Category and letter fluency in semantic dementia, primary progressive aphasia, and Alzheimer's disease

This study examined the impact of various degenerative dementias on access to semantic knowledge and the status of semantic representations. Patients with semantic dementia, primary progressive aphasia, and Alzheimer's disease were compared with elderly controls on tasks of category and letter fluency, with number of words generated, mean lexical frequency and errors recorded. The findings are consistent with the view that category and letter fluency rely on both common and unique cognitive processes. Fluency tasks, with the richness of data obtained, are valuable in distinguishing different dementia syndromes from one another.     

Differential impacts of age of acquisition on letter and semantic fluency in Alzheimer's disease patients and healthy older adults

The degree to which the typical age of acquisition (AoA) of words and word frequency have separable influences on verbal production tasks has been strongly debated. To examine the overlap between these factors in verbal fluency tasks, the performance of Alzheimer's disease (AD) patients (N?=?34) and normal elderly controls (N?=?36) was compared on semantic (e.g., vegetables) and letter (e.g., words that begin with F) fluency tasks. These comparisons revealed that words generated for the semantic fluency task had an earlier AoA while words generated for the letter fluency task had a higher word frequency. Differences in AoA between AD patients and controls were larger for semantic than letter fluency. These results suggest that AoA has an effect on verbal production that is independent of word frequency and that AoA has a semantic locus.     

Differential impacts of age of acquisition on letter and semantic fluency in Alzheimer's disease patients and healthy older adults

The degree to which the typical age of acquisition (AoA) of words and word frequency have separable influences on verbal production tasks has been strongly debated. To examine the overlap between these factors in verbal fluency tasks, the performance of Alzheimer's disease (AD) patients (N = 34) and normal elderly controls (N = 36) was compared on semantic (e.g., vegetables) and letter (e.g., words that begin with F) fluency tasks. These comparisons revealed that words generated for the semantic fluency task had an earlier AoA while words generated for the letter fluency task had a higher word frequency. Differences in AoA between AD patients and controls were larger for semantic than letter fluency. These results suggest that AoA has an effect on verbal production that is independent of word frequency and that AoA has a semantic locus.     

Category size effects revisited: frequency and masked priming effects in semantic categorization

Previous work indicates that semantic categorization decisions for nonexemplars (e.g., deciding that TURBAN is not an animal name) are faster for high-frequency words than low-frequency words. However, there is evidence that this result might depend on category size. When narrow categories are used (e.g., Months, Numbers), there is no frequency effect for nonexemplars. This result is confirmed, and is explained in terms of a category search model, which allows a "No" decision to be generated without access to the lexical entry for the target word. This explains the absence of a frequency effect, but not the presence of a strong masked repetition priming effect, which is assumed to have a lexical source. It is shown that this effect may not be lexical, since nonwords also show similar priming. Both of these priming effects disappear when a larger category is used. This pattern of results is explained on the assumption that category search is only possible with small categories, and that tentative category decisions are generated for the unconsciously perceived prime, which leads to a marked response congruence effect.     

Shared lesion correlates of semantic and letter fluency in post-stroke aphasia

Lesion–symptom mapping studies have reported a temporal versus frontal dissociation between semantic and letter fluency, and mixed evidence regarding the role of white matter. Mass-univariate and multivariate lesion–symptom mapping was used to identify regions associated with semantic and letter fluency deficits in post-stroke aphasia. Multivariate LSM revealed broad networks including underlying white matter, and substantial overlap between both types of fluency, suggesting that semantic fluency and letter fluency largely rely on the same neural system. All data are available on OSF.     

Lexical and semantic fluency discrepancy scores in aMCI and early Alzheimer's disease

Episodic memory is compromised in amnestic mild cognitive impairment (aMCI), but lesser deficits in other cognitive domains are also commonly observed and may be helpful in identifying this group. The relative difference in performance on lexical and semantic fluency tasks may be a sensitive and specific measure in aMCI and early Alzheimer's disease (AD). We compared four groups of participants, 35 early AD, 47 aMCI, 24 healthy controls, and 18 depressive out‐patient controls, on semantic and lexical fluency as well as other neuropsychological tests. Early AD and aMCI patients showed a distinct pattern of semantic impairment in the two fluency measures compared with the healthy and depressive controls. The findings implicate early failure of the semantic memory system in aMCI and AD and suggest that consideration of the discrepancy in performance on semantic and lexical fluency measures may help in the early identification of AD.     

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.     

