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Article Excerpt
IT IS NOW ESTABLISHED THAT PRENATAL exposure to alcohol produces a wide range of morphological and neurobehavioral outcomes that are often referred to as fetal alcohol spectrum disorders (FASD). Neuropsychological studies of FASD have consistently found deficient performance of alcohol-exposed children on tests assessing executive control functioning (Kodituwakku et al., 2001; Mattson et al., 1999). Subsumed under the umbrella term of "executive control functioning" are a number of deliberate attentional processes involved in goal-directed behavior (e.g., set shifting and planning). Numerous researchers have reported that children with FASD perform less competently than controls on the Wisconsin Card Sorting Test, a well-known test of extra-dimensional set shifting (Olson et al., 1998; Coles et al., 1997; Kodituwakku et al., 2001; Mattson et al., 1999). Kodituwakku and colleagues (2001) found that an alcohol-exposed group completed fewer shifts and made more commission and omission errors than controls on a visual discrimination reversal task, suggesting deficient skills in affective set shifting. Researchers have also obtained evidence that alcohol-exposed children are deficient in cognitive planning, as reflected by the performance of these children on look-ahead puzzles, such as the Progressive Planning Test (Kodituwakku et al., 1995) and the California Tower Task (Mattson et al., 1999).
Letter and category fluency tasks and FASD
Consistent with the foregoing research is the finding that children with FASD have difficulty in the flexible generation of verbal and nonverbal responses as reflected by deficient performance on verbal and visual fluency tasks (Schonfeld et al., 2001). The most widely used tests of verbal fluency are letter and category fluency tasks. A typical letter fluency task requires the subject to generate as many words as possible beginning with a specific letter (e.g., F, A, S) under certain constraints imposed by the examiner (e.g., excluding proper nouns) in a limited time period (usually 60 seconds). In the category fluency task the subject is instructed to produce as many exemplars as possible from a semantic category (e.g., animals, fruits and vegetables). In a pilot study of executive control functioning in children with FASD, Kodituwakku et al. (1995) found that the alcohol-exposed group was impaired in letter fluency but not in category fluency relative to normal controls. Mattson and Riley (1999) reported that children with heavy prenatal alcohol exposure produced fewer words than normal controls on both letter and category fluency tasks, although the magnitude of the group difference was more pronounced on letter fluency than category fluency. Schonfeld and colleagues (2001) also obtained evidence that children with substantial alcohol exposure displayed impaired performance on letter and category fluency tasks, compared with normal controls.
Researchers have suggested that letter fluency tasks require the exploration of more subsets of words (e.g., multiple alphabetic permutations of the stem components--such as ba, be, bi, bo--for the generation of words) than category fluency tasks. Hence, letter fluency relies more on strategic search than does category fluency. Category fluency tasks have been characterized as primarily involving retrieval from lexicosemantic memory. There is also evidence that the performance on letter fluency tasks largely depends on the ability in phonemic switching; performance on category fluency tasks depends on the ability in semantic clustering (Ho et al., 2002). Although both types of fluency tasks involve working memory, Rende and colleagues (2002) found that letter and category fluency tasks differentially involved working memory; the placement of additional demands on the phonological loop, the component presumed to hold verbal information, selectively disrupted the performance on a letter fluency task. Furthermore, demands on the sketchpad, the component presumed to hold visual information, impaired the performance on a category fluency task. Thus, it appears that although both the letter and category fluency tasks involve executive control functioning, each relies on distinct cognitive processes that can be selectively impaired in neurological and neurodevelop-mental disorders.
Aims of the study
One aim of the present research was to explore further the question of whether children with fetal alcohol syndrome (FAS) would display a distinct pattern of performance on verbal fluency tasks. The question of whether letter fluency is more sensitive to the effects of prenatal alcohol exposure remains unanswered. As noted above, some researchers studying children with FASD (Kodituwakku et al., 1995) have reported a greater effect of prenatal alcohol exposure on letter fluency than on category fluency, but others (Schonfeld et al., 2001) have failed to find this interaction. It should be noted that the control group in the Schonfeld et al. study had significantly higher verbal abilities than that in the Kodituwakku et al. study. The possibility exists that the cognitive processes tapped by verbal ability measures (e.g., vocabulary) have more commonalities with the processes involved in category fluency than those mediating letter fluency. Therefore, if both the control and FASD groups have low verbal ability, one can expect a significant group difference in letter fluency but not in category fluency.
A second aim of the study was to examine whether there are differential developmental trends in letter and category fluency in children with FAS. Normative studies of fluency in children ages 5 years and older have repeatedly demonstrated that letter (or phonemic) fluency develops at a slower rate than category fluency (Kremin and Dellatolas, 1996; Riva et al., 2000). In a developmental study of children attending Grades 1-5 (ages 5-11), Riva et al. (2000) found a strong age-related linear trend in the development of category fluency....
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