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Poor Short-term Memory: A Core Deficit in Dyslexia

One of the most reliable and often-quoted associated characteristics of developmental dyslexia is an inefficiency in short-term memory (STM).

A deficit in STM, together with rapid naming, has been mainly interpreted within the phonological core deficit hypothesis (Trecy, Steve & Martine, 2013; Elliott & Grigorenko, 2014). Verbal STM capacity, measured by digit span or non-word repetition tasks, is typically reduced in children with dyslexia (Snowling, Goulandris & Defty, 1996) and this reduction is still present in adults with a history of dyslexia (Majerus & Cowan, 2016).

Ramus and Szenkovits (2008), however, raised the question whether STM deficits in dyslexia are perhaps a basic impairment, rather than being accounted for by phonological processing difficulties.

In an attempt to answer this question, Trecy, Steve and Martine (2013) distinguished between item and order retention processes. While STM for item information has been shown to depend on the quality of underlying phonological representations, and hence should be impaired in dyslexia, STM for order information is considered to reflect core STM processes independent from language processing.

In their study, 30 adults with dyslexia and 30 control participants were matched for age, education, vocabulary and IQ, and presented with STM tasks that distinguished item and order STM capacities. The researchers observed not only impaired order STM in adults with dyslexia, but this impairment was independent of item STM impairment.

This study shows that adults with dyslexia present a deficit in core verbal STM processes, a deficit that cannot be accounted for by the language processing difficulties that characterize dyslexia. These results support theoretical accounts considering independent order STM and item STM processes, with a potentially causal involvement of order STM processes in reading acquisition.

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References:

Elliott, J. G., & Grigorenko, E. L. (2014). The dyslexia debate. Cambridge: Cambridge University Press.

Majerus, S., & Cowan, N. (2016). The nature of verbal short-term impairment in dyslexia: The importance of serial order. Frontiers in Psychology. https://doi.org/10.3389/fpsyg.2016.01522

Ramus, F., & Szenkovits, G. (2008). What phonological deficit? Quarterly Journal of Experimental Psychology, 61(1), 129-141.

Snowling, M. J., Goulandris, N., & Defty, N. (1996). A longitudinal study of reading development in dyslexic children. Journal of Educational Psychology, 88(4), 653-669.

Trecy, M. P., Steve, M., & Martine, P. (2013). Impaired short-term memory for order in adults with dyslexia. Research in Developmental Disabilities, 34(7), 2211-2223.