Auditory stream segregation in dyslexic adults.

Developmental dyslexia is often associated with problems in phonological processing based on, or accompanied by, deficits in the perception of rapid auditory changes. Thirteen dyslexic adults and 18 control subjects were tested on sequences of alternating tones of high (1000 Hz) and low (400 Hz) pitch, which at short stimulus onset asynchronies (SOAs) led to perceptual separation of the sound sequence into high- and low-pitched streams. The control 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 previously been shown to impair the detection of phoneme order in segments of speech sounds. The observed aberrant segregation of sound streams in dyslexic subjects might thus contribute to their difficulties in achieving awareness of phonemes or phoneme order and in the acquisition of literacy.