An Application of Disyllabic MSTMs for Patients with Presbycusis / 听力学及言语疾病杂志

Objective To analyze the clinical characteristics of patients with presbycusis by using disyllabic mandarin speech test materials (MSTMs).Methods A total of 59 subjects (23 men and 36 women) with presbycusis,from 61 to 84 years old with the average as 71.3±6.7.They were divided into three groups:the mild group (10 subjects),the moderate group (35 subjects)and the severe group (14 subjects)according to the pure tone average (PTA) thresholds at 0.5,1,2 and 4 kHz from the better ear.In addition,11 subjects of elderly persons with normal hearing were used as the control group.All the subjects enrolled in this study could speak Mandarin well in their daily lives.Nine lists of disyllabic mandarin speech test materials were utilized to test speech recognition threshold (SRT) and P-I function for these groups respectively.Results The PTA(51.65±11.98)and SRT (50.98±16.05)from presbycusis group were much higher than the control group(PTA 19.55± 4.55,SRT 18.79± 7.45),while the average slope of the P-I function 2.63％/dB from the presbycusis group was lower than the control group 4.65％/dB (P＜0.01).The SRT of male patients (56.54±17.23) was higher than the females(47.99± 15.63) (P＜0.05).The PTA and SRT in these three groups divided by degrees of hearing loss were higher than the control group obviously.The PTA and SRT had significantly increased as the degree of hearing loss increased.The differences among these groups were significant (P＜0.01).The average slope of P-I function of these three groups divided by degrees of hearing loss (mild group:2.47％/dB,moderate group:2.76％/dB,severe group:2.42％/dB) was smaller than the slopes in the control group which was 4.65 ％/dB (P＜0.01).The average slope of P-I function among these groups had no significant difference (P＞0.05).Conclusion The SRT of patients with presbycusis increased and the SRT of male was higher than the females.The average slope of P-I function decreased and the curve moved to right side and became a gradual curve.As hearing loss became more severe,the SRT rose more apparently.

Comparison of the Performance between the Mandarin Version of HHIE-S and Single Question in the Hearing Screening in Old Adults / 听力学及言语疾病杂志

Objective To compare the performance of Mandarin screening version of hearing handicap inven-tory in elderly (HHIE-S)and the single question of hearing loss in the hearing screening in the old adults.Methods A total of 570 participants,aged from 50~85 years,of native Mandarin speakers were tested with standard pure tone audiometry (PTA),HHIE-S and single questionAre you now having difficulty in hearing?.HHIE-S>8 was taken as an indicator of hearing handicap.Sensitivity,specificity,negative predictive values and positive predic-tive values of both HHIE-S and single question inquiry when 0.5~4 kHz PTA average > 25 dB,>40 dB and >60 dB were compared.Results The prevalence was 83.9% (478)measured by PTA.The prevalence was 55.3%and 52.5% for HHIE-S and positive answer for single question,respectively.The sensitivity of HHIE-S when the participants grouped with 0.5~4 kHz PTA average > 25 dB,>40 dB and > 60 dB was 61%,85% and 96%, respectively,whereas the sensitivity of single question of the above 3 conditions was 58%,81% and 100%,respec-tively.The specificity of HHIE-S decreased with greater hearing loss.It was 72%,88% and 47% respectively for HHIE-S and 75%,61% and 50% for the single question.There was no significant difference either for sensitivity and specificity between the HHIE-S and the single question.Conclusion Both the Mandarin version of HHIE-S and single question are effective in the hearing screening of old adults.Depending on the purpose and availability of resources,one or both of them can be adopted.

Cross-sectional study of hearing loss among freshmen in university / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#The purpose of the present study was to investigate the prevalence of hearing loss by studying the current status of hearing loss, risk factors of hearing loss, exposure level of noise, and everyday habit of hearing in a group of university students, so as to provide information for hearing loss prevention in university students.@*METHOD@#According to the purposive sampling method, 642 freshmen students participated in the study. Pure tone audiometry, and exposure level of noise scale were performed in all participants.@*RESULT@#(1) According to the hearing loss criterion of WHO/PDH97.3, high frequency hearing loss, and noise induced threshold shifts, the hearing loss prevalence was 0.36%, 20.91% and 6.73%, respectively. (2) Multivariant Logistic regression analysis of high-frequency hearing loss indicated that traffic noise exposure and ear infection were risk factor of high frequency hearing loss.@*CONCLUSION@#There is a high prevalence of high frequency hearing loss in university students (20.91%), which was high related with traffic noise exposure and ear infection.