Category width and differentiation in semantic categories

The hypothesis that the judgemental categorizing behaviour measured by Pettigrew's Category-Width scale is linked to semantic categorization is investigated. Individual differences in broad vs. narrow categorizing behaviour measured by the C-W scale are reconceptualized within the framework of Rosch's (1977) theory of human categorization. Two extreme groups on the C-W scale, broad categorizers and narrow categorizers, were selected as subjects. One experiment employed a short-term release-from-proactive-inhibition paradigm. The amount of discrepancy in recall between the preshift and the shift trials was used as an index to perceived semantic distance. The result showed that narrow categorizers perceived the same fuzzy items in a semantic category as less similar to the good exemplars of that category than broad categorizers did. In a further experiment using a semantic-categorization technique, narrow categorizers judged the same fuzzy items as category members less frequently than broad categorizers did, indicating that narrow categorizers possess more differentiated semantic categories than do broad categorizers. These findings are seen as an extension of the differential categorizing behaviour on artificial categories in the C-W scale to semantic categorization for which there is a pre-existing system.     

Use of semantic context by patients with Alzheimer's disease

In this study we used semantic-priming procedures to examine limitations in the use of semantic context by patients with Alzheimer's disease. We also tried to determine whether any such contextual effects were mediated solely through automatic processes or whether attentional processes were also involved. Three tasks were applied to examine the effect of semantic context on the performance of 18 normal elderly and 18 normal young subjects, and on 18 patients with Alzheimer's disease. When normal and demented subjects were asked to decide whether a given item was a member of a certain category, results showed that their response times were equally affected by the item's dominance in the category. The time that demented patients took to recognize a word was actually affected more by the semantic context provided by a priming sentence than was that of normal subjects. When asked to generate the final word of an incomplete sentence, demented subjects performed very poorly unless potential responses were highly constrained by sentence context.     

Category and Attribute Knowledge Deterioration in Alzheimer's Disease

A prevalent theory regarding the deterioration of semantic memory in Alzheimer's disease is that it is a bottom-up process. If this is true, performance on tests of attribute knowledge should decline more rapidly than performance on tests of categorical knowledge as dementia severity increases. In the present study, a convincing pattern of findings to either support or reject the theory failed to emerge. This raised questions regarding the ability to separate attribute and categorical knowledge, and whether one can be tested without influence of the other. Questions also were raised regarding the additional cognitive processes needed to complete tasks of semantic memory.     

Masked priming effects in semantic categorization are independent of category size

The question whether subliminal primes can activate their semantic meaning or not is still of interest today. Three different competing theories have tried to account for the often inconsistent research results: The semantic categorization hypothesis, the direct motor specification hypothesis, and the category search model. The present study aimed to shed light on these different points of view by examining the role of category size in response congruency effects when novel primes are used. Three experiments were conducted and a transparent pattern of results emerged: Significant priming effects were obtained across different tasks, irrespective of category size and irrespective of stimulus set size. The findings are discussed in terms of the three theoretical frameworks. It becomes clear that the present results provide strong evidence in favor of the semantic categorization hypothesis, which assumes semantic processing of subliminal primes.     

The semantic organization of the animal category: evidence from semantic verbal fluency and network theory

Semantic memory is the subsystem of human memory that stores knowledge of concepts or meanings, as opposed to life-specific experiences. How humans organize semantic information remains poorly understood. In an effort to better understand this issue, we conducted a verbal fluency experiment on 200 participants with the aim of inferring and representing the conceptual storage structure of the natural category of animals as a network. This was done by formulating a statistical framework for co-occurring concepts that aims to infer significant concept-concept associations and represent them as a graph. The resulting network was analyzed and enriched by means of a missing links recovery criterion based on modularity. Both network models were compared to a thresholded co-occurrence approach. They were evaluated using a random subset of verbal fluency tests and comparing the network outcomes (linked pairs are clustering transitions and disconnected pairs are switching transitions) to the outcomes of two expert human raters. Results show that the network models proposed in this study overcome a thresholded co-occurrence approach, and their outcomes are in high agreement with human evaluations. Finally, the interplay between conceptual structure and retrieval mechanisms is discussed.     

Priming and semantic memory loss in Alzheimer's disease

Semantic memory (SM) was investigated in six patients with probable Alzheimer's disease (AD) by on-line measurement of semantic priming in a lexical decision task, and off-line tests of comprehension. Detailed assessment was carried out on naming, name comprehension, and probes of semantic knowledge with a battery of 150 items. The patients performed normally on perceptual tests and displayed an item-specific loss of knowledge on the semantic tests. In a primed lexical decision task, greater semantic priming was found relative to age-matched normals. The priming was substantially greater for items with "degraded" representations as determined by the off-line tests. Lexical decision was also performed more slowly on these items. These unexpected results demand a reevaluation of the concepts of the lexicon and semantic memory structure and their possible alteration in dementia.     

Effects of literacy on semantic verbal fluency in an immigrant population

Objective: A significant impact of limited schooling and illiteracy has been found on numerous neuropsychological tests, which may partly be due to the ecological relevance of the tests in the context of illiteracy. The aims of this study were to compare the performance of illiterate and literate immigrants on two semantic criteria for the verbal fluency test, and examine the influence of acculturation on test performances.

