Tuesday, February 4, 2020

Digit Span in Dyslexia: Variations According to Language Comprehension and Mathematics Skills

Helland, T., & Asbjørnsen, A. (2004). Digit span in dyslexia: Variations according to language comprehension and mathematics skills. Journal of Clinical and Experimental Neuropsychology, 26(1), 31–42. https://doi.org/10.1076/jcen.

Working memory is the ability to hold and manipulate information in the current focus of attention. The ability to just hold information – to store it briefly in mind – has been referred to as short-term memory. We can assess the ability to briefly hold phonological (speech) sound information in mind by asking someone to immediately repeat a list of spoken digits in the correct order (digit span forward). We can assess the ability to both hold phonological information in mind and manipulate it by asking someone to immediately repeat a list of spoken digits in the reverse order from how they were presented (digit span backward task). In both the digit span forward and backward tasks, phonological short-term memory (i.e., the phonological loop) is assessed. In the digit span backward task, working memory is assessed by additionally requiring the manipulation of item order.

This study focused on digit span performance in children with dyslexia. It has been suggested that children with dyslexia have impairments in the phonological loop because they perform poorly on digit span tasks—they might struggle with holding the numbers in their mind in general, rehearsing the correct order, or have difficulty with increased cognitive load. This study also considers two other important factors: (1) other language and/or mathematical problems that could impact span performance, and (2) the use of compensatory strategies during digit span performance. The present study was therefore conducted to systematically investigate digit span performance across subgroups of children dyslexia (and other language/math problems) while controlling for strategy use.

Participants were 20 typically developing children and 37 children with dyslexia. Children with dyslexia were further subgrouped into three groups: children with dyslexia only (n = 12), children with dyslexia and math impairments only (n = 9), and children with dyslexia and language impairments who may also be impaired in math skills (n = 16). All children completed a test of intelligence, and forward and backward digit span tasks without using strategies (e.g., no finger-counting or lip reading).

Results revealed that children with dyslexia only did well in the digit span forward task and poor in the digit span backward task. Children with dyslexia and math impairments did poor on both the digit span forward and digit span backward tasks. Notably, both groups were especially poor at the digit span backward task, and struggled to remember numbers in the latter part of the list, suggesting a difficulty with increased load. In contrast, children with dyslexia and language impairments were able to recall the earlier and latter parts of the list but recalled less digits overall. This suggested a joint language and storage problem.

Findings from this work demonstrates that differences in span performance in children with dyslexia may have clinical implications. It could help us speculate about effects on reading, writing, and math skills. For instance, for children with dyslexia and for those with additional math problems, difficulties with reading and writing may be especially apparent when the cognitive load is high. Children with dyslexia with impaired language skills, on the other hand, might have language comprehension and retention problems more generally.

Blogger: Theresa Pham is a student in the combined SLP MClSc/PhD program, supervised by Dr. Lisa Archibald.

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