ORIGINAL ARTICLE
Year : 2022 | Volume
: 6 | Issue : 1 | Page : 6--11
Comparison of acoustic reflex thresholds across different stimuli
Neelamegarajan Devi1, Ajithkumar Murugesan2,
1 Department of Audiology, All India Institute of Speech and Hearing, Mysuru, Karnataka, India
2 All India Institute of Speech and Hearing, Mysuru OSC, Sub-divisional Taluk Hospital, Sagara, Karnataka, India
Correspondence Address:
Dr. Neelamegarajan Devi
Department of Audiology, All India Institute of Speech and Hearing, Mysuru, Karnataka
India
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.
How to cite this article:
Devi N, Murugesan A. Comparison of acoustic reflex thresholds across different stimuli.Ann Indian Acad Otorhinolaryngol Head Neck Surg 2022;6:6-11
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How to cite this URL:
Devi N, Murugesan A. Comparison of acoustic reflex thresholds across different stimuli. Ann Indian Acad Otorhinolaryngol Head Neck Surg [serial online] 2022 [cited 2023 Mar 25 ];6:6-11
Available from: https://www.aiaohns.in/text.asp?2022/6/1/6/358576 |
Full Text
Introduction
The middle ear comprises of stapedius muscle and tensor tympani muscle. These muscles' activity can be examined indirectly by tracking air pressure changes in the ear canal reaction to intense noise.[1] The acoustic reflex (AR) is “the amount of middle ear muscle contraction in reaction to intense acoustic stimulation.” It is also defined as a “bilateral reflex (the reflex occurs in both ears with single ear stimulation) and be measured by recording the change in acoustic impedance and admittance, in response to stimuli to the same ear or opposite ear called the uncrossed and crossed reflex respectively.[2] The neural mechanism mediates these ARs. With a high-intensity auditory stimulus, the sensory part of the AR goes from the stimulated cochlea via the auditory nerve to the ipsilateral ventral cochlear nucleus (VCN). The second-order neuron from the VCN passes through the trapezoid body leading to two ipsilateral and contralateral pathways. One ipsilateral pathway goes from the VCN to the ipsilateral facial nerve nucleus. The motor neuron of the facial nerve proceeds to the stapedius muscle on the same side as the stimulated cochlea. The second uncrossed pathway goes from the VCN to the ipsilateral superior olivary complex (SOC). The third-order neurons proceed to the ipsilateral facial nerve nucleus, from which motor neurons of CN VII activate the ipsilateral stapedius muscle. One of the contralateral AR pathways goes from the ipsilateral VCN to the ipsilateral SOC, from which third-order neurons cross to the contralateral facial nerve nucleus. In the second crossed pathway, neurons from the ipsilateral VCN cross the contralateral SOC, sending third-order neurons to the contralateral facial nerve nucleus. For both contralateral pathways, the motor legs of the reflex arc go from the contralateral facial nerve nucleus via CN VII to the stapedius muscle in the ear opposite to the stimulated cochlea.[3]
The lowest intensity level at which an AR is elicited for different stimulus for each ear is called the AR threshold (ART).[4] The AR can be measured in terms of ipsilateral and contralateral ARs. Comparatively, the less intensive sound is required for eliciting ipsilateral reflex than for contralateral reflex.[5] The ARTs can be elicited by acoustic stimuli such as pure tone (PT), broadband noise, and click sounds. The ART's were found to vary from 85 to 100 dB SPL while using PT stimuli from 250 to 4000 Hz. The reflex threshold improved by 20 dB when elicited by broadband noise stimulus.[6] At varying click rates, the threshold benefit (thresholds of the AR decreased when the repetition rates of click stimulus increased) was 11.2 dB with a rate increased from 50 to 100/s, 7.8 dB with a rate rise from 100 to 200/s and further decreased for 200–300/s to 2.6 dB indicating significant improvement in threshold with an increase in click rate.[7] To find the effect of aging on ART using different click rates, older adults reported having decreased rate integration, which indicates that older adults demonstrated more deficient processing for the faster rate of stimuli in the auditory reflex pathway.[8] ART was spread around 72.7 dB SPL for white noise, and the threshold was around 73.9 dB SPL for click stimulus at a repetition rate of 128/s, but the threshold produced by click reflexes was well defined than those produced by white noise.[9] However, very few research studies in the literature have made an effort to compare the threshold difference between PT evoked and clicks evoked ART's.
