|Year : 2022 | Volume
| Issue : 2 | Page : 126-129
Q10 and Tip Frequencies in Individuals with Normal-Hearing Sensitivity and Sensorineural Hearing Loss
N Devi, K Sreeraj, S Anuroopa, S Ankitha, V Namitha
Department of Audiology, All India Institute of Speech and Hearing, Mysore, Karnataka, India
|Date of Submission||04-Jan-2022|
|Date of Acceptance||11-Mar-2022|
|Date of Web Publication||21-Sep-2022|
Dr. N Devi
Department of Audiology, All India Institute of Speech and Hearing, Manasagangothri, Mysore, Karnataka
Source of Support: None, Conflict of Interest: None
Context: Cochlear plays a major role in providing fine-tuned frequency resolution of the sounds that were perceived. However, in the impaired auditory systems, this frequency resolution is affected, which indirectly leads to distortion in the perception of the sounds. However, the sharpness of tuning of a filter can be obtained from Q10 values and the shift in the tip frequencies of the psychophysical tuning curve can provide an estimate for the frequency resolution of the cochlea. Aim: This study aimed to estimate and compare the Q10 values and tip frequency between individuals with normal hearing and hearing loss. Subjects and Methods: A total of 92 ears were included for the study which was divided into two groups based on the hearing sensitivity. The psychophysical turning curves were obtained for 500 Hz, 1 kHz, 2 kHz, 4 kHz, and 6 kHz. The data on Q10 and the tip frequencies were statistically analyzed. Results: The results reveal that individuals with hearing loss have lesser Q10 values compared to individuals with normal hearing and this increased with increase in the test frequencies. Comparing the shift in the tip frequency between the two groups of individuals, the shift was toward the lower frequency which indicates it is an involvement of the outer hair cells. However, this study was limited only to those with mild flat sensory neural hearing loss. Conclusion: It could be concluded that Q10 and tip frequency measurement would be a valid measure for frequency resolution of the cochlea.
Keywords: Cochlear, filters, frequency resolution, tip frequency
|How to cite this article:|
Devi N, Sreeraj K, Anuroopa S, Ankitha S, Namitha V. Q10 and Tip Frequencies in Individuals with Normal-Hearing Sensitivity and Sensorineural Hearing Loss. Indian J Otol 2022;28:126-9
|How to cite this URL:|
Devi N, Sreeraj K, Anuroopa S, Ankitha S, Namitha V. Q10 and Tip Frequencies in Individuals with Normal-Hearing Sensitivity and Sensorineural Hearing Loss. Indian J Otol [serial online] 2022 [cited 2022 Sep 25];28:126-9. Available from: https://www.indianjotol.org/text.asp?2022/28/2/126/356455
| Introduction|| |
Cochlear hearing impairment is related to complete loss of either inner hair cells (IHCs) or outer hair cells (OHCs). Sometimes, total failure of the function of inner hair cells might be seen over a region of the cochlea; these nonfunctional places of the cochlea are also called “dead regions.” The neurons lying within and adjacent to the dead regions are responsible for the response of a particular series of characteristic frequencies (CFs) of the IHCs. The regions are usually found in moderate-to-severe sensorineural hearing loss. IHCs are called the transducers of the cochlea and convert the vibrations of the basilar membrane into action potential in the auditory nerve. Despite the presence of IHCs, they might be nonfunctional. When the IHCs are impaired in the cochlea, transduction will not take place in that region. Due to the absence of transductions, these regions are called dead region. The dead regions can be characterized regarding the dead place in the cochlea, i.e., either apical dead region or basal dead region. Since IHC damage is usually related to OHC damage, IHCs and neurons, the tuning of the basilar membrane, may be abnormal, even in the areas which are not dead. The dead region is defined regarding the CFs of the IHCs and/or neurons adjacent to the dead region. This characterization seems to be appropriate even if the CFs of the IHCs and neurons are moved from “standard” values. The neurons directly innervating the dead region cannot detect the basilar membrane vibration pattern directly, i.e., if the IHCs of basal end of basilar membrane are impaired which are responsible for the detection for high CFs, but if high-frequency sinusoid is presented and sufficient basilar membrane vibrations are produced at the more apical region, it might lead to downward spread of excitation. The neurons which are tuned for the lower frequencies can detect the high-frequency sound. The opposite of it is also possible via the upward spread of excitation. Due to this factor, there is a possibility that the audiometric threshold at a particular frequency may be lesser than the “true” value of hearing loss. These “dead regions” in the cochlea can be suspected in the individuals with sensorineural hearing loss, but information regarding