Clustering and switching strategies in verbal fluency tasks: comparison between schizophrenics and healthy adults.

Verbal fluency tasks are frequently used in clinical neuropsychology. Clustering (the production of words within semantic subcategories) and switching (the ability to shift between clusters) have been described as 2 components underlying fluency performance. We compared the use of clustering and switching in schizophrenic patients and healthy subjects. Seventy-eight schizophrenic subjects (DSM-IV criteria) and 64 control participants matched for age and educational level were recruited. Negative, disorganized, and productive clinical dimensions were evaluated using the SANS and SAPS scales. The number of words generated per semantic-phonemic cluster and the number of switches were evaluated during 2 verbal fluency tasks (phonemic and semantic). In the healthy controls switching and clustering were closely related to the total number of words generated in the verbal fluency tests. The role of the 2 components was partly dependent on the specific task. Switching was prevalent in formal fluency, while both switching and clustering contributed to semantic fluency. In comparison to the healthy controls, the overall group of schizophrenic patients showed a significant impairment of switching in the formal fluency task and of both switching and clustering in the semantic fluency task, and both the negative and disorganized dimensions correlated with verbal fluency performance, the number of swtiches during the phonemic fluency task, and the clustering during semantic fluency task.     

Verbal fluency in Huntington's disease: a longitudinal analysis of phonemic and semantic clustering and switching

Two underlying components of verbal fluency tasks have been identified as clustering (the ability to generate successive words within a sub-category) and switching (the ability to shift from one sub-category to another). Selective impairment of switching ability occurs in patients with frontostriatal pathology, whilst clustering ability is compromised with temporal lobe dysfunction. Letter fluency tasks have been shown to be especially sensitive to frontostriatal deficits, whereas, category fluency tasks tend to be compromised by temporal lobe pathology. This study examined two types of verbal fluency task (letter fluency and category fluency) using two levels of analysis (phonemic and semantic) for clustering and switching measures. The performance of 21 frontostriatally compromised Huntington's disease (HD) patients was followed over an average of 3.5 annual follow-up visits. HD patients showed a significant reduction of correctly generated words over time, together with a significant increase in word repetitions. Phonemic switching decreased significantly over time for both letter and category fluency. Semantic switching, however, remained stable over time for both verbal fluency tasks. Clustering (both semantic and phonemic) likewise remained stable and did not vary longitudinally for either letter or category fluency. Hence, phonemic switching alone drove verbal fluency performance and this selective impairment can be explained by the progressive involvement of frontostriatal circuitry in the natural progression of HD.     

Qualitative analysis of verbal fluency in depression

The aim of this study was to analyze qualitative aspects of verbal fluency in depression. Phonemic and semantic output was scored for word clustering and switching between clusters in depressed patients and normal control subjects. Depressed patients (n=25) and normal control subjects (n=19) were administered both phonemic and semantic fluency tasks. All patients were also evaluated with executive card sorting tests. Patients with depression produced fewer words on the semantic fluency task than controls and showed normal performance on the phonemic fluency tasks. The deficit on semantic fluency of depressed patients was related to a reduced number of switches with normal cluster sizes. The number of switches in depression was associated with a reduced ability to shift mental set on card sorting tests, suggesting that verbal fluency impairment reflects general executive problems in depression.     

Clustering and switching strategies during verbal fluency performance differentiate Alzheimer's disease and healthy aging

Clustering and switching strategies during phonemic and semantic verbal fluency tasks as defined by Troyer et al. (1997), Abwender et al. (2001), and Lanting et al. (2009) were compared using archival data to determine which scoring procedures best differentiate healthy older adults (n = 26) from individuals with early-stage Alzheimer's disease (AD, n = 26). Total word production showed the largest group difference, especially for semantic fluency. The AD group produced fewer switches when compared to the healthy control group, whereas the groups did not differ in cluster size. The AD group also accessed fewer novel semantic subcategories, presumably due to reduced access to semantic memory storage rather than lower processing speed. Clustering and switching scores on the phonemic task did not add information above total words produced, consistent with previous research indicating these variables are most informative in relation to semantic fluency.     

Verbal fluency deficits in Parkinson's disease: a meta-analysis.