In individuals with normal hearing, a significant increase in AR amplitude was found at different click rates from 0 dB SL to 12 dB SL, and it was significant only from 100/s 200/s. ART had a mean improvement of 15.43 dB while increasing the click rate from 50 to 300/s in children with normal hearing and 7.34 dB in children with sensorineural hearing loss, attributing better temporal integration with normal hearing than children with sensorineural hearing loss.[10] When ART using noise and PT is compared, 20 dB of additional stimulation energy was utilized to respond for PT rather than noise.[11] There is a dearth in the literature comparing the ARTs elicited by PT, the low-frequency band (low pass [LP]) and high-frequency band (high pass [HP]), wideband noise (WB), and clicks at different rates, which will be of great clinical utility in difficult-to-test populations like individuals with hyperacusis, reduced comfort level, recruitment, and also for children.
Materials and Methods
Subjects
Fifty participants (25 males and 25 females) within the age range of 18–50 years (mean age of 22.76 ± 3.66 years in males and 23.84 ± 3.82 in females) participated. Written consent was taken from all participants. Participants were selected based on normal hearing sensitivity, normal tympanometry findings, and no known history of external or middle ear problems and neurogenic abnormalities. All the subjects had auditory sensitivity within 15 dB HL in the frequency range of 0.25 and 8 kHz. And the yielded normal tympanometry results at the time of testing. Their static admittance results for the 226-Hz probe tone ranged from 0.3 to 1.4 ml with the presence of ARs at 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz PT frequencies and otoacoustic emissions.
Methods
The equipment used was a two-channel diagnostic audiometer from Grason–Stadler company (GSI-61), which was coupled with a TDH 39 headphones and B-71 bone vibrator for estimating the hearing sensitivity calibrated middle ear analyzer GSItympstar version 2 for tympanometry and reflectometry and otoacoustic measurements were carried out using ILOV 6 equipment. All the participants were subjected to tests in an acoustically treated room, meeting the ambient noise level criteria.[12] Stimuli used for ART measurement were 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 (WB) (125–4 kHz), and clicks (frequency spectrum of click stimuli ranged from 50 to 4 kHz for ipsilateral stimulation and 50–3.6 kHz for contralateral stimulation) at different click repetition rates as 50/s, 100/s, 150/s, 200/s, 250/s, and 300 clicks/s, where all these stimuli are inbuilt or default stimulus available in GSI-tympstar version 2.
Ethical consideration
The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional guidelines on human experimentation. These guidelines adhered to the standards of the Helsinki Declaration.[13]
Procedure
The ART was estimated using 500, 1000, 2000, and 4000 Hz tonal stimuli for both ipsilateral and contralateral recordings. Similarly, ART thresholds using the low-frequency band (LP), the high-frequency band (HP), wideband noise (WB), and click stimuli at different rates such as 50/s, 100/s, 150/s, 200/s, 250/s, and 300 clicks/s was estimated for both ipsilateral and contralateral recordings using regular AR measurement paradigm. The initial presentation was 50 dB peSPL. Until the reflex threshold is obtained, the intensity level was increased by 2 dB. The stimulus presentation was repeated at 2 dB lower levels to ensure the absence of reflex until the change in AR amplitude was more significant than 0.03 ml. Out of these, the rate and the stimulus at which the maximum number of participants elicited the minimum ART were noted to analyze the data further.
Analyses
The raw data obtained were tabulated and analyzed using SPSS v20 software (released 2011; IBM Corp., Armonk, NY, USA) with appropriate statistical analysis. The normality of the present study's data was found using the Shapiro–Wilk test and Kolmogorov–Smirnov.
