Capacity of short-term memory in dyslexia is reduced due to less efficient utilization of items’ long-term frequency

Dyslexia, defined as a specific impairment in decoding the written script, is the most widespread learning difficulty. However, individuals with dyslexia (IDDs) also consistently manifest reduced short-term memory (STM) capacity, typically measured by Digit Span or non-word repetition tasks. In this paper we report two experiments which test the effect of item frequency and the effect of a repeated sequence on the performance in STM tasks in good readers and in IDDs. IDDs’ performance benefited less from item frequency, revealing poor use of long-term single item statistics. This pattern suggests that the amply reported shorter verbal spans in dyslexia may in fact reflect their impaired sensitivity to items’ long-term frequency. For repeated sequence learning, we found no significant deficit among IDDs, even when a sensitive paradigm and a robust measure were used.