A meta-analysis of 68 studies with a total of 4644 participants was conducted to investigate the sensitivity of tests of verbal fluency to the presence of Parkinson's disease (PD) relative to healthy controls. Both phonemic and semantic fluency were moderately impaired but neither deficit qualified as a differential deficit relative to verbal intelligence or psychomotor speed. However, PD patients were significantly more impaired on semantic relative to phonemic fluency (rs =.37 vs.33, respectively), and confrontation naming, a test of semantic memory that imposes only minimal demands upon cognitive speed and effortful retrieval, was associated with a deficit that was of a comparable magnitude to the deficits upon each of these types of fluency. Thus, the disorder appears to be associated with particular problems with semantic memory. Tests that impose heavy demands upon switching may also be disproportionately affected. Demented and non-demented PD patients differ quantitatively but not qualitatively in terms of the relative prominence of deficits on tests of phonemic and semantic fluency. However, patients with dementia of the Alzheimer's type and demented PD patients can be differentiated from one another by the relative magnitude of deficits upon these two measures.     

Normative Data for Clustering and Switching on Verbal Fluency Tasks

Normative data for clustering and switching on verbal fluency tasks are provided. Four hundred and eleven healthy adults between the ages of 18 and 91 were given tests of phonemic fluency (FAS or CFL) and semantic fluency (Animals and Supermarket). Raw scores were corrected for demographic (i.e., age, education, and sex) and test (i.e., fluency form) variables that were determined to make sizable contributions to fluency performance. These normative data should be useful for clinicians and researchers in determining the nature of the fluency impairment in any given individual.     

Normative data for clustering and switching on verbal fluency tasks

Normative data for clustering and switching on verbal fluency tasks are provided. Four hundred and eleven healthy adults between the ages of 18 and 91 were given tests of phonemic fluency (FAS or CFL) and semantic fluency (Animals and Supermarket). Raw scores were corrected for demographic (i.e., age, education, and sex) and test (i.e., fluency form) variables that were determined to make sizable contributions to fluency performance. These normative data should be useful for clinicians and researchers in determining the nature of the fluency impairment in any given individual.     

The verbal fluency task in the Greek population: normative data, and clustering and switching strategies.

We assessed 300 healthy adults in Greece on measures of semantic and phonemic verbal fluency in order to develop norms for the Greek population. We also evaluated the strategies that the participants used spontaneously in order to maximize word production, namely clustering and switching techniques. Our tasks comprised three semantic and three phonemic categories. Consistent with previous investigations of English-speaking samples, we found a contribution of demographic variables to word fluency. Specifically, level of education contributed to total word production, number of switches, and number of repetitive responses on both semantic and phonemic tasks, and the average cluster size only on the phonemic task. Age contributed to total word production and cluster size on the semantic task, and to number of switches on both semantic and phonemic tasks. Sex contributed only to total word production on the semantic task. In our sample, clustering and switching strategies were related to total word production on both tasks, suggesting that these strategies were used effectively. We present tables of normative data stratified by age and level of education. We have also included detailed guidelines for scoring clusters relevant to the Greek population.     

Fonctions cognitives sous-jacentes aux déficits de fluence verbale dans la schizophrénie : revue de la littérature

Individuals with schizophrenia usually show impairment on various cognitive functions, including long-term memory, executive functions and language. Compared to healthy controls, their performance is impaired in verbal fluency tests. These tests require participants to generate in a given time as many words as they can, belonging to a given category (semantic fluency), or beginning with a specific letter (orthographic fluency). Various cognitive functions are involved in verbal fluency tests: psychomotor speed, executive functions, language, long-term verbal memory and semantic memory. The purpose of the present study was to clarify the functional origin of verbal fluency deficits in schizophrenia through a literature review. Nineteen articles were selected in Pubmed and PsycINFO after initial screening and detailed review. They were formally analyzed with regard to general performance, cognitive strategies used in semantic and orthographic fluency tests and, underlying cognitive origin of deficits. Results show that individuals with schizophrenia produce fewer words than healthy controls in both types of fluency tests. Their impairment is more apparent in semantic than in orthographic fluency tests. Results of studies reviewed also show that individuals with schizophrenia adopt the same clustering (i.e. production of related words within a subcategory) and switching (i.e. ability to shift between clusters when a subcategory is exhausted) strategies than healthy controls, but less efficiently. Several hypotheses, such as the impairment of executive functions, semantic memory or speed of information processing, were put forward to account for this finding. Interestingly, the few studies in which researchers performed an analysis of the semantic relationships between words produced in fluency tests showed a less semantic coherence among people with schizophrenia than in healthy controls. Such a difference could be explained by disorganization of semantic memory or impairment in the activation of conceptual representations in semantic memory. Studies in which correlations and regression analyzes were performed allow for clarifying the cognitive origin underlying verbal fluency deficits in schizophrenia. The links between these deficits and information processing speed as well as working memory are well established. These two cognitive domains also appear to be strong predictors of performance in semantic and orthographic fluency tasks in schizophrenia. Individuals with schizophrenia usually present with a significant slowdown in the speed of information processing. Such a slowdown is likely to account for their poor performance in verbal fluency tests, which require the independent and rapid production of words. Working memory disorders are also core cognitive symptoms of schizophrenia. Working memory is involved in verbal fluency tests since they involve “strategic” activation of verbal information in long-term memory, inhibition of inappropriate words, switching between clusters, etc. However, the concept of working memory also partially encompasses the notion of executive functions so that the results reported in the present literature review, according to which impairment of verbal fluency in schizophrenia results from working memory deficits but not from executive functions deficits, are difficult to interpret. Results are also less clear-cut in regard to verbal long-term memory and to language abilities. Finally, numerous studies had shown that individuals with schizophrenia present specific deficits in the organization of semantic memory. However, the impact of this deficit on verbal fluency was explored in one study only. To conclude, verbal fluency tests are sensitive to various neurocognitive conditions and are helpful for differential diagnosis. Further studies are still needed to clarify the functional origin of verbal fluency deficits in schizophrenia, in particular the differential role of executive functions and working memory as well as the impact of semantic memory impairment.     

