participants generated exemplars from smaller categories, suggesting that smaller mental search sets result in faster mean latencies. In Experiment 2, a concurrent secondary task increased mean response latency, suggesting that slowed mental processing results in slower mean latencies. In Experiment 3, the mean response latency of Alzheimer's participants was faster than that of elderly controls, which is consistent with the idea that the semantic memory impairments of Alzheimer's disease patients stem primarily from a reduction in available items (as in Experiment 1) rather than retrieval slowing (as in Experiment 2). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory facilitation following the administration of the benzodiazepine triazolam.

The benzodiazepine, triazolam, facilitates the retrieval from memory of information presented just before the administration of this drug at doses that impair explicit recall of information presented and remembered after drug administration. This effect was apparent for recall of unrelated words (Experiment 1) as well as highly related stimuli (category exemplars, Experiment 2). Normal volunteers were administered placebo and 4.6 and 6.0 μg/kg of triazolam (Experiment 1) and placebo, 0.258, 0.375, and 0.500 mg of triazolam (Experiment 2) using double-blind crossover designs. The observed effect is interpreted as due to changes in how information is retrieved from memory rather than as a result of either blockage of interference effects or alterations in processes involved in memory consolidation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrieval dynamics in recognition and list discrimination: further evidence of separate processes of familiarity and recall

Two experiments tested the hypothesis that the time course of retrieval from memory is different for familiarity and recall. The response-signal method was used to compare memory retrieval dynamics in yes-no recognition memory, as a measure of familiarity, with those of list discrimination, as a measure of contextual recall. Responses were always made with regard to membership in two previous study lists. In Experiment 1 an exclusion task requiring positive responses to words from one list and negative responses to new words and words from the nontarget list was used. In Experiment 2, recognition and list discrimination were separate tasks. Retrieval curves from both experiments were consistent, showing that the minimal retrieval time for recognition was about 100 msec faster than that for list discrimination. Repetition affected asymptotic performance but had no reliable effects on retrieval dynamics in either the recognition or the list-discrimination task.     

Relational similarity and context effects in category verification.

Two experiments with a total of 50 undergraduate and graduate students measured the effects of coordinate falses, which pair 2 exemplars from a common category (e.g., "A dog is a cat"), on latencies to true items in a category verification task. Results show that although, relative to anomalous falses, coordinate falses did not increase latencies to trues, the size of the increase did not vary with the similarity of the coordinates. Furthermore, latencies were faster to coordinate falses that were more similar than to coordinate falses that were less similar. These results suggest relational similarity is as powerful a predictor of performance in category verification as is attribute similarity. Finally, there was some evidence that the increase in latencies was the same for typical and atypical category exemplars. It is concluded that this last finding, if substantiated, indicates that relational information is generally accessed prior to attribute information. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

By land or by sea: The role of perceptual similarity in infants' categorization of animals.

In 3 experiments, the authors used an object-examining task to investigate the role of perceptual similarity in infants' categorization. In Experiment 1, infants were familiarized with a set of either perceptually similar or perceptually variable exemplars from 1 category and tested with novel exemplars from both categories. Ten-month-olds did not respond to the category in either condition, and 13-month-olds responded categorically in both conditions but somewhat differently in the 2 conditions. Experiment 2 showed that when 10-month-olds were familiarized with similar exemplars but not with variable exemplars, they responded to the categorical distinction when given tests with typical exemplars. Experiment 3 established that 10-month-olds could differentiate among the exemplars. These results suggest that the perceptual similarity of the exemplars influences infants' recognition of categorical distinctions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Available but unattended conceptual information in working memory: Temporarily active semantic content or persistent memory for prior operations?

