title: The level of audiovisual print-speech integration deficits in dyslexia.
abstract: The classical phonological deficit account of dyslexia is increasingly linked to impairments in grapho-phonological conversion, and to dysfunctions in superior temporal regions associated with audiovisual integration. The present study investigates mechanisms of audiovisual integration in typical and impaired readers at the critical developmental stage of adolescence. Congruent and incongruent audiovisual as well as unimodal (visual only and auditory only) material was presented. Audiovisual presentations were single letters and three-letter (consonant-vowel-consonant) stimuli accompanied by matching or mismatching speech sounds. Three-letter stimuli exhibited fast phonetic transitions as in real-life language processing and reading. Congruency effects, i.e. different brain responses to congruent and incongruent stimuli were taken as an indicator of audiovisual integration at a phonetic level (grapho-phonological conversion). Comparisons of unimodal and audiovisual stimuli revealed basic, more sensory aspects of audiovisual integration. By means of these two criteria of audiovisual integration, the generalizability of audiovisual deficits in dyslexia was tested. Moreover, it was expected that the more naturalistic three-letter stimuli are superior to single letters in revealing group differences. Electrophysiological and hemodynamic (EEG and fMRI) data were acquired simultaneously in a simple target detection task. Applying the same statistical models to event-related EEG potentials and fMRI responses allowed comparing the effects detected by the two techniques at a descriptive level. Group differences in congruency effects (congruent against incongruent) were observed in regions involved in grapho-phonological processing, including the left inferior frontal and angular gyri and the inferotemporal cortex. Importantly, such differences also emerged in superior temporal key regions. Three-letter stimuli revealed stronger group differences than single letters. No significant differences in basic measures of audiovisual integration emerged. Convergence of hemodynamic and electrophysiological signals appeared to be limited and mainly occurred for highly significant and large effects in visual cortices. The findings suggest efficient superior temporal tuning to audiovisual congruency in controls. In impaired readers, however, grapho-phonological conversion is effortful and inefficient, although basic audiovisual mechanisms seem intact. This unprecedented demonstration of audiovisual deficits in adolescent dyslexics provides critical evidence that the phonological deficit might be explained by impaired audiovisual integration at a phonetic level, especially for naturalistic and word-like stimulation.
authors.affiliation: University Clinics of Child and Adolescent Psychiatry (UCCAP), University of Zurich, Zurich, Switzerland; Neuroscience Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Jens
authors.initials: J
authors.lastname: Kronschnabel
authors.affiliation: University Clinics of Child and Adolescent Psychiatry (UCCAP), University of Zurich, Zurich, Switzerland.
authors.forename: Silvia
authors.initials: S
authors.lastname: Brem
authors.affiliation: Neuroscience Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland; Department of Psychology, University of Zurich, Zurich, Switzerland.
authors.forename: Urs
authors.initials: U
authors.lastname: Maurer
authors.affiliation: University Clinics of Child and Adolescent Psychiatry (UCCAP), University of Zurich, Zurich, Switzerland; Neuroscience Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland; Department of Child and Adolescent Psychiatry and Psychotherapy, Central Institute of Mental Health, Medical Faculty Mannheim/Heidelberg University, Mannheim, Germany; Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland. Electronic address: brandeis@kjpd.uzh.ch.
authors.forename: Daniel
authors.initials: D
authors.lastname: Brandeis
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000704:Analysis of Variance; D001307:Auditory Perception / Q000502:physiology*; D001921:Brain / Q000098:blood supply / Q000473:pathology / Q000503:physiopathology; D004410:Dyslexia / Q000150:complications* / Q000473:pathology; D004569:Electroencephalography; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000097:blood; D010468:Perceptual Disorders / Q000209:etiology*; D010700:Phonetics; D010775:Photic Stimulation; D011930:Reaction Time; D014796:Visual Perception / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: Adolescence; Multisensory integration; Phonological deficit; Planum temporale; Reading; Superior temporal