Wide band tympanometry energy reflectance in Chinese infants and children with normal outer and middle ears / 中华耳鼻咽喉头颈外科杂志

<p><b>OBJECTIVE</b>To explore the law of wide band tympanometry energy reflectance (WBTER) in Chinese infants of Han nationality with normal outer and middle ears, and to provide the normal values for the clinical application of WBTER.</p><p><b>METHODS</b>Ninety four infants (170 ears) of Han nationality with normal outer and middle ears evidenced by temporal bone CT, and 226 Hz and 1 000 Hz tympanometry at the ages between three and 48 months (median age: 14 months) were selected and divided into four groups: 3-6 months (32 ears), 7-12 months (53 ears), 13-24 months (46 ears) and 25-48 months (39 ears). WBTER was conducted on these infants, and the basic law of energy reflectance under different frequencies, as well as the influence of age on energy reflectance were analyzed using SPSS 15.0.</p><p><b>RESULTS</b>The normal value of energy reflectance was higher at low frequency, gradually decreased with the increase of frequency, reached the minimum near 4 000 Hz , followed by constantly increased till 8 000 Hz. In the scope of frequency below 1 000 Hz and above 6 350 Hz, the energy reflectance values of infants in the group of 3-6 months were significantly lower than those of infants in other age groups (P < 0.05). In comparison to the group below six months, the groups over six months generally had higher energy reflectance and lower fluctuation.</p><p><b>CONCLUSIONS</b>The pattern of energy reflectance across frequency range for Chinese infants and children was consistent with that of other races reported in foreign countries. The WBTER changes with the growing of age, which tends to be stable after the first six months of birth.</p>

A comparison of 226 Hz and 1 000 Hz tympanometry in diagnosis of infants otitis media effusion / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To provide a clinical reference by comparing the conventional 226 Hz tympanometry with 1000 Hz tympanometry in two groups of young children with otitis media effusion evidenced by CT scan.@*METHOD@#One hundred and seventy-seven young children (226 ears), from 1 to 60 months, with otitis media effusion were involved in this study. They were divided into six groups by age: 0-6 months group, 6-12 months group, 12-18 months group, 18-24 months group, 24-36 months group, 36-60 months group. They were tested with tympanometry of 2 probe-tones of 226 and 1 000 Hz. Type A tympanogram was defined as a normal middle ear function in 226 Hz and single-or double-peak in 1 000 Hz tympanometry. One hundred and fifty-eight normal young children (266 ears) were selected as control group. The results were analysed with Chi square test. Receiver operator characteristic (ROC) analysis was performed to evaluate the two methods.@*RESULT@#In the young children with otitis media effusion, the detection rate of 226 Hz tympanogram in six groups was 21.1%, 35.2%, 46.9%, 42%, 62.5% and 68% respectively, while 94.7%, 98.1%, 96.9%, 91.2%, 95.8% and 88% respectively in 1 000 Hz tympanogram. In the young children with normal middle ear function, the detection rate of 226 Hz tympanogram in six groups was 95.1%, 88.6%, 85.1%, 93.3%, 88.5% and 93.5%, while 87.8%, 94.3%, 89.4%, 95.6%, 94.2% and 97.8% respectively in 1 000 Hz tympanogram. The detection rate was significantly different between 226 and 1 000 Hz tympanogram in the young children under 36-month old.@*CONCLUSION@#A single-or double-peak 1000 Hz tympanometric patterns as normal criteria was a simple way to evaluate young children s' middle ear function. 1 000 Hz tympanometry should be given priority to the children within 36-month old in detection middle ear function,the 226 and 1 000 Hz tympanometry should be done at the same time within 36-60 months old.

