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Background and Aim: Hearing sensitivity is so vital for musicians as loud music can cause hearing loss. The aim of this study was to assess hearing sensitivity of musicians in order to determine the effects of music exposure on hearing organ.
Materials and Methods: This case-control study  was conducted on 15 string musicians with musicianship history of more than 10 years and 15 normal hearing subjects. They all were male and 20-30 years old. TEOAEs and DPOAEs performed after otoscopy , immittance and pure tone audiometry in octave frequencies between 250 to 16000 Hz.
Results: There is not significant difference between pure tone thresholds of two groups for all frequencies.A significant difference of TEOAE is found between two groups for total response and amplituds of TEOAEs . DPOAEs amplituds are not significantly different between two groups .
Conclusion: Musicianship may  affect TEOAEs amplitudes , but cannot affect results of PTA and DPOAEs. Therefore this can be useful to detect cochlear lesions secondary to music exposure and also as a tool in hearing protection program.

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Background and Aim: One of the most significant complaints of children with learning disability (LD) is difficulty in understanding speech in the presence of background noise. Different studies have shown that the medial olivocochlear bundle(MOCB) may play a role in hearing in noise. The MOCB function can be evaluated by the contralateral suppression of tone burst evoked otoacoustic emissions (TBEOAEs).The aim of the present study was to evaluate frequency specifications of MOCB by the contralateral suppression of TBEOAEs at 1,2,3 and 4 KHz in response to contralateral white noise in LD students.
Materials and Methods: This case-control study was conducted on 34 LD students aged 7-11 years and 31 normal students matched for age.The contralateral suppression of TBEOAEs was evaluated by comparing TBEOAEs amplitudes with and without contralateral white noise.
Results: In the absence of noise there was no significant difference between TBEOAEs amplitudes of two groups. In the presence of noise significant decrease was seen in TBEOAEs amplitudes at 1,2,3 and 4 KHz in both groups. In LD students the amount of this decrement at 1,2 and 4 KHz was lower than in the normal students.
Conclusion: A significant diminished suppression effect at 1,2 and 4 KHz in LD students indicates that at these frequency regions MOCB function was reduced. Therefore its suggested that the assessment of MOCB by evaluating the suppression effect of TBEOAEs included in the test battery approach used in the diagnostic of LD students.

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Background and Aim: Learning disability(LD) is one of the most prevalent problems among elementary school children. Approximately 10 percent of all elementary school children suffer from this problem. It has been determined that learning disability is predominantly accompanied with subtle impairment in central auditory nervous system. The main idea of this study was to evaluate middle latency auditory evoked potential (MLAEPs) in learning disabled children.

Materials and Method: This cross-sectional study investigated middle latency auditory evoked potential in children with learning disability (n = 31) compared to normal children (n = 31). Latencies and amplitudes of MLAEPs results with different stimulus intensity and binaural stimulation were compared between two groups.

Results: Compared to control group, learning disabled children exhibited smaller amplitudes for all the components except the right ear Na and Pa. There is no significant difference between two groups for latencies of the components.

Conclusion: It seems that middle latency auditory evoked potential may be useful in diagnosis and evaluation of learning disabled children although more investigation is required.

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Background and Aim: Regions in the cochlea with no (or very few) functioning inner hair cells and/or neurons are called dead regions. The aim of this study was to identify the cochlear dead regions in moderate to profound sensory neural hearing impaired children through the Threshold equalizing noise (TEN_HL) test.
Materials and Methods: In this cross-sectional study, the TEN(HL) was performed for the all frequencies available on test CD, on 30 children with ages ranging from five to forteen years (mean age, 8.5 ±2.8 years old).
Results: In this study, 58.3% of ears were found to have a dead region for at least one frequency. Classifying by test frequencies, 20% were found to have a dead region, 24% to be inconclusive and 56% to have no dead regions. The difference between mean SNR(T) in ears with and without dead regions was statistically significant. The difference between mean absolute thresholds in two groups was statistically significant at 1000 Hz and below (p <0.05).
Conclusion: The results indicated a relatively high prevalence of dead regions in children with sensory neural hearing impairment, especially for frequencies at which the hearing loss exceeds 70 dB HL.

