Verbal and Non‐verbal Fluency in Adults with Developmental Dyslexia: Phonological Processing or Executive Control Problems?

Abstract

The executive function of fluency describes the ability to generate items according to specific rules. Production of words beginning with a certain letter (phonemic fluency) is impaired in dyslexia, while generation of words belonging to a certain semantic category (semantic fluency) is typically unimpaired. However, in dyslexia, verbal fluency has generally been studied only in terms of overall words produced. Furthermore, performance of adults with dyslexia on non-verbal design fluency tasks has not been explored but would indicate whether deficits could be explained by executive control, rather than phonological processing, difficulties. Phonemic, semantic and design fluency tasks were presented to adults with dyslexia and without dyslexia, using fine-grained performance measures and controlling for IQ. Hierarchical regressions indicated that dyslexia predicted lower phonemic fluency, but not semantic or design fluency. At the fine-grained level, dyslexia predicted a smaller number of switches between subcategories on phonemic fluency, while dyslexia did not predict the size of phonemically related clusters of items. Overall, the results suggested that phonological processing problems were at the root of dyslexia-related fluency deficits; however, executive control difficulties could not be completely ruled out as an alternative explanation. Developments in research methodology, equating executive demands across fluency tasks, may resolve this issue. Copyright © 2017 John Wiley & Sons, Ltd.

Verbal fluency in relation to reading ability in students with and without dyslexia

“…Our findings of impaired verbal fluency in the DD group are in line with some of the earlier studies on this population (Brosnan et al, 2002; Hatcher et al, 2002; Smith-Spark et al, 2017; Snowling et al, 1997). A plausible explanation for the generally poorer verbal fluency performance in the DD group is that it reflects impaired frontally regulated executive control (Pennington, 2006; Pennington & Bishop, 2009), general lexical retrieval difficulties (Nation, 2005; Nation, Marshall, & Snowling, 2001; Ullman & Pierpoint, 2005), or impaired speed of processing (McDowd et al, 2011; McGrath et al, 2011; Willcutt et al, 2010).…”

“…It was further hypothesized that the three tasks would correlate weakly to moderately with each other, reflecting partly overlapping and partly unique neurocognitive mechanisms. Due to the assumed greater dependence on phonological skills, letter fluency was expected to correlate more strongly with phonological awareness and RAN, compared to both semantic fluency and action fluency (e.g., Smith-Spark et al, 2017). The results, which partly confirmed our hypotheses, are discussed below.…”

“…Studies of verbal fluency in individuals with dyslexia have examined performance by measuring the number of words produced, some also investigating clustering and switching, in order to clarify their relation to cognitive abilities such as phonological processing and executive function. These studies have pointed out that difficulties in both phonological processing and executive control are possible explanatory factors underlying impairments in verbal fluency in adults with dyslexia (i.e., Mielnik et al, 2015; Smith-Spark et al, 2017).…”

Do measures of memory, language, and attention predict eyewitness memory in children with and without autism?

“…Goddard et al (2014) also reported category fluency to be a significant predictor of autobiographical memory in children with autism. Although measures of verbal fluency are often considered to reflect executive functioning (Pennington & Ozonoff, 1996;Smith-Spark, Henry, Messer, & Ziecik, 2017), there is evidence that they may be more strongly related to language ability (e.g. Henry, Messer, & Nash, 2015).…”

A review of prospective memory impairments in developmental dyslexia: evidence, explanations, and future directions

“…Given that phonemic fluency is an area in which adults with dyslexia have been found to have difficulties (e.g., Brosnan et al, 2002;Smith-Spark, Henry, Messer & Zięcik, 2017), it may well be that at least some of the PM difficulties experienced by people with dyslexia are related to this area of executive functioning and, more particularly, the efficient and flexible access of information in verbal long-term memory (Fisk & Sharp, 2004). Although the argument is more than a little tenuous at present, verbal fluency may provide a link between the contributions of executive functioning deficits and the retrospective memory difficulties considered previously in this section (see also Smith-Spark, Moss et al, 2016).…”