Auditory frequency discrimination in adult developmental dyslexics.

Developmental dyslexics reportedly discriminate auditory frequency poorly. A recent study found no such deficit. Unlike its predecessors, however, it employed multiple exposures per trial to the standard stimulus. To investigate whether this affects frequency discrimination in dyslexics, a traditional two-interval same-different paradigm (2I_1A_X) and a variant with six A-stimuli per trial (2I_6A_X) were used here. Frequency varied around 500 Hz; interstimulus interval (ISI) ranged between 0 and 1,000 msec. Under 2I_1A_X, dyslexics always had larger just noticeable differences (JNDs) than did controls. Dyslexic and control JNDs were equal at shorter ISIs under 2I_6A_X, but dyslexics became worse than controls at longer ISIs. Signal detection analysis suggests that both sensory variance and trace variance are larger in dyslexics than in controls.