Comparison of Acoustic Reflex Thresholds Across Different Stimuli

Abstract

Background: Acoustic reflex (AR) is the contraction in the middle ear muscles in response to severe acoustic stimulation. Thresholds of AR can be obtained using different stimuli and different stimulus parameters. However, the reflexes are often difficult to elicit in hearing-related disorders such as hyperacusis, recruitment, young infants, and children with autism. Comparisons of AR thresholds (ARTs) across different stimuli, such as PT, broadband noise, and clicks at different rates, can provide information on the stimuli optimally used for difficult-to-test populations. Objective: The study aimed to estimate and correlate the ARTs elicited by pure-tones (PT), the low-frequency band (low pass [LP]) and high-frequency band (high pass [HP]), wide-band noise (WB), and clicks at different rates. Materials and Methods: ARTs using different stimuli like PT of frequencies 500, 1 k, 2 k, 4 k Hz, the low-frequency band (LP) (i.e., noise in the frequency range of 125–1600 Hz), the high-frequency band (HP) (i.e., noise in the frequency range of 1600–4000 Hz), wideband noise (WB) (125–4 kHz), and clicks at different click repetition rates as 50/s, 100/s, 150/s, 200/s, 250/s, and 300 clicks/sec was measured on 50 normal-hearing individuals. The ARTs were documented for both ipsilateral and contralateral recording for all test stimuli. Results: The mean ART obtained for 500 Hz PT was between 85 and 95 dB HL, for WB, it was between 80 and 85 dB, and for LP and HP, it was between 75 and 80 dB HL. For click stimulus, a better threshold of 70 dB HL was obtained at 300/s. The mean ART elicited by PT and WB noise was higher than click stimuli. The mean comparison of the ART obtained between PT and WB revealed better thresholds for WB noise. Between WB noise and clicks, better ART was observed for click stimuli. The clicks elicited ART were better than noise stimuli followed by PT. Ipsilateral stimulation yielded better responses than contralateral stimulation for all stimuli. Discussion: The mean ART for click stimulus was better because it stimulated a wider frequency range in cochlea than PT, LP, and HP. Even though WB has a wider frequency range than clicks, the mean ART for click stimulus was much better because of a factor called temporal integration, i.e., stimulation at a higher rate (300/s). Conclusions: The click stimuli at a higher rate can be used effectively to measure ART's for individuals with lower comfortable levels as it can elicit reflex at lower thresholds.