In 2 experiments, the authors investigated available but unattended information following working memory task demands. The experimental task presented a memory set containing exemplars from 2 conceptual categories. Following instructions to focus attention on only 1 category, priming of both categories was assessed with category comparisons of exemplar pairs. Priming was greatest for the focused category and for exemplars from the memory set (direct priming). Priming also extended to new exemplars of both categories (indirect priming) and showed little decline over more than 1 min of intervening processes. Finally, changing between category exemplars and features across memory set and comparison phases eliminated the indirect priming. These results support a persistent, operation-specific, procedural account of available but unattended conceptual information in working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Storage and retrieval of associative clusters: A stages-of-learning analysis of associative memory traces.

In this research, the assumptions underlying the unitary trace theory of item representation and acquisition were tested in two cued-recall experiments in which the degree of preexperimental knowledge (typicality) was manipulated. Subjects learned lists of word triads (each of which consisted of a single cue and two targets) to a stringent acquisition criterion. In Experiment 1, typicality was manipulated in the absence of semantic relationships between members of the associative clusters. In Experiment 2, semantic relationships were present among cluster members, and preexperimental knowledge was manipulated by varying the degree of intracluster category membership as measured by whether cue and target items were typical or atypical category exemplars. In both experiments a mathematical model that embodies stages-of-learning distinctions was used to analyze the acquisition data. The results indicated that (1) cues and targets were represented in a single holistic memory trace, and (2) the manipulation of the degree of preexperimental knowledge affected both trace storage and retrieval learning, but had only a minimal impact on retrieval performance between the time a trace was stored and the time retrieval learning was complete. It was argued that these findings are consistent with a single unitary trace interpretation, namely, the modified storage-retrieval model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory storage and retrieval processes in category learning.

Studied the detailed course of learning for categorization tasks defined by independent or contingent probability distributions over the features of category exemplars in 2 experiments with 72 college-age Ss. Ss viewed sequences of bar charts that simulated symptom patterns and responded to each chart with a recognition and a categorization judgment. Fuzzy, probabilistically defined categories were learned relatively rapidly when individual features were correlated with category assignment, more slowly when only patterns carried category information. Limits of performance were suboptimal, evidently because of capacity limitations on judgmental processes as well as limitations on memory. Categorization proved systematically related to feature and exemplar probabilities, under different circumstances, and to similarity among exemplars of categories. Unique retrieval cues for exemplar patterns facilitated recognition but entered into categorization only at retention intervals within the range of short-term memory. Findings are interpreted within the framework of a general array model that yields both exemplar-similarity and feature-frequency models as special cases and provides quantitative accounts of the course of learning in each of the categorization tasks studied. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel memory retrieval in dual-task situations: I. Semantic memory.

Can participants retrieve information about the 2nd of 2 stimuli while they are processing the 1st? Four experiments suggest they can. Reaction times to the 1st stimulus were faster if it came from the same category as the 2nd than if it came from a different category. This category-match effect was observed for letter-digit discrimination (Experiment 1), magnitude and parity judgments about digits (Experiment 2), and lexical decisions (Experiment 3). Experiment 4 showed that the 2nd stimulus could semantically prime the 1st. The category-match effect was observed only when the same task was performed on the 2 stimuli. When the task changed from the Ist stimulus to the 2nd, there was no advantage of a category match. This dependence on task set may explain previous failures to find parallel retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel memory retrieval in dual-task situations: II. Episodic memory.

Three experiments asked whether subjects could retrieve information from a 2nd stimulus while they retrieved information from a 1st stimulus. Ss performed recognition judgments on each of 2 words that followed each other by 0, 250, and 1,000 msec (Experiment 1) or 0 and 300 msec (Experiments 2 and 3). In each experiment, reaction time to both stimuli was faster when the 2 stimuli were both targets (on the study list) or both lures (not on the study list) than when 1 was a target and the other was a lure. Each experiment found priming from the 2nd stimulus to the lst when both stimuli were targets. Reaction time to the 1st stimulus was faster when the 2 targets came from the same memory structure at study (columns in Experiment l; pairs in Experiment 2; sentences in Experiment 3) than when they came from different structures. This priming is inconsistent with discrete serial retrieval and consistent with parallel retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recognition memory for new associations: electrophysiological evidence for the role of recollection