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Background and Aim: Hearing protectors (HP)  are widely employed as the only measure against noise exposure.  However, it is well known that unless do workers wear HP continuously, its efficacy will be very low. The purpose of this study was to determine the influence of risk perception, knowledge and safety attitude on hearing protection use in petrochemical industry&aposs workers.
Materials and Methods: In this cross-sectional study a structural questionnaire was administrated to 236 randomly selected workers in Iranian petrochemical industry who had been to 85 dBA noise and some influencing factors including risk perception, knowledge and general attitude to safety on using of HP had been investigated.
Results: This study showed that only 20.3% of employees claimed to wear hearing protection all the time when they exposed to noise. There was a significant relationship between use of hearing protector and worker&aposs risk perception (p=0.048) and also their knowledge about hearing protection(p=0.009). Also, the relationship between general attitude of workers to safety and risk perception was statistically significant (p=0.046).  
Conclusion: The results of the study  showed that for promoting the use of  hearing  protectors,  two main strategy should be followed. First, removing the barriers to make hearing protectors compliant, and  second enhancing the  workers&apos risk perception about hearing loss and  proper use of ear protectors.

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Background and Aim: Tinnitus is an unpleasant sound which can cause some behavioral disorders. According to evidence the origin of tinnitus is not only in peripheral but also in central auditory system. So evaluation of central auditory system function is necessary. In this study Auditory brainstem responses (ABR) were compared in noise induced tinnitus and non-tinnitus control subjects.
Materials and Methods: This cross-sectional, descriptive and analytic study is conducted in 60 cases in two groups including of 30 noise induced tinnitus and 30 non-tinnitus control subjects. ABRs were recorded ipsilateraly and contralateraly and their latencies and amplitudes were analyzed.
Results: Mean interpeak latencies of III-V (p= 0.022), I-V (p=0.033) in ipsilatral electrode array and mean absolute latencies of IV (p=0.015) and V (p=0.048) in contralatral electrode array were significantly increased in noise induced tinnitus group relative to control group.
Conclusion: It can be concluded from that there are some decrease in neural transmission time in brainstem and there are some sign of involvement of medial nuclei in olivery complex in addition to lateral lemniscus.

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Background and Aim: Balance disturbance is one of the non-auditory effects of noisy industrial environments that is usually neglected. The aim of the current study was to investigate the effect of occupational noise on vestibular system among workers with noise-induced hearing loss (NIHL), based on both vestibular evoked myogenic potentials (VEMP) and caloric tests.

Methods: Thirty male workers with noise-induced hearing loss and thirty male matched controls were examined by VEMP and caloric tests. Study parameters included unilateral weakness, p13 and n23 latencies, and p13-n23 amplitude. Caloric test was performed only for 20 patients.

Results: No significant difference was observed in unilateral weakness between the two groups. On the other hand, the difference in mean latencies of p13 in the right ear (p=0.003) and left ear (p=0.01) was significant between the two groups. However, the difference in n23 latency was significant only in the right ear (p=0.03). There was no significant difference between groups in p13-n23 amplitude.

Conclusion: It seems that pars inferior of vestibule is the susceptible part in individuals with NIHL. In general, abnormal findings in both VEMP and caloric tests were more common compared to functional symptoms such as vertigo, which may be due to central compensation and the symmetry of the disorder.

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Background and Aim: Main feature of auditory processing abilities is temporal processing including temporal resolution, temporal ordering, temporal integration and temporal masking. Many studies have shown the superiority of musicians in temporal discrimination over non-musicians. In this study we compared temporal processing in musicians and non-musician controls via Gap in Noise (GIN) test.
Methods: This cohort study was conducted on 24 musicians with mean age of 25.3 years and 24 normal hearing non-musician controls with mean age of 24.5 years, in Faculty of Rehabilitation of Tehran University of Medical Sciences. GIN test results (approximate threshold and percent of corrected answers) obtained and analyzed by Mann-Whitney non-parametric statistical test.
Results: There was significant difference between approximate threshold and percent of corrected answers between musicians and non-musician group (p<0.001), while no sex difference was observed between both groups (p>0.05).
Conclusion: the lower approximate threshold and the more corrected answers in GIN test by musician group indicate rapid auditory temporal processing ability of this group rather than non-musicians group. This might be related to effects of musical training on central auditory processing.

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Background and Aim: Learning disability is a term referes to a group of disorders manifesting listening, reading, writing, or mathematical problems. These children mostly have attention difficulties in classroom that leads to many learning problems. In this study we aimed to compare the auditory attention of 7 to 9 year old children with learning disability to non- learning disability age matched normal group.
Methods: Twenty seven male 7 to 9 year old students with learning disability and 27 age and sex matched normal conrols were selected with unprobable simple sampling. 27 In order to evaluate auditory selective and divided attention, Farsi versions of speech in noise and dichotic digit test were used respectively.
Results: Comparison of mean scores of Farsi versions of speech in noise in both ears of 7 and 8 year-old students in two groups indicated no significant difference (p>0.05) Mean scores of 9 year old controls was significant more than those of the cases only in the right ear (p=0.033). However, no significant difference was observed between mean scores of dichotic digit test assessing the right ear of 9 year-old learning disability and non learning disability students (p>0.05). Moreover, mean scores of 7 and 8 year- old students with learning disability was less than those of their normal peers in the left ear (p>0.05).
Conclusion: Selective auditory attention is not affected in the optimal signal to noise ratio, while divided attention seems to be affected by maturity delay of auditory system or central auditory system disorders.

