Auditory-evoked potential studies of cortical maturation in normal hearing and implanted children: correlations with changes in structure and speech perception.

Human auditory system maturation as assessed by means of auditory-evoked potential recording is compared to maturation of axon neurofilaments and some critical stages in speech perception. The parallels strongly suggest that the emergence of the N1 component reflects the maturation of the axons in layer II and upper layer III of the auditory cortex. This is also the time period during which the perception of speech in noise and degraded speech markedly improves. The absence of N1 in cochlear implant subjects who have been deaf for a period of at least 3 years below the age of 6 years suggests a critical period in the maturation of the upper cortical layers and potentially poor future performance in the perception of masked and degraded speech.