Results
The present study was conducted to estimate and correlate the ART for clicks at different rates, LP, HP, wideband noise, and PT in individuals with normal hearing. Shapiro Wilk's test of normality was done to analyze the normality of the data, and this study's data were found to be nonnormally distributed (P < 0.05). Hence, nonparametric inferential statistics were carried out for further analysis. The results are explained under the following headings:
Comparison of acoustic reflex thresholds between gender for all the test stimuli
Mann–Whitney test was carried out to identify the effect of gender on ART. No significant difference was observed (P > 0.05) between males and females. For ART measured values for all the stimulus parameters, male and female data were combined for further analysis. However, the mean, median, and standard deviation (SD) across all the test stimuli for male and female participants are [Supplementary Table 1]. The results of the Mann–Whitney test between the gender across all the test stimuli are provided in [Supplementary Table 2].[INLINE:1][INLINE:2]
Comparison of acoustic reflex thresholds between right and the left ear for the entire test stimulus
The ART elicited for all the stimuli were compared between right and left ears using the Wilcoxon Signed-Rank test. There was a significant difference (P < 0.05) between the right and the left ear for the test stimuli of contralateral 500 Hz PT, ipsilateral WB noise, and all ipsilateral stimulation of clicks at 50/s, 100/s, 150/s, 200/s, 250/s, and 300/s. Hence, further data analysis was done separately for the ears since some stimuli have ear differences. The mean and SD thresholds of AR for the entire test stimulus for the right ear and left ear are depicted in [Figure 1] and [Figure 2].{Figure 1}{Figure 2}
From [Figure 1] and [Figure 2], it was evident that the ART's elicited by PT stimulus was better at 500 Hz than other frequencies, i.e., 86.2 dB HL, 85.4 dB HL for right and left ipsilateral stimulation, and 94.6 dB HL, 92.7 dB HL for right and left contralateral stimulation respectively. For ART elicited by click stimulus, a better threshold was obtained at 300/s rate, i.e., 68.7 dB HL, 66.0 dB HL for right and left ipsilateral and 75.6 dB HL, 75.5 dB HL for right and left contralateral stimulation, respectively. When ARTs are elicited by LP, the thresholds were 82 dB HL, 85 dB HL, 80.8 dB HL, and 86.8 dB HL for right ipsilateral LP, right contralateral LP, left ipsilateral LP and left contralateral LP, respectively. When ART's are elicited by HP, the thresholds were 85.4 dB HL, 91.2 dB HL, 85 dB HL, and 91.2 dB HL for right ipsilateral HP, right contralateral HP, left ipsilateral HP, and left contralateral HP, respectively. Better thresholds were observed LP compared to HP. When ARTs elicited by WB, LP, and HP are compared, a better threshold is observed for WB as it covers a wide frequency range from 125 Hz to 4KHz. Compared ARTs elicited by PT with LP and HP, better thresholds were observed for LP and HP. The thresholds obtained for the ART elicited by WB noise stimuli were 80.8 dB HL and 79.2 dB HL for ipsilateral stimulation at the right and left ear, respectively. The thresholds obtained for the contralateral stimulation are 82.9 dB HL and 99.2 dB HL at the right and left ear, respectively. It was also observed that PT of 500 Hz and 1000 Hz had better thresholds; WB had better thresholds than LP and HP. Hence it was taken for further analysis to find a difference in thresholds concerning other stimuli.
