Speech Evoked Frequency Following Responses to Assess Bilateral Processing in Children with Hearing Loss

Background: Bilateral processing is impaired in children with bilateral cochlear implants even when provided simultaneously at young ages. It is not clear whether children using bilateral hearing aids experience the same deterioration of bilateral processing. In this study, we examined bilateral processing in children with bilateral hearing aids using the speech evoked frequency following response (FFR).

Objectives: 1) To define an objective measure of bilateral advantage in children with normal hearing; 2) to identify abnormalities in bilateral hearing in children with hearing loss using this objective measure.

Methods: A single phoneme, /da/ (Kraus laboratory), was presented to each ear or bilaterally. Levels were at ~50% of the dynamic range (between /da/ maximum comfort level and hearing threshold) and bilaterally balanced using a lateralization procedure previously described. Participants were 9 children with normal hearing (Mean Age = 12.1, SD = 2.5 years) and 6 children with bilateral hearing loss (Mean Age = 14.0, SD = 2.6 years). Expected FFR peaks were measured for amplitude and latency. Responses were also assessed for signal to noise, correlation to the stimulus, and timing delays.

Results: FFRs revealed clear bilateral advantages (amplitude difference between responses to bilateral stimulation and presentation to the ear with the lowest hearing threshold) in the normal hearing group. In children with hearing loss, the FFR had lower signal to noise ratio, increased variability, reduced amplitude responses, and less clear bilateral advantage.

Conclusions: Speech evoked FFR provides a unique opportunity to examine binaural processing in children with and without hearing loss.