Maturation of auditory function related to hearing threshold estimations using the auditory brainstem response during infancy

Abstract Objective The objective of this study was to quantify the maturation of the Auditory Brainstem Response (ABR) at discrete periods during infancy and to provide a means to appropriately estimate hearing thresholds when the ABR is immature. Methods A longitudinal study was designed to measure the in situ ABR thresholds of infants using air-conduction tone bursts of 500, 2000 and 4000 Hz. Thresholds were measured using an eardrum-level microphone to eliminate the bias related to coupler-referenced scales such as the dB nHL scale used for adult assessments. Results The study found that the in situ thresholds of a sample of normally developing infants decreased significantly during the first 6 months of life. A comparison of these in situ thresholds with those of normal-hearing adults revealed that the ABR response reached maturity in these infants between 4 and 6 months of age for the frequencies 500 and 2000 Hz but remained immature, or elevated, at 6 months of age for 4000 Hz. Conclusions The maturation of the ABR should be considered during the estimation of an infant's audiogram and subsequent diagnosis.