Mean thresholds revealed that ART elicited by PT and WB noise was higher than click stimuli. The mean comparison of the ART obtained between PT and WB noise revealed better thresholds for wideband noise stimuli. Between WB noise and clicks, better ART was observed for click stimuli. Ipsilateral stimulation yielded better responses than contralateral stimulation for all stimuli. Equating the ART elicited by click stimulus at different rates, better ART was observed as the rate of clicks increased in both ipsilateral and contralateral stimulation, i.e., 84.5 dB HL to 68.74 dB HL at right ipsilateral 50/s to 300/s stimulation respectively, 89.6 dB HL to 75.6 dB HL at right contralateral 50/s to 300/s stimulation respectively, 83 dB HL to 66 dB HL at left ipsilateral 50/s to 300/s stimulation respectively, and 89.9 dB HL to 75.7 dB HL at left contralateral 50/s to 300/s stimulation respectively. [Figure 3] depicts the ART across different click rates obtained on both ears for ipsilateral and contralateral stimulation.{Figure 3}
[Figure 3] shows that for click stimulus, the highest threshold was obtained at 50/s, and a drastic improvement in threshold was seen when the click rate was increased to 150/s due to temporal integration. There was further improvement in thresholds for further increase in click rates such as 200/s, 250/s, and 300/s, but it was observed to be a minimal improvement. On the whole, at 300/s, a better threshold was obtained, so it was taken to compare with the other two stimuli. Threshold differences of 17.46 dB HL were obtained between right ipsilateral PT 500 Hz and click at 300/s; 5.4 dB HL between right ipsilateral WB noise and PT 500 Hz; 12.06 dB HL between right ipsilateral clicks at 300/s and WB noise; 19.38 dB HL between left ipsilateral PT 500 Hz and clicks at 300/s; 6.2 dB HL between left ipsilateral WB noise and PT 500 Hz; 13.18 dB HL between left ipsilateral clicks at 300/s and WB noise; 19 dB HL between right contralateral PT 500 Hz and clicks at 300/s; 11.7 dB HL between right contralateral WB noise and PT 500 Hz; 7.3 dB HL between right contralateral clicks at 300/s and WB noise; 17.12 dB HL between left contralateral PT 500 Hz and clicks at 300/s; −6.58 dB HL between left contralateral WB noise and PT 500 Hz (average of wideband noise is more than PT average); 23.7 dB HL between left contralateral clicks at 300/s and WB noise.
As depicted in [Table 1], threshold differences of 20.16 dB HL were obtained between right ipsilateral PT 1 KHz and click at 300/s; 8.1 dB HL between right ipsilateral WB noise and PT 1 KHz; 22.48 dB HL between left ipsilateral PT 1 kHz and clicks at 300/s; 9.3 dB HL between left ipsilateral WB noise and PT 1 kHz; 22.2 dB HL between right contralateral PT 1 kHz and clicks at 300/s; 14.9 dB HL between right contralateral WB noise and PT 1 kHz; 39.82 dB HL between left contralateral PT 1 kHz and clicks at 300/s; 16.12 dB HL between left contralateral WB noise and PT 500 Hz. Thus, by comparing the ART's elicited by different stimuli, clicks stimulus elicited better thresholds than PT and WB noise.{Table 1}
Comparison of the difference in thresholds between pure tones at 500, 1000, 2000, and 4000 Hz (ipsilateral and contralateral) and acoustic reflex using clicks at different rates, and low pass, high pass, and wideband noise
A nonparametric Friedman test of differences among repeated measures was carried out to compare the ear's ART thresholds for both contralateral and ipsilateral stimulation on both the ears separately. The results of the test for comparison of right ear ipsilateral stimulation revealed (χ2[12] = 512.77, P < 0.001) and right ear contralateral stimulation revealed (χ2[12] = 504.19, P < 0.001). Wilcoxon signed-rank test was administered to obtain pairwise comparison. The results revealed a significant difference (P < 0.05) among all the test stimuli pairs compared with the right ear ipsilateral and contralateral stimulation results. The results of the test for comparison of left ear ipsilateral stimulation revealed (χ2[12] = 506.98, P < 0.001) and left ear contralateral stimulation revealed (χ2[12] = 503.97, P < 0.001). To obtain a pairwise comparison, the Wilcoxon signed-rank test results revealed a significant difference (P < 0.05) among all the pairs of test stimuli compared with left ear ipsilateral and contralateral stimulation results.
