Kaltenbacher, T. 1, 4 , Pfleiderer, B. . 2 , Bühner, B. . 2 & Breninger, B. . 3, 4
1 University of Salzburg, Dep?t of Linguistics
2 University Hospital Münster, Dep?t of Clinical Radiology, Research Group ?Cognition and Gender
3 University of Salzburg, Dep?t of Communication Sciences
4 Salzburg Institute for Reading Research (SIRR), Salzburg College
Amidst the linguistically oriented approaches to dyslexia, the phonological deficit hypothesis is prominently discussed, and has been examined from a speech perception as well as a phonological representations perspective.
This study explores the ability to process audiovisual speech as well as unimodal visual and acoustic speech signals in adult dyslexic subjects and controls (N=34 - fMRI, N=64 - eyetracking).
We investigated the - potentially subtle - speech signal processing deficit, with an experimental paradigm examining speech processing on a phonemic syllable level, a phonemic pre-lexical level, and a phonemic McGurk task for the fMRI experiment. Stimuli comprised audiovisually congruent speech material, audiovisually incongruent items triggering a McGurk effect, as well as audio and visual only stimuli. Upon presentation of the items, subjects? eye movements were recorded to ascertain that subjects would look at the aspects relevant for speech.
The eyetracking and behavioural data suggest a strong tendency among dyslexic subjects to ignore the visual input in speech perception - hence a McGurk percept is not reliably triggered. The fMRI data suggest that dyslexic subjects do not activate left lateralized language regions as strongly as controls do. These results are discussed against current theories of speech perception and speech processing deficits in dyslexia