Patterns of deficit in auditory temporal processing among dyslexic adults.

We characterized temporal psychoacoustic performance in a group of adult dyslexics with excellent cognitive abilities. These individuals performed adequately on a two-tone frequency discrimination task when inter-stimulus intervals were long ( > or =1 s or more). However, their performance gradually deteriorated as interval duration was shortened (0.7- 0.1 s). Dyslexics with similar reading abilities, but with average cognitive abilities, performed poorly at all intervals. These findings show that, though both groups suffer from non-phonological deficits in auditory discrimination, the nature of their deficits differs. Dyslexics with excellent cognitive abilities seem to have slow, yet adequate, stimulus identification and comparison mechanisms. The fundamental impairment of the other dyslexic group is difficult to determine because their performance was poor across all intervals.