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

- Four days of unilateral earplug use resulted in a lower sound level to elicit an acoustic reflex.
- The change in the auditory brainstem response (ABR) is in the opposite direction to the change in the ART.
- The ABR amplitude was reduced in the treatment ear and increased in the control ear.
- There was a significant recovery of ART to baseline within 2 h after earplug removal.
- There was no change in loudness after 4 days of unilateral earplug use.

Unilateral auditory deprivation induces a reduction in the acoustic reflex threshold (ART) and an increase in loudness. These findings have been interpreted as a compensatory change in neural gain, governed by changes in excitatory and inhibitory neural inputs. There is also evidence to suggest that changes in neural gain can be measured using the auditory brainstem response (ABR). The present study extended Munro et al. (2014) [J. Acoust. Soc. Am. 135, 315-322] by investigating changes after 4 days of unilateral earplug use to: (i) ART, (ii) ABR and (iii) loudness. Because changes may occur during the post-deprivation test session (day 4), ART measurements were taken 1 h and 2 h post-earplug removal. There was a significant reduction in ART in the treatment ear immediately after the removal of the earplug, which is consistent with a compensatory increase in neural gain. A novel finding was the significant return of ARTs to baseline within 2 h of earplug removal. A second novel finding was a significant decrease in the mean amplitude of ABR wave V in the treatment ear, but a significant increase in the control ear, both after 4 days of deprivation. These changes in the ABR are in the opposite direction to those predicted. We were unable to replicate the change in loudness reported in previous deprivation studies; however, the short period of earplug use may have contributed to this null finding.