Hearing aid processing changes tone burst onset: effect on cortical auditory evoked potentials in individuals with normal audiometric thresholds.

PURPOSE The validity of using the cortical auditory evoked potential (CAEP) as an objective measure of hearing aid outcome has been questioned in the literature due to stimulus modifications caused by hearing aid processing. This study aimed to investigate the effects of hearing aid processing on the CAEP elicited with tone bursts that may have altered onsets. METHOD CAEPs to unprocessed and hearing aid-processed tone bursts were obtained from 16 individuals with normal audiometric thresholds when the onset time, level, and signal-to-noise ratio (SNR) were matched between the 2 conditions. Tone bursts processed by the hearing aid were recorded in an anechoic box and were presented through insert receivers. Unprocessed tone bursts were superimposed with hearing aid noise floor to match the SNR of the hearing aid-processed tone bursts. RESULTS Shortening of rise time and overshoot at the onset of the tone burst were evident in the hearing aid-processed stimuli. Statistical analysis of data showed no significant effects of hearing aid processing on the latency or amplitude of CAEP peaks (p > .05). CONCLUSION The changes in rise time occurring in the tone bursts due to hearing aid processing may not confound CAEP measures that are used to validate hearing aid fitting.