Brainstem plasticity and modified loudness following short-term use of hearing aids

Abstract

Previous research has shown that the threshold of the middle ear acoustic reflex is modified in adult listeners following 1 week of continuous monaural sensory deprivation [Munro and Blount, J. Acoust. Soc. Am. 126, 568-571 (2009)]. The results of the present study provide evidence of plasticity in the brainstem of adult listeners following monaural auditory stimulation. Acoustic reflexes were obtained at a higher sound pressure level in the ear that had been fitted with a low-gain hearing aid for 5 days. These changes are in the opposite direction to those reported after sensory deprivation and are consistent with a gain control mechanism mediated by a process within the brainstem. Stimuli were reported as less loud after hearing aid use but the relationship with changes to the acoustic reflex threshold was not statistically significant.

Using acoustic reflex threshold, auditory brainstem response and loudness judgments to investigate changes in neural gain following acute unilateral deprivation in normal hearing adults

“…The change was observed in both ears and of a similar magnitude at 0.5 and 2 kHz, despite a difference in earplug attenuation at these frequencies. A similar pattern of change between the ears has also been reported after unilateral earplug use (Munro et al, 2014) and unilateral acoustic stimulation (Munro and Merrett, 2013). For example, using the categorical loudness test (Cox et al, 1997), Munro et al (2014) reported a 5 dB decrease in sound level required to match pre-treatment loudness, at 0.5 and 2 kHz in both ears of normal hearing listeners after 7 days of unilateral earplug use.…”

No change in the acoustic reflex threshold and auditory brainstem response following short-term acoustic stimulation in normal hearing adults

“…Participants 153 were asked to wear the hearing aid(s) for 7 days, with a 7 day wash-out period separating the 154 two treatments. The duration of the study was based on the length of time used in previous 155 auditory stimulation studies that have investigated changes in ART and/or loudness in normal 156 hearing listeners (Formby et al, 2003;Formby et al, 2007;Munro and Merrett, 2013). The 157 wash-out period between treatments was justified by the findings of Formby et al (2003): a 158 one week period between treatments was sufficient for loudness to return to pre-treatment 159 levels.…”

“…Other aspects regarding the 419 design of the present study were similar to previous studies. The duration of hearing aid use 420 on a daily basis is comparable to that of Munro and Merrett (2013). In both studies, the 421 participants were asked to wear the hearing aids continuously, except for bedtime.…”

“…Therefore, fine tuning was carried out until the participants deemed 182 the level of amplification comfortable. Compared to Munro and Merrett (2013), 183 approximately 2-3 dB less amplification (identical for the unilateral and bilateral condition) 184 was provided in order for the participants to tolerate the hearing aids (Fig. 1).…”

“…The reference 172 microphone was disabled during the aided measurements to reduce errors due to amplified 173 sound leakage from the non-occluded ear canal. The level of amplification provided by the 174 hearing aids was based on the study of Munro and Merrett (2013) that found that unilateral 175 amplification with a REIG of 15-20 dB (2-4 kHz) was acceptable to normal hearing listeners. 176…”