Cochlear implant performance evaluation with cortical auditory evoked potential in a group of post-lingually deaf adults / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To investigate the law of auditory remodeling by studying the Cortical Auditory Evoked Potential in a group of post-lingually deaf adults in the early stage of the cochlear implant use.@*METHOD@#Ten post-lingually deaf adults implanted with PULSAR ci 100 of Medel device ranged from 19 to 52 years old with duration of deafness from 3 months to 23 years.were involved. Their P1-N1-P2 responses to /ba/ at around 60-70 dB SPi and open-set speech recognition scores of mono-syllabic words were recorded at 1. 3 and 6 months after the switch-on of cochlear implants.@*RESULT@#Six out of 10 typical waveforms of Pl-N1-P2 were obtained. The other I were with atypical waveforms. The group with atypical waveform was characterized by long duration and early onset of deafness. There was no significant difference regarding either the amplitude or the latency of each peak at the 3 data collection time points. There was significant difference among the 3 data collection time points about the speech recognition scores with the highest score at the 6th month of switch on. There was no significant correlation between the peak of the CAEP and speech recognition score.@*CONCLUSION@#In the first 6 months of cochlear implant use in the post-lingually deaf adults, the duration and the onset age of deafness played important role in respect of the presence and waveform morphology of the CAEPs. It needs at least 6 months for the central auditory system to make use of the audio input from the cochlear implant.

The effects of hearing level on auditory performance in infants with hearing aids / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#The purpose of this study is to investigate the effects of hearing level on auditory performance in infants with hearing aids and provide a clinical database for their hearing and speech habilitation.@*METHOD@#A total of 32 infants with prelingual hearing loss participated in this study, ranging in age at hearing aid fitting from 3 to 34 months with a mean of 16 months. According to their hearing level, they were divided into three groups. Infants in group A were with moderate hearing loss (41-60 dB HL). Infants in group B were with severe hearing loss (61-80 dB HL). Infants in group C were with profound hearing loss (>81 dB HL). The infant-toddler meaningful auditory integration scale (IT-MAIS) was used to evaluate their auditory performance. The evaluation was performed before hearing aid fitting and 1, 3, 6, 9, 12 months after fitting.@*RESULT@#The mean scores of auditory performance showed significant improvements with time of hearing aid use for the three groups of infants (P 0.05). However, significant differences were observed between group A and C at 3, 6, 9, 12 months after fitting (P < 0.05). Significant differences were also shown between group B and C at 1, 3, 6, 9, 12 months after fitting (P < 0.05).@*CONCLUSION@#Auditory performance of infants with prelingual hearing loss developed significantly with the use of hearing aids within the first year after fitting. The degree of hearing loss in infants had significant influence on the development of auditory performance.

Effect of age at cochlear implantation on auditory performance at the early stage after surgery in infants / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To evaluate the auditory performance of infants with cochlear implants at the early stage after surgery, summarize the development of auditory ability, investigate the effect of age at cochlear implantation on auditory performance within the first year after surgery and provide a reference for their habilitation program.@*METHOD@#A total of 272 infants with prelingually profound hearing loss participated in this study, ranging in age at cochlear implantation from 18 to 36 months. The mean age was 21 months with a standard deviation of 7 months. Infants with cochlear implants were divided into three groups according to their age at implantation. Infants in group A were implanted under 18 months of age. Infants in group B were implanted between 18 and 24 months of age. Infants in group C were implanted between 25 and 36 months of age. Categories of auditory performance (CAP) was used to evaluate the auditory performance, which rates auditory abilities in eight categories for a scale of 0 to 7.@*RESULT@#The mean scores of CAP for all infants at each interval were significantly different after implantation. Significant differences were observed in mean scores of CAP among these three groups in 1 and 3 months after switch-on. However there were no significant differences in pre-operation, 6, 9 and 12 months after switch-on.@*CONCLUSION@#There is a significant improvement in auditory performance of infants with prelingually profound hearing loss within the first year after cochlear implantation. The age at cochlear implantation has no critical influence on the development of auditory capabilities at the early stage after surgery. CAP is a practical tool which can be used in clinic in China.