Verbal fluency in adults with high functioning autism or Asperger syndrome

The semantic and phonemic fluency performance of adults with high functioning autism (HFA), Asperger syndrome and a neurotypical control group were compared. All participants were matched for age and verbal ability. Results showed that the participants with HFA were significantly impaired in their performance of both semantic fluency tasks and the phonemic fluency task using the letter M. The Asperger group was only impaired in their performance of the semantic fluency task ‘professions’. The social components of the ‘professions’ task may have influenced the performance of the two disorder groups for this subtest negatively. The fluency deficits could not be attributed to a lack of the use of strategies or to difficulties in switching between strategies. The impairment in two of the three verbal fluency subtests in the HFA group can be attributed to the relatively low processing speed found in this group.     

Qualitative analysis of verbal fluency before and after unilateral pallidotomy

This study examined qualitative aspects of phonemic and semantic fluency before and after unilateral pallidotomy in patients with intractable Parkinson's Disease (PD). Specifically, clustering (number of similar words generated sequentially) and switching (number of changes or switches from one cluster to another) were evaluated for both fluency tasks. Twenty-five PD patients participated and were grouped according to whether they improved or declined on each of the fluency measures after surgery. Decliners evidenced decreased switching, but not clustering, suggesting difficulties with set-shifting and cognitive flexibility rather than a diminished semantic store of information or retrieval difficulties. Though consistent with hypotheses about difficulties with executive processing after pallidotomy, a series of correlational analyses with composite measures of neuropsychological functioning (attention, language, executive processing, and memory) suggest caution in interpreting these findings. In these analyses, clustering was not meaningfully related to any of the composites whereas switching was significantly and positively related to the composites; this pattern emerged, for the most part, on both fluency measures before and after surgery. Switching, but not clustering, was also significantly and positively correlated with total words generated on both semantic and phonemic fluency. Switching changes across time were also related to DRS changes post-pallidotomy. These correlational analyses challenge the specificity of the switching variable and, more broadly, the validity of these qualitative measures of verbal fluency.     

Effects of the dopamine agonist piribedil on prefrontal temporal cortical network function in normal aging as assessed by verbal fluency

Normal aging has been associated with impaired performance in verbal fluency suggesting a prefrontal temporal cortical network (PFTCN) deficiency. In this study, we investigated the effects of a 2-month treatment period with a dopaminergic agonist (DA) on PFTCN function. Forty healthy, elderly volunteers were assessed on semantic and phonemic verbal fluency after two months of a placebo or a DA treatment (i.e. piribedil 50 mg/day) in a double-blind crossover design. Protocols were scored considering clustering, (i.e. production of words within semantic or phonemic categories, depending on the integrity of temporal lobe), and switching (i.e. the ability to shift between clusters, depending on frontal lobe functioning). Results revealed no significant main effect of the DA treatment on either verbal fluency variables but showed a significant interaction with working memory capacities, with high-capacity span subjects improving phonemic switching on DA whereas low-capacity span subjects performed more poorly on the drug than off. These data are consistent with the literature and confirm the crucial link between working memory capacities and dopamine agonist effects. The present study also provides evidence that pharmacological remediation of age-related cognitive decline has to be taken into consideration.     