The electrophysiological correlates of recognition memory for new associations were investigated in two experiments. In both experiments subjects first studied unrelated word pairs. At test, they were presented with old words in the same pairing as at study (same pairs), old words in a different pairing from study (rearranged pairs), and pairs of new words. In Experiment 1 the test requirement was to discriminate between old and new pairs and, for any pair judged old, to then judge whether the pair was the same or rearranged. In Experiment 2 the requirement was merely to discriminate between old and new pairs. Event-related potentials (ERPs) were recorded for correctly classified same, rearranged and new pairs. The ERPs elicited by same pairs exhibited a similar pattern of effects in both experiments. Relative to the ERPs to new pairs, these effects took the form of sustained positive shifts with two distinct scalp maxima, over the left temporo-parietal and right frontal scalp respectively. ERPs to rearranged pairs showed effects which were similar in scalp topography, but markedly smaller in magnitude. This pattern of ERP effects closely resembles that found previously for test items defined as recollected on the basis of their attracting a successful source judgement. The findings therefore suggest that associative recognition memory shares some of the recollective processes that are engaged by the requirement to retrieve contextual information about a study episode. The findings from Experiment 2 indicate that the processes associated with the recollection of associated pairs are engaged regardless of whether the retrieval of associative information is an explicit task requirement.     

Activation of exemplars in the process of assessing social category attitudes.

Three experiments used process measures of concept activation to provide evidence—consistent with previous research, which had used only outcome and self-report measures—that people use category exemplars to assess their social category attitudes. The studies were based on the well-established principle that individuals selectively activate different aspects of their knowledge about a topic, depending on which aspect is relevant for a specific judgment. Exemplar activation was measured through ambiguous anagrams (Experiment 1), word fragment completions (Experiment 2), and response latencies (Experiment 3). In each case, exemplar activation was greater when participants had recently judged their attitudes toward a social category than when they had recently judged a definition of the category. Implications for theories of attitude change and attitude-behavior consistency are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorization of speech by infants: Support for speech-sound prototypes.

This study tested 6-month-old infants' categorization of speech stimuli to investigate whether infants organize speech categories around "prototypes." In Experiment 1, infants first discriminated single "good" exemplars from two different vowel categories. They were then tested with 64 novel exemplars, 32 from each vowel category. The test stimuli varied in the degree to which they conformed to adult-defined prototypes of the two categories. The results showed that infants correctly sorted the novel stimuli over 90% of the time. In Experiment 2, we trained two groups of infants, one with a good (prototypical) exemplar from a vowel category and the other with a poor (nonprototypical) exemplar. Then we tested both groups with 16 novel exemplars from that same vowel category. Generalization to novel members of the category was significantly greater following exposure to the prototypical exemplar. Results are consistent with a model of speech perception that holds that young human infants organize vowel categories around prototypes. This may contribute to their seemingly efficient processing of speech information, even in the first half year of life. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of the Contents of Working Memory--A Comparison of Two Paradigms and Two Age Groups.

Two experiments investigated whether young and old adults can temporarily remove information from a capacity-limited central component of working memory (WM) into another component, the activated part of long-term memory (LTM). Experiment 1 used a modified Sternberg recognition task (S. Sternberg, 1969); Experiment 2 used an arithmetic memory-updating task. In both paradigms, participants memorized 2 lists, one of which was cued as temporarily irrelevant. Removal of the irrelevant list from capacity-limited WM was indexed by the disappearance of list-length effects of that list on latencies for concurrent processing tasks. Young adults could outsource the irrelevant list within 2-3 s and retrieve it back into the central part of WM later. Old adults showed the same flexibility in the arithmetic updating task but seemed somewhat less able or inclined to temporarily move information into the activated part of LTM in the modified Sternberg task. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Conceptual distinctiveness supports detailed visual long-term memory for real-world objects.

