Reduced Benefit from Long-term Item Frequency Contributes to Short-term Memory Deficits in Dyslexia

Dyslexia, a specific difficulty in acquiring proficient reading, is also characterized by reduced short-term memory (STM) capacity, which is often attributed to poor phonological memory. However, while it is well established that performance in STM tasks is greatly influenced by the frequency of the comprising items, the effect of item frequency in a span task on the performance of Individuals with Developmental Dyslexia (IDDs) has not been tested until recently. Kimel and colleagues (Kimel et al. 2020; Kimel, Lieder, and Ahissar 2022) asked this question using syllables with high vs. low frequency, and found that the benefit of syllable frequency to STM is reduced among IDDs. We now test the effect of item frequency on the performance in a standard, widely used, STM assessment - the Digit Span subtest from the Wechsler Adult Intelligence Scale. The task was conducted twice: in native language and in second language. As the exposure to native language is greater than to second language, we predicted that IDDs’ performance in the task administered in native language will reveal a larger group difference as compared to second language, due to IDDs’ reduced benefit of item frequency. The prediction was confirmed, in line with the hypothesis that reduced STM in dyslexia to a large extent reflects reduced benefits from long-term item frequency and not a reduced STM per-se.