Differential prefrontal and frontotemporal oxygenation patterns during phonemic and semantic verbal fluency

Movement artifacts are still considered a problematic issue for imaging research on overt language production. This motion-sensitivity can be overcome by functional near-infrared spectroscopy (fNIRS). In the present study, 50 healthy subjects performed a combined phonemic and semantic overt verbal fluency task while frontal and temporal cortex oxygenation was recorded using multi-channel fNIRS. Results showed a partial dissociation for phonemic and semantic word generation with equally increased oxygenation in frontotemporal cortices for both types of tasks whereas anterior and superior prefrontal areas were exclusively activated during phonemic fluency. Also, a general left-lateralization was found being more pronounced during semantic processing. These findings line up with earlier imaging and lesion studies emphasizing a crucial role of the temporal lobe for semantic word production, whereas phonemic processing seems to depend on intact frontal lobe function.     

Component analysis of verbal fluency in patients with mild traumatic brain injury

We set out to examine the sensitivity of switching and clustering component scores of verbal fluency in patients with mild traumatic brain injury (mTBI). Clustering and switching scores were compared between patients with mTBI and healthy normal controls as well as those with moderate TBI and severe TBI. Fifty-four healthy controls along with 20 mild TBI, 8 moderate TBI, and 12 severe TBI patients were included in the study. Our findings demonstrate that component score effect sizes were larger than those of total words generated for both phonemic and semantic fluency. This pattern of finding held true regardless of comparison group. In addition, semantic fluency component scores were found to correspond to larger component score effect sizes than did phonemic fluency component scores. Our findings demonstrate that component scores derived from the Controlled Oral Word Association Test may be sufficient to reliably capture the effects of unremitting injury (i.e., more than 3 months post status) to the frontal and temporal brain as evinced in cases of unremitting mTBI. This differential pattern of performance provides preliminary evidence for the potential usefulness of switching and clustering in the assessment of mTBI. Given the small sample sizes employed in our study, however, future studies are needed to determine whether component measures of verbal fluency have discriminative ability.     

Verbal fluency performance in dementia of the Alzheimer's type: a meta-analysis

A meta-analysis of 153 studies with 15,990 participants was conducted to compare the magnitude of deficits upon tests of phonemic and semantic fluency for patients with dementia of the Alzheimer's type (DAT) relative to healthy controls. As has been found for patients with focal temporal cortical lesions (but not for patients with focal frontal cortical lesions), DAT patients were significantly more impaired on tests of semantic relative to phonemic fluency (r=0.73 and 0.57, respectively). Thus, since phonemic and semantic fluency are considered to impose comparable demands upon executive control processes such as effortful retrieval, but the latter is relatively more dependent upon the integrity of semantic memory, these results suggest that the semantic memory deficit in DAT reflects a degradation of the semantic store. Also supporting this conclusion, confrontation naming, a measure of semantic memory that imposes only minimal demands upon effortful retrieval, was significantly more impaired than phonemic fluency (r=0.60 versus 0.55, respectively). However, since semantic fluency was also significantly more impaired than confrontation naming (r=0.73 versus 0.61), deficits in semantic memory and effortful retrieval may be additive. Semantic, but not phonemic fluency, was significantly more impaired than measures of verbal intelligence and psychomotor speed. Thus, the semantic memory deficit in DAT qualifies as a differential deficit, but executive dysfunction as indexed by phonemic fluency does not constitute an additional isolated feature of the disorder. Dementia severity was not significantly related to the relative magnitude of deficits upon phonemic and semantic fluency.     

Verbal fluency in bilingual Spanish/English Alzheimer's disease patients

Studies have demonstrated that in verbal fluency tests, monolinguals with Alzheimer's disease (AD) show greater difficulties retrieving words based on semantic rather than phonemic rules. The present study aimed to determine whether this difficulty was reproduced in both languages of Spanish/English bilinguals with mild to moderate AD whose primary language was Spanish. Performance on semantic and phonemic verbal fluency of 11 bilingual AD patients was compared to the performance of 11 cognitively normal, elderly bilingual individuals matched for gender, age, level of education, and degree of bilingualism. Cognitively normal subjects retrieved significantly more items under the semantic condition compared to the phonemic, whereas the performance of AD patients was similar under both conditions, suggesting greater decline in semantic verbal fluency tests. This pattern was produced in both languages, implying a related semantic decline in both languages. Results from this study should be considered preliminary because of the small sample size.     

