Psychophysical sensitivity and physiological response to amplitude modulation in adult dyslexic listeners

This study reports two experiments conducted to assess the sensitivity of d yslexic listeners to amplitude modulation (AM) of acoustic stimuli. The sma llest detectable depth of AM of white noise was measured as a function of m odulation frequency. Dyslexic listeners had significantly higher thresholds of AM depth than did matched control listeners. We also recorded the scalp potential evoked by AM of white noise (the amplitude modulation following response, AMFR). Dyslexic listeners had significantly smaller AMFRs than di d matched control listeners. The reduced AMFR is consistent with reduced se nsitivity to AM, and there was a strong association between these psychophy sical and physiological measures. This deficit in AM sensitivity may result in impaired perception of the AM present in speech.