title: Auditory steady state cortical responses indicate deviant phonemic-rate processing in adults with dyslexia.
abstract: OBJECTIVE
  Speech intelligibility is strongly influenced by the ability to process temporal modulations. It is hypothesized that in dyslexia, deficient processing of rapidly changing auditory information underlies a deficient development of phonological representations, causing reading and spelling problems. Low-frequency modulations between 4 and 20 Hz correspond to the processing rate of important phonological segments (syllables and phonemes, respectively) in speech and therefore provide a bridge between low-level auditory and phonological processing. In the present study, temporal modulation processing was investigated by auditory steady state responses (ASSRs) in normal-reading and dyslexic adults.
  
  
  METHODS
  Multichannel ASSRs were recorded in normal-reading and dyslexic adults in response to speech-weighted noise stimuli amplitude modulated at 80, 20, and 4 Hz. The 80 Hz modulation is known to be primarily generated by the brainstem, whereas the 20 and 4 Hz modulations are mainly generated in the cortex. Furthermore, the 20 and 4 Hz modulations provide an objective auditory performance measure related to phonemic- and syllabic-rate processing. In addition to neurophysiological measures, psychophysical tests of speech-in-noise perception and phonological awareness were assessed.
  
  
  RESULTS
  On the basis of response strength and phase coherence measures, normal-reading and dyslexic participants showed similar processing at the brainstem level. At the cortical level of the auditory system, dyslexic subjects demonstrated deviant phonemic-rate responses compared with normal readers, whereas no group differences were found for the syllabic rate. Furthermore, a relationship between phonemic-rate ASSRs and psychophysical tests of speech-in-noise perception and phonological awareness was obtained.
  
  
  CONCLUSIONS
  The results suggest reduced cortical processing for phonemic-rate modulations in dyslexic adults, presumably resulting in limited integration of temporal information in the dorsal phonological pathway.
authors.affiliation: ExpORL, Department of Neurosciences, Katholieke Universiteit Leuven, Leuven, Belgium. hanne.poelmans@med.kuleuven.be
authors.forename: Hanne
authors.initials: H
authors.lastname: Poelmans
authors.forename: Heleen
authors.initials: H
authors.lastname: Luts
authors.forename: Maaike
authors.initials: M
authors.lastname: Vandermosten
authors.forename: Bart
authors.initials: B
authors.lastname: Boets
authors.forename: Pol
authors.initials: P
authors.lastname: Ghesquière
authors.forename: Jan
authors.initials: J
authors.lastname: Wouters
mesh_terms: D001303:Auditory Cortex / Q000503:physiopathology*; D001308:Auditory Perceptual Disorders / Q000503:physiopathology*; D004410:Dyslexia / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009622:Noise; D010700:Phonetics; D011571:Psychoacoustics; D011932:Reading; D013067:Speech Perception / Q000502:physiology*; D055815:Young Adult