Verbal fluency component analysis in adults with HIV/AIDS

The present study examined the impact of HIV disease severity, depressed mood, and highly-active antiretroviral therapy (HAART) on verbal fluency components in a sample of adults with HIV-infection. Switching and clustering have been identified as dissociable components that contribute to performance on tests of phonemic and semantic verbal fluency. Advanced HIV-infection was predicted to differentially impair switching. Switching has been shown to be reduced in disorders affecting frontal-striatal systems (e.g., Parkinson's disease). Verbal fluency protocols (FAS and Animals) of 217 adults with HIV-infection were scored for total switches and average cluster size following the method of Troyer, et al. (1998). Component scores were compared to published norms. Analysis of variance (ANOVA) was used to examine the impact on switching and clustering performance of (1) HIV disease severity (presence of AIDS diagnosis) and depressed mood, and (2) AIDS diagnosis and medication status (current HAART therapy). FAS switching was more often impaired in participants with AIDS. Depressed mood did not affect switching. Neither AIDS diagnosis nor depressed mood was associated with clustering performance. Participants with an AIDS diagnosis who were receiving HAART showed better performance on FAS switching relative to participants with AIDS who were not taking antiretroviral medication. FAS switching appears to be sensitive to cognitive changes associated with advanced HIV-infection. Further research is needed to determine if switching is a specific marker of frontal-striatal dysfunction in this population.     

The association between endogenous free testosterone and cognitive performance: a population-based study in 35 to 90 year-old men and women

The relationship between testosterone (T) and cognition has yielded conflicting evidence, showing both positive and negative influences of T on cognitive performance. The association between free testosterone (FT) and cognition was revisited in a large population-based sample of 1276 women and 1107 men (35-90 years of age), assessed individually on visuospatial, verbal fluency, semantic, and episodic memory tasks. For men, higher FT levels were associated with better visuospatial abilities, semantic memory, and episodic memory, with greater positive influence with increasing age. Statistical covariates included age, education, and select medications. For women, FT was negatively associated with verbal fluency, semantic memory, and episodic memory, although only verbal fluency was significant at conventional alpha levels. These results support the claim that FT exerts sex-specific influences on cognitive performance.     

Verbal memory and verbal fluency in adolescents with schizophrenia spectrum disorders

Aim: Although impaired verbal memory and verbal fluency are frequently found in adults with schizophrenia, there has been a paucity of studies investigating adolescents with schizophrenia. Thus, the aim of the present study was to investigate the main subcomponents of verbal memory and verbal fluency in adolescents with schizophrenia spectrum disorders. Methods: Verbal learning and memory and verbal fluency was assessed in 21 adolescents with schizophrenia spectrum disorders (mean age, 15.4 years) compared with 28 healthy adolescents (mean age, 15.1 years). Results: The patient group performed significantly below healthy controls on measures of learning, delayed recall and on a frequency estimation task. No differences between the groups were found for measures of recognition, retention, implicit memory, or susceptibility to interference. Although they had impaired delayed recall the patients remembered most of what they actually learned. The patient group was impaired on phonological and semantic fluency, but there were no differences between the groups with respect to clustering or switching on the fluency tasks, when controlling for total output. There was no disproportionate impairment in semantic, as compared to phonological fluency, in the patient group. Conclusions: Adolescents with schizophrenia spectrum disorders exhibit impairments in verbal learning and verbal fluency, which might have an impact on the individual's everyday functioning.     

Comparative analysis of qualitative verbal fluency performance in normal elderly and demented populations.

Verbal fluency tasks are commonly used in the assessment of patients with known or suspected dementia. Whereas total word production is often analyzed, less attention has been paid to qualitative aspects of verbal fluency performance. The purpose of this study was to examine the diagnostic utility of a qualitative scoring technique for semantic and phonemic fluency tasks in individuals with Alzheimer's disease (AD), Parkinson's disease (PD) with and without dementia, and in a group of older normal controls (ONC). In addition to total words produced, the groups were compared on their use of clustering (i.e., ratio of words generated within subcategories) and switching (i.e., frequency of shifts between clusters) strategies as originally defined by Troyer et al. (1997a). In terms of total number of words produced, controls were superior to the AD and demented PD subjects, who performed similarly. A similar trend was found in relation to switching and clustering scores. PD patients without dementia performed similar to the ONC group on semantic fluency, but were impaired relative to controls on all phonemic fluency variables (i.e., total words produced, clustering, switching). Discriminant function analyses using the three fluency variables revealed that total words was equal to or surpassed the other variables in distinguishing the groups, suggesting that these qualitative verbal fluency features may not provide significant additional information in terms of diagnostic utility.