dead regions cannot be obtained by looking at the audiometric values alone. When there is the existence of dead region, the audiometric values would give a misleading impression of the amount of hearing loss for the tone/s falling in the dead region. Hearing loss in a dead region might be greater during an audiometric evaluation than the 'true' hearing loss. If there is dead region, the absolute thresholds may be elevated in two main ways. Firstly, the active mechanism in the cochlea is impaired, which results in decreased basilar membrane vibration for a given low sound level. Therefore, to achieve the just detectable amount of vibration, the sound level must be greater than the normal level. Secondly, IHC dysfunction can result in decreased effectiveness of transduction, thus a larger amount of basilar membrane vibrations are needed to reach the threshold. The characteristics in the audiogram that can be considered strong indications for the presence of the dead region are as follows: (1) a hearing loss 75–80 dB at low frequencies or >90 dB at high frequencies for high-frequency dead regions. (2) A low-frequency dead region can be expected when there is a hearing loss of 40–50 dB at low frequencies with a near-normal hearing at high and mid-frequencies. (3) Another indication for the low-frequency dead region is hearing the loss of greater than 50 dB at low frequencies comparatively less hearing loss at higher frequencies. (4) A high-frequency dead region is expected when there is a rapid increment of hearing loss (more than 50 dB/octave) with increasing frequency. For detection and diagnosis of dead regions in the cochlea, there are two popular methods, namely masking with threshold-equalizing noise and psychophysical tuning curves (PTCs). PTC is a curve plotting the level of a narrow-band masker needed to mask a fixed sinusoidal signal, as a function of masker frequency. PTC demonstrates the best responses of auditory nerve fibers and hence better thresholds at the fiber CF and at the frequencies immediately surrounding it. These curves are employed to assess the frequency selectivity and dead regions in individuals with hearing loss. The dead regions in cochlea occur due to cochlear hearing loss, but the severity of the dead regions depends on the degree of sensorineural hearing loss. Since the information about the dead regions has certain implications for the perception of pitch, loudness, speech as well as for amplification devices,, PTCs give a more accurate representation of critical bandwidth of basilar membrane than difference limens for frequency as well as better representation of the ear's frequency selectivity. By using PTCs as a measurement of pitch perception, more information about physical properties is known which can be quantified with a figure of PTC slope called Q10 value. Some sharply tuned tips are found in the frequency region of the graph of PTCs, and these tips are identified as the masker frequency which requires least sound pressure level (SPL) in order to mask the probe. For normal-hearing listeners, the tip of the PTC always lies close to the signal frequency. Whereas, for individuals with hearing impairment, the tip gets shifted far away from the signal frequency. If the tip of the curve is shifted away from the signal frequency, then this frequency is detected by an area on the basilar membrane is defined as 'off frequency listening'. There are two explanations for this shift. The first explanation is that “the shift may be due to the fibers which respond to high-level stimulation despite being damaged.” The second explanation is that the change “may be due to the high-threshold fibers which are still intact.” However, functionally both arguments are similar. Another explanation is that the shift is the result of overall level on the traveling wave on the basilar membrane. The evidence proves that with the increasing level, the peak of the traveling wave shifts in a basal direction. However, there is a dearth of information regarding the data of Q10 values and tip frequency in comparison with sensorineural hearing loss. The present study aimed to compare the Q10 and tip frequency in individuals with normal-hearing sensitivity and sensorineural hearing loss.
| Subjects and Methods|| |
The study included 92 ears. The ears were categorized into two groups. Group I comprised 64 (32 left ears and 32 right ears) with normal-hearing sensitivity (32 males and 32 females) within the age range of 18–55 years, with a mean age of 30.5 years, standard deviation (SD) = 10.94. Group II consists of a total of 28 ears with mild flat sensorineural hearing loss (14 males and 14 females) in the age range of 18–55 years, with a mean age of 38.6 years, SD = 9.3. All the participants were explained about the purpose and nature of the study, and written consent was taken individually. This study adhered to the “Ethical guidelines for bio-behavioral research involving human subjects.”