Clinical findings of a group of children with auditory neuropathy spectrum disorder / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#In order to extend the knowledge of auditory neuropathy spectrum disorder (ANSD), the clinical data of a group of infants and young children with this disorder was reported.@*METHOD@#This retrospective study involved 84 cases (151 ears). The subjects aged from 2 months to 6 years old. Descriptive analysis was carried out on case history, audiological and imaging results and the outcome of cochlear implantation.@*RESULT@#There were a variety of case history, including 11 of hyperbilirubinemia, 2 of family history of deafness, 3 of hypoxia, 1 of prematurity, 1 of nuclei basales pathology, 2 of congenital atelencephalia,and 13 of cochlear nerve deficiency (CND). The audiological results varied too. Click ABR ranged from no response at the maximum output level to Wave V thresholds as low as 70 dB nHL. Behavioral thresholds were mild in 1, moderate in 2 and profound in 20. The inner ear MRI were normal in 16 cases, CND in 12 and CND accompanied by periventricular leukomalacia in 1. 5 cases were implanted in the affected ear. The results in 3 were comparable with that of cochlear loss, 1 were less effective than that of cochlear loss, 1 became none user of the device.@*CONCLUSION@#ANSD is a heterogeneous group with a wide variety on case history, audiological and imaging results and the outcome of cochlear implant. Therefore, comprehensive clinical examinations are necessary so that individualized intervention program can be made.

Audiometric configuration distribution of hearing loss in a clinical population / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#Audiometric configuration distribution of hearing loss was analyzed for public policy efforts of hearing loss prevention and rehabilitation.@*METHOD@#According to the archived records of the Clinical Audiology Center of Beijing Tongren Hospital, Capital Medical University, audiometric configuration distribution was analyzed by different type,degree of hearing loss and age factor.@*RESULT@#1. Overall audiometric configuration distribution: the percentages of "sloping", "rising", "flat", "U-shaped", and other type of audiometric configuration distributions are 52.8%, 7.6%, 15.4%, 13.2% and 11.0%, respectively. No difference was found between male and female in the audiometric configuration distribution; 2. Audiometric configuration distribution by type of hearing loss: sloping hearing loss dominants sensorineural and mixed hearing loss; 3. Audiometric configuration distribution by degree of hearing loss: sloping hearing loss dominants mild, moderate and severe hearing loss, U-shaped hearing loss dominants profound hearing loss; 4. Audiometric configuration distribution by age: for age group 5 to 7, the highest prevalence of audiometric configuration is "sloping", followed by "flat", "U-shaped", other type and "rising"; with the age increasing, the percentage of sloping hearing loss increased dramatically.@*CONCLUSION@#Audiometric configuration distribution shows obvious characteristic of on the type, degree of hearing loss and age factor. "sloping" hearing loss dominates the audiometric configuration.

The diagnosis of auditory neuropathy in young children / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To present the clinical data of a group of children with audiological profile of auditory neuropathy.@*METHOD@#Forty-eight infants and young children who had severely abnormal click ABRs along with present CMs and/or DPOAEs were included in this retrospective study. Click ABRs, CMs, DPOAEs, tympanograms, behavioral thresholds and inner ear MRI were analysed.@*RESULT@#Fourty children present with bilateral audiological profile of AN, 8 were unilateral. Most of the ears (68.2%) were of absent click ABRs at the maximum presentation level of 100 dB nHL. However, some of them had repeatable Wave V at very high presentation levels. All ears showed present CMs while only 41.7% showed preserved DPOAEs. Four children were diagnosed as CND by further investigation of inner ear MRI.@*CONCLUSION@#It is recommended that CM testing be carried out routinely in children with severely abnormal click ABRs so as not to miss out AN; Behavioral hearing can not be predicted by auditory evoked responses; if audiological profile of AN is detected, further MRI exploration of well-developed cochlear nerve is necessary.

