Frequency-Specific ABR and ASSR Threshold Assessment in Young Infants

The importance of early identification and habilitation of hearing loss for improved access to auditory stimuli and for positive prognosis of speech and language is well established in the literature (American Speech-Language-Hearing Association [ASHA] 2004; Hyde 2005; Joint Commission on Infant Hearing [JCIH] 2007; Kennedy, McCann, Campbell, Kimm and Thornton 2005; Yoshinaga-Itano and Gravel 2001; Yoshinaga-Itano, Sedey, Coulter and Mehl 1998). As a result of the importance of early identification of hearing loss, many countries have established newborn hearing screening programs. Diagnostic audiologic assessment is required for follow-up for infants who do not pass newborn hearing screening, with the goal for most newborn hearing screening, follow-up and intervention programs, including the British Columbia Early Hearing Program (BCEHP), of confirmation and characterization of hearing loss (of a mild degree or worse) by age 3 months, and amplification by the age of 6 months (JCIH 2007). An auditory evoked potential (AEP) with high correlation to behavioral threshold is essential for the young infant population and for those older infants and children where accurate behavioral thresholds cannot be obtained. This chapter describes the two frequency-specific AEP methods currently considered appropriate for infant threshold measures: the tone-evoked auditory brainstem response (ABR), the current gold-standard measure, and the relatively new brainstem auditory steady-state response (ASSR).