Spearman's rho coefficient correlation (rs) was carried out to find ART correlation between different stimuli. Results revealed a significant moderate to a strong positive correlation between all the right and left ear stimuli for ipsilateral and contralateral responses across all test frequencies.
Discussion
The ART, a physiological test, is a good measurement in diagnosing hearing disorders in diagnostic audiology. The present study aimed at estimating ART using click stimulus at different rates on fifty normal hearing individuals. The ARTs elicited by PT, clicks, the low-frequency band (LP), the high-frequency band (HP), and wideband noise (WB) were compared.
Comparison of ARTs elicited by different stimuli
The present study results revealed that ART obtained for WB noise was better than PT stimuli. It has also been reported that ART elicited by PT was approximately 15 dB higher than the other stimuli.[14] Margolis and Popelka[15] Comparing WB noise to PT stimuli, a 5 dB better threshold was obtained for WB noise. Comparing wideband noise and click stimuli, the present study found comparatively better ART to click as the ART elicited by click stimuli are well defined than white noise.[9] Comparing ARTs elicited by the LP and HP, better thresholds were observed for LP by 4–5 dB HL. While comparing WB noise with LP and HP, better thresholds were observed for WB by 5–10 dB HL. Better ARTs were found for LP and HP than PT by 5–10 dB HL.
Relationship between different click rates and acoustic reflex thresholds
The present study's results revealed that the ARTs decreased when click rates increased from 50/s to 300/s, i.e., 84.5–68.74 dB HL at right ipsilateral 50/s to 300/s, 89.6–75.6 dB HL at right contralateral 50/s to 300/s stimulation, 83–66 dB HL at left ipsilateral 50/s to 300/s, and 89.9–75.7 dB HL at left contralateral 50/s to 300/s, respectively, which is in accord with the previous studies[5],[13] which concluded that threshold benefit was 11.2 dB with a rate rise from 50 to 100/s, 7.8 dB with a rate rise from 100 to 200/s and further decreased for 200–300/s to 2.6 dB which is attributed to temporal integration. Fielding and Rawool.[14] The ipsilateral ART was reported in children with 10.5 dB improvement in the left and right ears with clicks from 50/s to 100/s.[16] It has also been reported that there is a mean improvement of 7.6 dB, 4.16 dB, 2 dB, and 1.6 dB as rates increased from 50 to 100/s, 100–150/s, 150–200/s, and 200–300/s, respectively, in normal-hearing children[10] which is in accordance to the present study.
Comparison of acoustic reflex thresholds elicited by ipsilateral and contralateral stimulation
ART obtained for all the stimuli in the present study was better in ipsilateral stimulation than contra-lateral stimulation, such as 5–10 dB difference for PT and wideband noise stimuli and 7–12 dB difference for click stimuli. These results are in accordance with the earlier studies where it was concluded that an 11.42 dB betterment in ART for ipsilateral stimulation compared to contralateral stimulation.[17] However, the present study's results disagree with Laukli and Mair[18] reported on 20 normal-hearing adults, which found no significant difference between ipsilateral and contralateral stimulated ART. The present study's comparison of ARTs between genders revealed no significant difference.[19],[20]
Conclusions
ARTs are better when elicited by LP than HP, better than PT. ART of WB noise was better than PT, LP, and HP. ART obtained by clicks was better than WB noise, PT. Comparing all the stimuli, clicks were found to yield a better threshold. This might be due to the stimulation of a wide frequency range and more energy than other stimuli. The ARTs decreased from 50/s to 300/s. The ART's obtained for all the present study stimuli were better in ipsilateral stimulation than contralateral stimulation. A significant difference was not found in comparing the ART's between genders, revealing the absence of gender impact on ART's.
Implications of the study
The ideal rate of clicks, such as 300 clicks/s, can be used to evaluate ART effectively in the clinical population. Moreover, it can be used to measure ARTs in individuals with hyperacusis, individuals with lower comfortable levels, and with recruitment. It can also be used as a screening tool for difficult-to-test population, as it is less time-consuming.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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