The characteristics and development of auditory skill for infants with different age after cochlear implantation / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To analyze the characteristics and development of auditory skill for infants with different age before and after cochlear implantation by using infant-toddler meaningful auditory integration scale (IT-MAIS) questionnaire, and provide the useful information for the criteria of candidacy for cochlear implantation in infants and habilitation after cochlear implantation.@*METHOD@#One hundred and thirty-nine prelingually infants with profound hearing loss were included in this study. According to the age at implantation, the infants were divided into 5 groups. They were group A ( 0.05). There were no significant differences in mean scores over time among the 5 groups by Multiple Comparison in ANOVA (P > 0.05). The scores were increased with time and there were significant differences in mean scores among the different time before and after switch-on by Multiple Comparison in ANOVA (P < 0.05) for each group.@*CONCLUSION@#The development of the auditory skill for infants followed the same rate in different gender. The auditory skill for infants after cochlear implantation developed rapidly regardless of age at implantation. Most of infants indicated rapid improvement in auditory skill within the first 6 months after switch-on, and then showed relative slow increase in the following 6 months.

Bone-conducted Auditory Steady-state Responses in Adults with Normal Hearing / 听力学及言语疾病杂志

Objective This paper is to explore the relationship between the placement of the bone oscillator and bone-conducted thresholds to ASSR stimuli in adults with normal hearing and to investigate the amplitude and the threshold differences to bone-conducted auditory steady-state responses (BC-ASSR) stimuli between single - and multiple-stimulus conditions. Methods Two groups of subjects were selected with 0. 5, 1, 2 and 4 kHz brief tones repeated at the rate of 77, 87, 93 and 101 Hz using a B-71 bone oscillator either in single- or multiple ted no significant differences between mastoid and behind-the-ear placements. The mean and standard deviations of bone-conducted behavioral thresholds to ASSR stimuli at 0.5, 1, 2 and 4 kHz were 62.6±4.8,47.1±4.8,46.8cant difference between the two conditions while the mean and standard deviations of BC-ASSR thresholds at 0.5, 1, 2 and 4 kHz were 96.7±9.7,70.3±11.6,60.6±7.4,52.8±7.2 dB re: 1μN (ppe), respectively. Conclusion The behavioral bone-conducted thresholds to ASSR stimuli with mastoid and behind-the-ear placemen yielded no significant differences. When the stimuli intensity was 50 dB nHL, the amplitudes in single-stimulus condition were significantly higher than those to multiple-stimulus condition. There were no significant differences for BC-ASSR thresholds between single- and multiple-stimulus condition.

The phonetic development of normal-hearing pre-school children / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To collect the daily speech materials and to discuss the speech development of normal-hearing pre-school children.@*METHOD@#Based on the database of daily speech materials of children who are 3 to 5 years old, from separate monosyllabic word to syllable,analysis the frequency of words and compare them with adults.@*RESULT@#In the spoken words of children who are 3 to 5 years old, we can find all Mandarin phonemes. With independent sample t test, it was shown that there is no significant difference in the distributing of phonemes between children and adults.@*CONCLUSION@#Children who are 3 years old have developed the phonetic system of the language basically.

The normal values of multiple-frequency tympanometry in normal newborns / 临床耳鼻咽喉头颈外科杂志

OBJECTIVE@#To discuss the multiple-frequency probe tones tympanograms and the normal ranges of admittance, susceptance and conductance in normal newborns.@*METHOD@#Tympanometries with 226 Hz, 678 Hz and 1000 Hz probe tones were obtained from newborn infants with normal TEOAE and DPOAE(55 infants, 110 ears), analysed multiple-frequency prone tones tympanograms and values of admittance, susceptance and conductance by using GSI-33 middle ear analyzer.@*RESULT@#226 Hz tympanograms for admittance, susceptance and conductance main were W-shaped, the percentages were 90.0%, 99.1% and 85.5%. 678 Hz tympanograms for admittance, susceptance and conductance main were single-peaked, the percentages of single-peaked type were 62.7%, 77.3% and 62.7%, and the percentages of W-shaped type were 34.6%, 20.9% and 31.8%, had a little three-peaked type. 1000 Hz tympanograms for admittance, susceptance and conductance main were single-peaked, and percentages were 96.4%, 99.1% and 97.3%, and had a little W-shape type but no three-peaked type. There were significant differences between admittance and susceptance, susceptance and conductance in 226 Hz and 678 Hz probe tones tympanogram. There were significant differences between admittance and susceptance, susceptance and conductance, admittance and conductance in 1000 Hz probe tones tympanogram.@*CONCLUSION@#Multiple-frequency probe tones tympanograms and the normal ranges of admittance, susceptance and conductance of normal newborn infants is obtained, and 1000 Hz probe tone tympanometry is a sensitive test for function of middle ear in newborn infants.

