On-line version ISSN 1668-7027
MARINO, Julián; ACOSTA MESAS, Alberto and ZORZA, Juan Pablo. Executive control and verbal fluency in child population: Quantitative, qualitative and temporal measures. Interdisciplinaria [online]. 2011, vol.28, n.2, pp. 245-260. ISSN 1668-7027.
Verbal fluency tests (VFTs) are considered semantic cognitive tasks. They demand the retrieval of words under different semantic, phonologic, and grammatical conditions. The measures most commonly used to assess word recall in VFTs are: (1) the number of words produced, (2) categorical and phonological association between words, (3) switching between clusters, and (4) the time at which the words are evoked. These measures involve quantitative (1), qualitative (2 and 3), and temporal (4) analyses. In this study, semantic and phonological VFTs were administered to a child population (8-12 years) in Granada (Spain), in order to: (1) review traditional VFT measures, (2) update temporal indices, and (3) introduce combinations, in an effort to more precisely establish the role of executive control. Topics widely-discussed in the literature include two crucial cognitive processes that underlie VFT performance: semantic processing and executive control, which have been associated with activity in temporal and frontal brain regions, respectively. One of the major challenges in the study of these processes is to distinguish between their separate contributions to VFT execution using obtained data. Measures of switching and clustering have traditionally been used to this end, however they do not take into account the time at which the words are evoked. These measures have also been criticized because their final scores are interrelated and exposed to biases difficult to control. Considering temporal measures important, we evaluated the role of five executive control variables (attentional control, cognitive flexibility, inhibitory control, switching, and sustained control) and their relationship with combined quantitative, qualitative and temporal measures. Time variables were included by placing each word evoked on a sixtysecond timeline of verbal production. This way we were able to simultaneously calculate the clustering and switching of words, and their temporal positions. All of these results were associated with executive measures using predictive association statistical techniques. Significant results were found among those measures that emphasized the combination of temporary and qualitative cluster measures. We were also able to reliably isolate the participation of executive functions such as inhibitory control and cognitive flexibility in the combination of spurts and clusters words. This was determined with Multiple Regression Analysis scores, entering the executive functions as independent variables and each of the verbal fluency measures as dependent variables. For example, an R2 of .41 (.000) was obtained for the abovementioned combination of spurted -clustered words in the phonological VFT letter P, entering Trail Making B and Trenerry's Color-Word version of the Stroop task (Lezak, 1995) as predictor variables. When compared, these values clearly exceed those obtained with traditional quantitative and qualitative measures. We discussed these results in relation to the possibility of developing a more precise executive control index for VFTs, specifically for the rapid transition from one word to another related word. As far as we know, only switching (shifting between clusters of words) has been considered an executive control index in VFTs. Here we propose the combination measures described. Possible cognitive mechanisms related to these findings are discussed. Future research must contemplate: (1) a greater sample size, because only 61 participants were studied here, (2) using other technical measures to determine clustering and switching, (3) improving the executive function measures, (4) including other VFTs, such as letter exclusion or action fluency, and (5) extending the procedure to an adult population.
Keywords : Verbal fluency; Executive functions; Temporal measures; Cognitive control; Prefrontal cortex.