Impairment of pseudo-word and complex-sound segmentation in dyslexia

Kujala, T.1,2, Halmetoja, J.2, Leinonen, S.3, Lyytinen, H.3, Näätänen, R.2, and Sussman, E.4
1Helsinki Collegium for Advanced Studies, University of Helsinki, Finland; 2Cognitive Brain Research Unit, Department of Psychology, University of Helsinki, Finland; 3Department of Psychology, University of Jyväskylä, Finland; 4Department of Neuroscience, Albert Einstein College of Medicine, NY

Dyslexic individuals have speech- and non-speech sound discrimination dysfunctions even at the early level of cortical discrimination as suggested by mismatch negativity (MMN) studies. For example, discrimination of features such as temporal patterns and pitch are problematic for dyslexic individuals, whereas their sound-duration discrimination is not affected. We evaluated how duration changes in segments of 3-syllable pseudo-words and their acoustic correlates were pre-attentively and attentively discriminated by dyslexic and control adults. Consistently with previous results, no MMN amplitude differences were found between the groups for duration changes, whereas there was a MMN topography difference between the groups for the change in the last tone segment. In addition, the N2b, elicited while attending to the sounds, was smaller in the dyslexic than control subjects for the tone changes in all three segments and for the pseudo-words in the last segment. Furthermore, the dyslexic subjects were impaired in behaviorally discriminating the deviant segments. These results suggest that even such sound contrasts that are discriminated at the early sensory memory level in dyslexic individuals may be difficult to identify when presented in words or comparable complex sounds.