Verbal Fluency: A measure of intelligence

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Tests of verbal ability have been used by many years (Thurstone, 1938; Jones-Gotman & Milner, 1977). On this test, subject is presented with a category (e.g.words beginning with ‘M’, or names of animals) and is asked to produce as many examples of these as possible within a given time of period.

Verbal fluency has demonstrated to be impaired in dysphasic patients, but also in patients with lesions on the left (Benton, 1968) and right frontal lobe (Pendleton et al., 1982).

Naming performance has been used to test disabilities in the population. Longitudinal studies show that naming performance changes across the life span, declining specially in oldest subjects (Au et al., 1995), which reflects a breakdown in perceptual and semantic processes.

 One of the most usual tests for examining this ability is the Boston Naming Test (BNT) and the Parietal Lobe Battery. The BNT enjoys and reach database in different countries and different pathologies, as well as normative data across age range.

One important point in fluency tasks is the category of the word. When we test people with mild dementia they perform better naming animals than naming words with specified letter on the beginning, which means that category structure influences retrieval processes (Rosen, 1980).

To test naming fluency is important to control the age of the participants. An effect of aging is observed specially after forty years age and a decline of the verbal ability after the sixties (Rodriguez-Aranda & Martinussen, 2006).

Naming ability is mediated by different strategies. When we compare two measures of verbal fluency, initial letter versus excluded letter (words produced not containing a designated letter), we found that both fluency tasks rely on verbal ability and articulation speed. Excluded letter fluency performance rely more on speak and executive function (Hughes & Bryan, 2002).

Verbal fluency is also a measure of verbal intelligence. In the study of Miller (Miller, 1984), they compared verbal fluency in two groups of patients, one with focal lesions and another with dementia. They use regression to predict fluency from an index of verbal intelligence. When verbal intelligence was taking into account using regression equation, they found that impaired fluency is a specific phenomenon following frontal lesions and not a consequence of intellectual deterioration in dementia.

The most used test of verbal fluency is the FAS. It consists on a task in which the participant has one minute to generate words beginning with each letter ‘F’, ‘A’, ‘S’ (phonemic fluency) and  animal names (semantic fluency). The FAS has been shown to be more sensitive to the effects of education than age: the number of words increases as the level of education increase, while remains constant until age 60  (Tombaugh, Kozak, & Rees, 1999). Other studies have shown that level of education but not age or gender significantly influence verbal fluency (Mathuranath et al., 2003).

Neural correlates of fluency task

Letter and category fluency tasks are associated with frontal and temporal lobe. Letter fluency presents greater activation in left pre-central and inferior frontal gyrus, while category fluency presents greater activation in left middle frontal gyrus and left fusiform gyrus.

Location and cortical activity can be modulated by varying verbal fluency task demands. Right hemisphere activation is greater during automatic speech in response to over-learned category while left hemisphere activation is greater in letter fluency tasks when demands are on executive function (Birn et al., 2010). Furthermore, the uncinate fasciculus shows positive correlation with Boston Naming Test (Catani et al., 2013).

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Au, R., Joung, P., Nicholas, M., Obler, L. K., Kass, R., & Albert, M. L. (1995). Naming ability across the adult life span. Aging, Neuropsychology, and Cognition, 2(4), 300-311. doi:10.1080/13825589508256605

Benton, A. L. (1968). Differential behavioral effects in frontal lobe disease. Neuropsychologia, 6, 5360.

Birn, R. M., Kenworthy, L., Case, L., Caravella, R., Jones, T. B., Bandettini, P. A., & Martin, A. (2010). Neural systems supporting lexical search guided by letter and semantic category cues: A self-paced overt response fMRI study of verbal fluency. NeuroImage, 49(1), 1099-1107. doi:10.1016/j.neuroimage.2009.07.036

Catani, M., Mesulam, M. M., Jakobsen, E., Malik, F., Martersteck, A., Wieneke, C.,… Rogalski, E. (2013). A novel frontal pathway underlies verbal fluency in primary progressive aphasia. Brain, 136(8), 2619-2628. doi:10.1093/brain/awt163

Hughes, D. L., & Bryan, J. (2002). Adult Age Differences in Strategy Use During Verbal Fluency Performance. Journal of Clinical and Experimental Neuropsychology, 24(5), 642-654. doi:10.1076/jcen.24.5.642.1002

Jones-Gotman, M. & Milner, B. (1977). Design fluency: The invention of nonsense drawings after focal cortical lesions. Neuropsychologia, 15, 653-674.

Mathuranath, P. S., George, A., Cherian, P. J., Alexander, A., Sarma, S. G., & Sarma, P. S. (2003). Effects of Age, Education and Gender on Verbal Fluency. Journal of Clinical and Experimental Neuropsychology, 25(8), 1057-1064. doi:10.1076/jcen.25.8.1057.16736

Miller, E. (1984). Verbal fluency as a function of a measure of verbal intelligence and in relation to different types of cerebral pathology. British Journal of Clinical Psychology, 23(1), 53–57. doi:10.1111/j.2044-8260.1984.tb00626.x

Pendleton, M. G., Heaton. R. K.. Lehman, R. A. W. & Hulihan, D. (1982). Diagnostic utility of  the Thurstone word fluency test in neuropsychological evaluation. Journal of Clinical Neuropsychology, 4, 307-3 17.

Rodriguez-Aranda, C., & Martinussen, M. (2006). Age-Related Differences in Performance of Phonemic Verbal Fluency Measured by Controlled Oral Word Association Task (COWAT): A Meta-Analytic Study. Developmental Neuropsychology, 30(2), 697-717. doi:10.1207/s15326942dn3002_3

Rosen, W. G. (1980). Verbal fluency in aging and dementia. Journal of Clinical Neuropsychology, 2(2), 135-146. doi:10.1080/01688638008403788

Thurstone. L. L. (1938). Primary Mental Abilities. Chicago: Chicago University Press

Tombaugh, T. N., Kozak, J., & Rees, L. (1999). Normative Data Stratified by Age and Education for Two Measures of Verbal Fluency: FAS and Animal Naming. Archives of Clinical Neuropsychology, 14(2), 167-177. doi:10.1016/S0887-6177(97)00095-4


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