Non-impaired auditory phase locking in dyslexic adults

DYSLEXIC adults have profound difficulties in discriminating rapidly presented sound sequences. To test whether these deficits might be caused by impaired neuronal phase locking to the envelopes of the sound stimuli, 20 normal-reading and 13 dyslexic adults discriminated pitches of pure tones at similar to 1 kHz (producing spectral pitch due to place coding in the cochlea) and of similar to 80 Hz amplitude modulations of white noise (producing periodicity pitch based on temporal information only). We proposed that a specific deficit in phase locking would result in a worse ability to discriminate periodicity than spectral pitch. The dyslexics were significantly less accurate than the control subjects in discriminating both spectral and periodicity pitch stimuli but their performance was not disproportionally worse in the periodicity pitch task. Thus it seems that impaired neuronal phase-locking cannot explain the problems dyslexics face in processing of rapid sound sequences. NeuroReport 10:2347-2348 (C) 1999 Lippincott Williams & Wilkins.