Linguistic and nonlinguistic auditory processing of rapid vowel formant (F2) modulations in university students with and without developmental dyslexia.

To help resolve the issue of whether developmental dyslexia (DD) is related to central auditory processing deficits or to language-specific processing deficits, we had nine dyslectic and nine nondyslectic right-handed undergraduate students perform linguistic (Experiment 1: phoneme identification) and nonlinguistic (Experiment 2: formant rate change detection) tasks. In Experiment 1, subjects listened to synthetic vowels whose second formant (F2) was modulated sinusoidally with F1, F3, and F4 held constant. F2 modulation rate (4-18 Hz) was manipulated within and across stimuli. The groups did not differ in phoneme identification. Experiment 2 was run three times and showed that the control subjects' performance improved across runs whereas the dyslexics' deteriorated across runs (p < .0001), suggesting practice and fatigue effects, respectively. Performance on the two experiments correlated significantly and negatively for the dyslexic subjects only. These results suggest that resource depletion or frontal lobe dysfunction may be implicated in developmental dyslexia.