UBC Theses and Dissertations
Slow cortical potential measures of amplification Marynewich, Susan Lindsay
With the advent of Universal Newborn Hearing Screening programs, it has become increasingly common for infants to be fit with hearing aids by six months of age. Due to the inability of infants to actively participate in the hearing aid fitting, there is a need for a reliable and objective measure of hearing aid validation in this population. Slow cortical potentials (SCP) are currently being marketed for the purpose of validating infant hearing aid fittings; however, there is a lack of evidence to support use of SCPs for this purpose. In the current thesis, two studies were carried out: Study A investigated N1-P2 amplitudes and N1 latencies in response to a 60-ms duration tonal stimulus (1000 Hz) presented at three intensities (30, 50 and 70 dB SPL) in aided and unaided conditions using three hearing aids (Analog, DigitalA, DigitalB) with two gain settings (20- and 40-dB). Study B investigated the effects of hearing aid processing on acoustic measures of the stimuli, under the same conditions as Study A, with an additional 757-ms tonal stimulus (1000 Hz). Overall, it was predicted that N1-P2 amplitudes would be larger and N1 latencies shorter in the aided compared with unaided conditions; however, the results showed response amplitudes were smaller for the digital hearing aids compared with the analog hearing aid and none of the hearing aids resulted in a reliable increase in response amplitude relative to unaided across conditions. Additionally, N1 response latencies in analog conditions were not significantly different from unaided N1 latencies; however, both digital hearing aids resulted in significantly delayed N1 peaks. Acoustic recording results obtained in Study B indicate that gain achieved by the hearing aids for both the short and long SCP stimuli was less than real-ear insertion gain measured with standard hearing aid test signals. The effect was more pronounced for the short stimulus. These results suggest that the typical stimuli used for SCP testing may be too brief for the processing time of hearing aids, especially those with digital processing.
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