Functional outcomes of cochlear implantation in patients with malformed inner ear / 中国耳鼻咽喉头颈外科

OBJECTIVE The aim was to explore the clinical experiences and access the auditory performance and speech intelligibility of cochlear implantation in patients with inner ear malformations. METHODS Among 700 patients who received multi-channel cochlear implantation from 1997 to 2007 in Beijing Tongren Hospital, 108 patients were diagnosed with malformed inner ear. A retrospective study was performed about the surgical characteristics and the mapping characteristics after implantation. The long term follow-up of the rehabilitative efficacy will also be presented. RESULTS ①All patients restituted auditory after operation. ②After the regular rehabilitation, the long term follow-up of the auditory performance and speech intelligibility were very positive. Everyone has shown improved listening and communication skills evaluated by Categories of Auditory Performance and Speech Intelligibility Rating. ③Most of the children are studying or working and are actively involved in their local communities. CONCLUSION The cochlear implantation can be performed safely in patients with malformed inner ear. The results suggest that cochlear implantation could also provides long-term benefits to those malformed inner ear cases.

Research on Auditory Steady-state Responses to Multiple Simultaneous Stimuli of Normal-hearing Adults / 听力学及言语疾病杂志

Objective To explore some characters of auditory steady-state responses (ASSR) to multiple simultaneous stimuli in a sample of normal-hearing adults.Methods The ASSR to multiple simultaneous stimuli were recorded in a sample of 32 normal-hearing adults (64 ears). Simultaneous carrier tones (0.5, 1, 2 and 4 kHz), modulated in amplitude at different rate of 77, 85,93, 101 Hz for left ear and 79, 87, 95, 103 Hz for right ear, were presented binaurally by the insert phones. For each subject the response thresholds (RTHs) at 0.5, 1, 2 and 4 kHz were determined automatically and compared with the corresponding behavioral thresholds (BTHs).Results ①In the normal-hearing adults, RTHs were on average between 7～19 dB above the BTHs.②2-way repeated measures ANOVA (ear?carrier frequencies) showed significant main effect between carrier frequencies on RTH ( F =31.254; ? 3,179; P =0.000). Post Hoc analysis indicated that this effect was due to the highest threshold found at 0.5 kHz. The test showed no significant difference of threshold between left ear and right ear ( F =1.942; ? 1,179; P =0.165). ③Taking 60 dB SPL as analysis level, 2-way repeated measures ANOVA (gender?carrier frequencies) revealed significant difference of amplitude between male and female( F =16.490; ? 1,175; P =0.000); and difference of amplitude between carrier frequencies ( F =2.948; ?3, 175; P =0.034).④The average testing time was 61 minutes for male and 69 minutes for female. Independent t-test showed statistical significance within sex.⑤Two- way ANOVA (state?frequency)showed that background EEG noise were significantly higher in awake than that in sleep ( F =152.511; P =0.000). There were no appreciable significance in background noise among frequencies. Conclusion The ASSR to multiple simultaneous stimuli was proven to be a frequency specific, objective and valid technique for threshold estimation at least for normal-hearing adults. Issues concern ing clinical use were discussed.

Artifactual Responses when Recording Auditory Steady-State Responses to Bone-Conduction Stimuli / 听力学及言语疾病杂志

Objective To explore artifactual responses of auditory steady-state reponses (ASSRs) to bone-conduction stimuli.Methods The present study involved a group of subjects,aged between 5 to 39 months,with bilateral profound sensorineural hearing losse.Recorded were the reponses to multiple bone-conducted 0.5,1,2,4 kHz tone pips repeated at the rates of 77～101 Hz.All the subjects were sedated by Hydrate Chloride during the testing.Results Artifactual ASSRs were seen at 115 and 100.5 dB (re:1?N) (The above levels are equivalent to around 60 dB HL) at 1 and 4 kHz.No artifactual responses were recorded at 0.5 and 2 kHz stimuli at the maximum output level.Conclusion Bone-conducted hearing loss greater than moderate can not be tested reliablely due to artifactual responses and lower maximum output level than that of air conduction.