The fast PTC software (SWPTC, version 188.8.131.52) was used to obtain the PTCs using pure tones at 500 Hz, 1 kHz, 2 kHz, 4 kHz, and 6 kHz. The participants were made to sit on a comfortable chair in an air-conditioned sound-treated room. To estimate threshold, the headphones were placed on the participant's ear. The thresholds were estimated using the software itself. For measuring Q10 and tip frequency, the signal duration at each frequency was maintained at 0.2 s, with an interval of 0.2 s between the pulses. The level of the signal was 10 dB SL, which was selected based on the pure-tone thresholds of the participants at the frequencies mentioned above found using the same software. The noise used for masking was swept in a forward sweeping manner with a rate of change of 2 dB/s. The initial noise level for the test was set at 50 dB SPL, and this level was kept constant across all the test frequencies. Further, an additional low pass noise of 200 Hz at 40 dB SPL was delivered during the measurement to prevent this band from providing listening cues, since the individuals in Group I had normal audiometric thresholds at this frequency. At 500 Hz, 1 kHz, 2 kHz, 4 kHz, and 6 kHz, the Q10 values and the tip frequencies were measured, analyzed, and compared between the two groups. Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) software version 17 (SPSS Inc., Chicago, USA).
| Results|| |
The Shapiro–Wilk test of normality was administered. As the normality was not observed, nonparametric test was used. The Wilcoxon signed-rank test was done to compare scores of right and left ears within Group I. The results reveal (P > 0.05) across all the frequencies for Q10 and tip frequencies. Hence, the scores of the ears were combined for further analysis. Descriptive statistics (mean, median, and standard deviation) were analyzed for the measurements of Q10 values and tip frequencies of 500 Hz, 1 kHz, 2 kHz, 4 kHz, and 6 kHz across both the groups. [Table 1] shows the mean, standard deviation, and median values of Q10 and tip frequency across both the groups of participants.
|Table 1: The mean, standard deviation, and median of Q10 and tip frequency across both the groups of participants|
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From [Table 1], it can be inferred that the scores of Q10 are lesser for Group II compared to Group I. The Q10 values of lower frequencies are lesser compared to higher frequencies for both the groups of participants. Mann–Whitney U-test was done to compare the difference between the groups for Q10 and tip frequency of 500 Hz, 1 kHz, 2 kHz, 4 kHz, and 6 kHz. The results reveal a difference in the scores of Q10 values across the two groups. [Table 2] reveals the results of Mann–Whitney U-test comparing the groups across the different frequencies for Q10 and tip frequencies.
|Table 2: Results of Mann–Whitney U-test comparing the groups across the different frequencies for Q10 and tip frequencies|
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The results of [Table 2] reveal that there is a significant difference between the two groups across the entire test frequencies of Q10 and there is also a significant difference across the frequencies of 500 Hz, 1 kHz, and 2 kHz of tip frequencies. [Figure 1] depicts a representative PTC obtained from a participant in Group I at 1 kHz, and [Figure 2] depicts a representative PTC obtained from a participant in Group I at 1 kHz.
|Figure 1: Psychophysical tuning curves for 1 kHz obtained from a participant in Group I|
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|Figure 2: Psychophysical tuning curves for 1 kHz obtained from a participant in Group II|
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| Discussion|| |
The results of the present study reveal that the frequency resolutions are better in individuals with normal hearing compared to individuals with hearing impairment. This indicates that the tuning curves are broader for an individual with hearing loss. Similar results are reported where the sharpness of the tuning of the auditory filters is affected in individuals with hearing impairment. The results of the data were also compared across frequency; the Q10 scores increased with increase in frequency, which indicates that the frequency resolution is better for the higher frequencies compared to the lower frequencies. This could be attributed to the increased density of medial olivocochlear bundle fiber innervations at higher frequencies. Due to these inherent structural asymmetries, the modulatory gain provided by medial olivocochlear fibers to the cochlea is relatively higher toward the basal portion of the basilar membrane. On comparing the results between groups across all the test frequencies for Q10 and tip frequencies, the results revealed that the ears with cochlear pathology have poorer frequency tuning for the perceived stimuli. However, the shifts of the tip frequency are significant only for 500 Hz, 1 kHz, and 2 kHz. On observation, it reveals that the shifts are toward the lower side of the tip frequency for the lower frequency which indicates that OHCs are affected to a greater extent for those individuals with hearing impairment. This shift of the tip frequency is an indicator for the inner or the OHC damage. If the shift of the tip frequency is toward the higher side, the inner hair cells are also damaged.
| Conclusion|| |
The results of these psychophysical tuning measures were significantly different in individuals with an even milder degree of cochlear hearing loss than those of individuals with normal-hearing sensitivity. The scores of Q10 were poorer with elevated tip frequencies of the PTC even if it is flat configuration of hearing loss. Hence, it can be concluded that psychophysical tuning measures of Q10 and tip frequency can be used as a reliable and valid tool for measuring the frequency resolution of the cochlear. However, this study is limited only with a comparison of flat mild sensorineural hearing loss; further studies are required for comparison among the other configuration and degree of hearing loss.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]