Auditory processing deficit in a patient with Rett syndrome.

Because of the consistent and prominent language failure in Rett syndrome, a patient with the characteristic phenotype was tested for subtle auditory processing deficits by visual reinforcement audiometry. In spite of excellent detection threshold and frequency discrimination, frequency sweep discrimination was at a chance level. This discrimination is normally performed by 5-8 month old infants. This observation suggests a defect in the specialized units of the inferior colliculus or higher auditory centers which subserve frequency sweep discrimination.