The effect of time, automatic and controlled processes on verbal fluency performance in individuals with multiple sclerosis and healthy controls
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Objective: The present study evaluated phonemic and semantic verbal fluency in patients with Multiple Sclerosis (MS) and controls. There is a limited amount of research on the effects of time, and clustering and switching on verbal fluency performance in MS. Using individuals with MS and healthy controls, we aimed to (1) to examine word generation performance over time (i.e., 20, 40, 60-sec time intervals) on phonemic and semantic verbal fluency measures; (2) examine group differences in clustering and switching, and the effect of time and its interactions with these measures of fluency;(3) as well as qualitatively examine frequency exemplars in both groups, Measurements: Verbal fluency output, lexical strategies (clustering and switching) and neurocognitive performance were examined in 30 individuals with relapsing-remitting MS RRMS (mean age in years = 43.5+/-1.8; percent female =90) and 30 healthy controls (mean age in years = 43.2+/-1.7; percent female = 90). Results: Linear mixed effects models revealed a significant effect of time in phonemic fluency with a reduction in number of words generated when comparing the first 20-sec to the second (p<.001) and third (p<.001) intervals. There was a significant effect of time for semantic fluency when comparing the first 20-sec to the second (p.05). Individuals with MS produced less words overall in the semantic fluency task (p=.05). Group differences for the production of mean phonemic cluster sizes were not significant (p>.05), and for semantic cluster sizes it trended towards significance (p=.06). There was a significant effect of time in the mean cluster size produced when comparing the first 20-sec with the second (p<.05) and third (p<.05) intervals in the semantic fluency task. Also, a significant group by time interaction of mean cluster size was produced when comparing the first 20-sec with the last 20-sec interval (p<.05) in the semantic fluency task. While individuals with MS produced less switches for both tasks overall, there were no significant group differences. There was a significant effect of time in the number of phonemic and semantic switches (all p<.05). Conclusion: These findings suggest that for individuals with MS and healthy controls, phonemic and semantic word retrieval is based on the initial automatic production of readily available words that over time becomes more effortful and less productive. A decline in verbal fluency performance in individuals with MS may represent decreased efficiency in accessing semantic memory stores as a function of time, associated with a decline in learning and memory, executive functioning, and speed of processing.