Method: Performances of 20 cognitively unimpaired illiterate and 21 literate Turkish immigrants aged ≥50 years were compared on an animal and supermarket criterion for the semantic verbal fluency test. Also, the influence of acculturation on test performances was examined.

Results: Significantly poorer performance of the illiterate compared to the literate group was found for the animal criterion, whereas no differences were found for the supermarket criterion that was considered more ecologically relevant for illiterate individuals. A significant interaction effect was found between the semantic criteria and literacy group, which was mainly related to a large effect of semantic criteria within the illiterate group. Adjusting for years of residence in Denmark and acculturation score did not affect this interaction effect.

Conclusions: Overall, our results are in line with previous studies comparing semantic fluency in illiterate and literate individuals. The results lend further support to the strong associations between literacy, semantic verbal fluency performance and ecological relevance of the semantic criterion and extend previous findings to immigrants with different cultural experiences related to the acculturation process.     

Pervasive influence of semantics in letter and category fluency: a multidimensional approach

We used multidimensional statistical procedures to study semantic and lexical processes underlying word retrieval in verbal-fluency performance. Forty healthy participants were given a two-choice letter task (i.e., generate items beginning with the letter 'A' or 'F', in any order) and a two-choice category task (i.e., generate animal or fruit names, in any order). Using correspondence analysis (CoA) and hierarchical clustering (HC), we found evidence of prominent semantic organization in both letter and category fluency. For example, a striking categorical segregation between animate and inanimate entities emerged during the letter task. Analysis of inter-item times revealed strong sequential priming effects in both tasks. Taken together, these results indicate that semantic facilitation is pervasive in word retrieval processes, even in the letter-fluency task, and therefore suggest that the traditional view of letter fluency as a purely phonemically based task should be revised. Finally, our findings may help explain patterns of verbal-fluency measures obtained in focal brain lesion patients.     

Letter recognition at low contrast levels: effects of letter size

Contrast variation was used to measure recognition thresholds for lowercase letters, with the aim of obtaining a better understanding of the role that early stages of visual processing play in letter recognition. Frequency-of-recognition curves were measured for alphabets of different letter size. Since variation of the adaptational state of the eye changes the characteristics of primary visual processing in a quantifiable way, recognition thresholds were measured both at a high (150 cd m-2) and at a low (0.9 cd m-2) adaptation level. Thresholds decreased as letter size increased, in a way comparable with data on visual acuity. At the lower adaptation level, recognition thresholds became higher, which is also in accordance with visual acuity data. Furthermore, the slopes of the frequency-of-recognition curves for alphabets as a function of log contrast decreased with decreasing letter size. It is argued that this is mainly caused by an increasing dispersion of internal representations of individual letters on the internal psychological scale as letter size decreases.     

Category norms for 500 Spanish words in five semantic categories

This study presents a database of 500 words from five semantic categories: animals, body parts, furniture, clothing, and intelligence. Each category contains 100 words, and data on lexical availability, age of acquisition, imageability, typicality, concept familiarity, written word frequency, and word length in number of syllables are provided with each word. The full set of norms may be downloaded from www.psychonomic.org/archive.     

义符的类别一致性和家族大小影响形声字的语义加工

采用行为实验和眼动技术考察义符的类别一致性和家族大小对形声字语义加工的影响。结果发现：(1) 在一致性判断和视觉选择中均存在着字词水平的类别一致性效应, 义符同整字类别一致的字容易认知。(2) 义符的家族大小影响形声字的语义加工, 义符家族大, 汉语母语者对形声字的加工更容易采用形旁推理策略。(3) 义符家族的类别一致性影响形声字的语义加工。(4) 义符家族的类别一致性和家族大小效应受义符与整字的类别一致性调节。     

The analysis of intuition: Processing fluency and affect in judgements of semantic coherence

In semantic coherence judgements individuals are able to intuitively discriminate whether a word triad has a common remote associate (coherent) or not (incoherent) without consciously retrieving the common associate. A processing-fluency account for these intuitions is proposed, which assumes that (a) coherent triads are processed more fluently than incoherent triads, (b) this high fluency triggers a subtle positive affect, and (c) this affect may be experienced as a cognitive feeling and used in explicit judgement. In line with this account, it was shown that coherent triads (a) are processed faster than incoherent triads (Study 1), (b) serve as positive affective primes (Study 2), and (c) are liked more than incoherent triads (Study 3). When participants were provided with an irrelevant source of their affective reactions, they lost the ability to intuitively discriminate between coherent and incoherent triads (Study 4). Finally, an item-based analysis found that triads that are processed faster are liked more and are more likely to be judged coherent, irrespective of their actual coherence (Study 5).