Humans have a massive capacity to store detailed information in visual long-term memory. The present studies explored the fidelity of these visual long-term memory representations and examined how conceptual and perceptual features of object categories support this capacity. Observers viewed 2,800 object images with a different number of exemplars presented from each category. At test, observers indicated which of 2 exemplars they had previously studied. Memory performance was high and remained quite high (82% accuracy) with 16 exemplars from a category in memory, demonstrating a large memory capacity for object exemplars. However, memory performance decreased as more exemplars were held in memory, implying systematic categorical interference. Object categories with conceptually distinctive exemplars showed less interference in memory as the number of exemplars increased. Interference in memory was not predicted by the perceptual distinctiveness of exemplars from an object category, though these perceptual measures predicted visual search rates for an object target among exemplars. These data provide evidence that observers' capacity to remember visual information in long-term memory depends more on conceptual structure than perceptual distinctiveness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The disparate effects of Alzheimer's disease and Huntington's disease on semantic memory.

Alzheimer's disease (AD) and Huntington's disease (HD) impair performance on semantic memory tasks, but researchers disagree on whether AD and HD cause these impairments in the same manner. According to one view, AD disrupts the storage of semantic memories, whereas HD disrupts the retrieval of semantic memories. Dissenters argue that AD, like HD, disrupts retrieval. In this study, participants generated category exemplars (e.g., kinds of fruits) for 1 min, and response latencies were examined. Relative to healthy controls, the 12 AD patients produced a larger proportion of responses earlier in the recall period, consistent with the view that AD patients quickly exhaust their limited supply of items in storage. By contrast, the 12 HD patients produced a larger proportion of their responses late in the recall period, consistent with the view that HD slows retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional limits in memory retrieval.

The hypothesis that episodic memory retrieval can occur in parallel with other cognitive processes was tested in 2 experiments. Participants memorized words and then performed speeded cued recall (Experiment 1) or speeded yes-no recognition (Experiment 2) in a dual-task situation. The psychological refractory period design was used: The participant was presented with a single test item at various stimulus onset asynchronies (SOAs; 50-1,000 ms) after a tone was presented in an auditory-manual 2-alternative choice reaction task. Reducing the SOA increased the memory task reaction times. This slowing was additive with the effect of variables slowing retrieval in the memory task. The results indicate that memory retrieval is delayed by central processes in the choice task, arguing that the central bottleneck responsible for dual-task interference encompasses memory retrieval as well as response selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Big" versus "little" science: comparative analysis of program projects and individual research grants

The verbal fluency task requires generation of category exemplars and appears to be an example of what M. Moscovitch (1995) calls a strategic test of memory retrieval. Four experiments explored the role of individual differences in working memory (WM) capacity on verbal fluency under various secondary load conditions. High WM participants consistently recalled more exemplars. However, load conditions caused a decline in recall only for high WM participants. Low WM participants showed no effect of secondary workload on exemplar generation. WM group differences and load effects were observed even in the 1st min of retrieval, which suggests that differences were not due to differences in knowledge. A model of retrieval is supported that relies on cue-based-automatic activation, monitoring of output for errors, controlled suppression of previously recalled items, and controlled strategic search.     

The role of working memory capacity in retrieval.

The verbal fluency task that requires generation of category exemplars and appears to be an example of what M. Moscovitch (1995) calls a strategic test of memory retrieval. Four experiments explored the role of individual differences in working memory (WM) capacity on verbal fluency under various secondary load conditions. High WM participants consistently recalled more exemplars. However, load conditions caused a decline in recall only for high WM participants. Low WM participants showed no effect of secondary workload on exemplar generation. WM group differences and load effects were observed even in the 1st min of retrieval, which suggests that differences were not due to differences in knowledge. A model of retrieval is supported that relies on cue-based-automatic activation, monitoring of output for errors, controlled suppression of previously recalled items, and controlled strategic search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)