Cortical evoked potentials and the mismatch negativity (MMN) – revisiting MMN’s potential and clinical utility

Abstract

Newborn hearing screening remains an essential national programme, enabling the early dentification of bilateral, congenital paediatric hearing loss in New Zealand (Digby, Purdy, & Kelly, 2019). Effective habilitation after early identification of hearing loss relies on accurate assessment of hearing levels. However, despite our best efforts, accurate objective threshold estimation via auditory-evoked potentials (AEPs), a key step towards appropriate amplification, may be affected by technical factors, threshold step-size, and/or under- or over-estimation of pure tone thresholds (Small & Stapells, 2017). Inaccuracy in estimated thresholds could contribute to variability in hearing aid fitting outcomes that are evident despite hearing aid fitting that includes measurement of real-ear-to-coupler difference (RECD) measures. To overcome this, an objective hearing aid validation technique has been developed that can be performed before reliable behavioural assessment is possible – cortical auditory evoked potentials (CAEPs) with hearing aids in situ (Purdy & Kelly, 2001; Purdy et al., 2005). While CAEPs provide excellent information about stimulus detection and audibility, they do not provide an index for sound discrimination (Duncan et al., 2009). This paper will recommend the importance of EPs (particularly CAEPs), briefly detail their background, and introduce a prospective means to examine sound discrimination in infants – the mismatch negativity (MMN). A project currently underway to determine the utility of a novel, ‘optimised’, MMN approach that aims to improve clinical hearing aid validation and aided outcomes for infants is presented.