Speech- and sound-segmentation in dyslexia: evidence for a multiple-level cortical impairment

Developmental dyslexia involves deficits in the visual and auditory domains, but is primarily characterized by an inability to translate the written linguistic code to the sound structure. Recent research has shown that auditory dysfunctions in dyslexia might originate from impairments in early pre-attentive processes, which affect behavioral discrimination. Previous studies have shown that whereas dyslexic individuals are deficient in discriminating sound distinctions involving consonants or simple pitch changes, discrimination of other sound aspects, such as tone duration, is intact. We hypothesized that such contrasts that can be discriminated by dyslexic individuals when heard in isolation are difficult to identify when occurring within words or structurally similar complex sound patterns. In the current study, we addressed how segments of pseudo-words and their non-speech counterparts are processed in dyslexia. We assessed the detection of long-duration differences in segments of these stimuli and identified the brain processes that could be associated with the behavioral results. Consistent with previous studies, we found no early cortical sound-duration discrimination deficit in dyslexia. However, differences between impaired and non-impaired readers were found in the brain processes associated with sound-change recognition as well as in the behavioral performance. This suggests that even when the early, automatic, sound discrimination processes are intact in dyslexic individuals, deficits in the later, attention-dependent processes may lead to impaired perception of speech and other complex sounds.