Auditory stream segregation in dyslexic adults

Developmental dyslexia is often associated with problems in phonological pr ocessing based on, or accompanied by, deficits in the perception of rapid a uditory changes. Thirteen dyslexic adults and 18 control subjects were test ed on sequences of alternating tones of high (1000 Hz) and low (400 Hz) pit ch, which at short stimulus onset asynchronies (SOAs) led to perceptual sep aration of the sound sequence into high- and low-pitched streams. The contr ol subjects perceived the tone sequence as connected down to SOAs of 130 ms , with segregation of the streams at shorter SOAs; in dyslexic subjects the segregation occurred already at 210 ms, Auditory stream segregation has pr eviously been shown to impair the detection of phoneme order in segments of speech sounds. The observed aberrant segregation of sound streams in dysle xic subjects might thus contribute to their difficulties in achieving aware ness of phonemes or phoneme order and in the acquisition of literacy.