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Background and Aim: N-acetylcysteine, a glutathione precursor and reactive oxygen species scavenger, is reported to be effective in reducing noise-induced hearing loss. Many workers in industry are exposed simultaneously to noise and chemical pollutants such as carbon monoxide. We investigated effectiveness of N-acetylcysteine in protecting the cochlea from simultaneous noise and carbon monoxide damages.
Methods: Twelve rabbits were exposed simeltaneously to 100 dB sound pressure level of broad band noise and carbon monoxide 8 hours a day for 5 days. One hour before exposure, experimental group received 325 mg/kg of N-acetylcysteine while normal saline was administered for the control group. The protective effect of N-acetylcysteine was evaluated 3 weeks after exposure by histological assessment of the hair cells.
Results: Simultaneous exposure to noise and carbon monoxide resulted in a considerable damage to the outer hair cells however, the inner hair cells and the pillar cells remained intact. Use of N-acetylcysteine in the experimental group significantly reduced the extent of outer hair cell loss.
Conclusion: N-acetylcysteine attenuates simultaneous noise and carbon monoxide induced hair cell damage in rabbits.
Ke

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Background and Aim: One of the chemical pollutions which is frequently common in industry-other than noise is carbon monoxide. The present study aimed to assess the putative protective effect of N-acetylcysteine on the function of outer hair cells of rabbits exposed simultaneously to noise and carbon monoxide.
Methods: 24 male rabbits are entered in this interventional study. After obtaining baseline distortion product otoacoustic emissions, rabits were randomely devided into four groups. The groups Included: exposed with noise and received saline, exposed with noise and carbon monoxide and received saline, exposed with noise and received N-acetylcysteine, and exposed with noise and carbon monoxide and received N-acetylcysteine. Subsequently, they were evaluated again with distortion product otoacoustic emissions in two stages (two hours and one week after the exposure). Data were recorded and analyzed using paired and independent sample t-tests.
Results: Exposure to noise, and also simultaneous exposure to noise and carbon monoxide, and moreover using N-acetylcysteine in both groups, produced significant changes in distortion product otoacoustic emissions amplitudes (p<0.005).
Conclusion: The findings of the present research reveal that simultaneous exposure to noise and carbon monoxide may potentiate noise induced hearing loss. In addition, utilizing N-acetylcysteine can be used as a preventive agent for noise induced hearing loss and to avoid its potentiation with carbon monoxide.

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Background and Aim: Noise-induced hearing loss is the most common problem in industrial areas. This study aimed to determine effects of excessive noise exposure on measurable characteristics of distortion product otoacoustic emissions (DPOAEs) in rabbits.
Methods: The study was carried out on 12 adult male New Zealand White rabbits including case group - exposed to 500-8000 Hz broadband white noise with 100 dBA SPL for 8 hours per day in 5 consecutive days - and control group. After three days period of acclimatization to the experimental condition, rabbits&apos hearing status in each group were measured by distortion product otoacoustic emissions on days zero means before the study was initiated as a baseline, eight, one hour after the latest exposure to noise, and ten. The recorded results were analyzed using SPSS software.
Results: Highest mean distortion product otoacoustic emissions amplitudes in case group were allocated to frequencies of 5888.50 Hz, 8166.50 Hz, 9855.00 Hz, 3956.00 Hz, and 3098.50 Hz, respectively. However, the lowest mean distortion product otoacoustic emissions amplitude was related to frequency of 588.00 Hz (p=0.001).
Conclusion: This study revealed that distortion product otoacoustic emissions amplitude shifts due to noise occur first in high and then in middle frequencies. Additionally, exposure to noise can decrease distortion product otoacoustic emissions amplitudes. We conclude that distortion product otoacoustic emissions can be a reliable test for estimating personal susceptibility to noise-induced hearing loss.

