Phonological and sensory short-term memory are correlates and both affected in developmental dyslexia

We investigated whether poor short-term memory (STM) in developmental dyslexia affects the processing of sensory stimulus sequences in addition to phonological material. STM for brief binary non-verbal stimuli (light flashes, tone bursts, finger touches, and their crossmodal combinations) was studied in 20 Finnish adults with dyslexia and 24 healthy controls. To determine sensory Item STM, participants were asked to match pairs of sequences of increasing length. In Time STM, participants matched pairs of five-stimulus-sequences of increasing stimulus onset asynchrony between the stimuli. Phonological STM was studied with digit span forwards and backwards, pseudoword span, pseudoword matching span, and pseudoword repetition. Earlier results associating phonological STM impairment with dyslexia were replicated. Dyslexic participants also performed more poorly than controls in sensory STM, suggesting that they have general difficulties in representing temporal sequences in STM. Further, sensory STM, phonological STM, temporal acuity, and reading ability were correlated, pointing to shared processes.