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Background and Aims: Main feature of auditory processing abilities is temporal processing including temporal resolution, temporal ordering, temporal integration and temporal masking. Many studies have shown the superiority of blinds in temporal discrimination over sighted subjects. In this study, temporal processing was compared in congenital blind subjects with sighted controls via gap in noise test (GIN).
Methods: This analytic-prescriptive non-invasive cohort study was conducted on 22 congenital blinds (11 males and 11 females) with a mean age of 26.22 years and 22 sighted control subjects (11 males and 11 females) with a mean age of 24.04 years with normal hearing in faculty of Rehabilitation Tehran University of Medical Sciences. Gap in noise test results, approximate threshold and percent of corrected answers, were obtained and then, were analyzed by Mann-Whitney non-parametric statistical test.
Results: There was a significant difference in the approximate threshold and the percent of corrected answers between congenital blinds and sighted control subjects (p<0.05). However, there was no significant difference between males and females in this regard (p>0.05).
Conclusion: Auditory temporal resolution ability, the lower approximate threshold and the more corrected answers in gap in noise, in blind subjects is better than the sighted control group and it might be related to the compensative neuroplasticity after visual deprivation.

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Background and Aim: Temporal resolution refers to the ability of perceiving changes over time. This study was conducted to prepare Persian version of the temporal resolution test, which was first introduced by Phillips (1994) and Stuart (1996), and to obtain its results in 18 to 25 year old normal individuals of both genders.
Methods: To construct the Persian version of the temporal resolution test, like the original version, speech stimuli, continuous and interrupted noises were used. Speech stimuli comprised four lists of fifty words-monosyllabic lists, which were presented to the right ears first in quietness and then with continuous and interrupted noises on S/Ns of -20, -10, 0, +10 dB. The test was performed on thirty three right handed healthy individuals (14 male and 19 female with the mean age 21.02, SD=1.7 year old) in written response mode.
Results: Significant difference was shown between test scores in quiet with each of the continuous (p<0.0001) and interrupted (p≤0.0001) noises in four signal to noise ratios, and also between test scores of continuous and interrupted noise presentations (p<0.0001). No significant correlation was revealed between gender and test scores and age and test score and age in +10 dB S/N ratio.
Conclusion: Conducting this test on a group of healthy individuals showed its application for measuring temporal resolution with speech stimuli.

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Background and Aim: Sound conditioning is exposure to a non-traumatic, moderate level of sound which increases inner ear resistance against further severe noise. In this study, we aimed to survey the effect of sound conditioning on auditory brainstem response (ABR) threshold shifts using click stimulus, and the effect of the frequency of conditioning on hearing protection.
Methods: Fifteen guinea pigs were randomly divided into 3 groups. Two conditioned groups were exposed to 1 kHz, and 4 kHz octave band noise at 85 dB SPL, 6 hours per day for 5 days, respectively. On the sixth day, the animals were exposed to 4 kHz octave band noise at 105 dB SPL, for 4 hours. The control group was exposed to intense noise, 4 kHz at 105 Db SPL for 4 hours (without conditioning). After exposure, ABR thresholds using click were recorded an hour, and 7 days after noise exposure.
Results: The results of the ABR with click stimulus showed less thresold shifts in conditioned groups than control (p≤0.001). Comparison of the results of conditioned groups, showed less threshold shift by 4 kHz conditioning, however, this difference was not statistically significant (p>0.05).
Conclusion: Electrophysiological data of our study showed that sound conditioning has a protective effect against subsequent intensive noise exposure, and the frequency of conditioning does not have significant effect on ABR threshold shifts when using click stimulus.

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Background and Aim: The temporal processing is one of the critical features in central auditory processing system the gap in noise (GIN) test is the appropriate clinical tool for appraisal of temporal resolution which in people with multiple sclerosis may encounter with complications. Consequently, the aim of this study was to compare the results of gap in noise test in 18 to 40-year-old patients with multiple sclerosis and normal participants.
Methods: This cross-sectional non-invasive cohort study was conducted on 20 patients with relapsing-remitting multiple sclerosis (mean age: 28.9 years) and 26 healthy normal hearing participant (mean age: 27.7 years) in the age range 18 to 40 years. The approximate threshold and percent of corrected responses were obtained and then were analyzed using Student&aposs t-test.
Results: There was an increase in gap detection and decrease in percent of corrected responses in gap in noise test within multiple sclerosis patients in comparison with normal people (p<0.0001). Moreover, there were a correlation of 78% between increasing disease duration and approximate threshold and also a correlation of 82% between increasing disease duration and corrected responses (p<0.0001).
Conclusion: Based on the findings of this study, it seems that people with multiple sclerosis suffer from some degree of disorder in the temporal resolution which might be due to involvement of central nerve system and, somehow, deficit in central auditory processing. Therefore, for evaluating the temporal resolution in people with multiple sclerosis, gap in noise test could be useful.

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Background and Aim: Auditory temporal processing reveals an important aspect of auditory performance, in which a deficit can prevent the child from speaking, language learning and reading. Temporal resolution, which is a subgroup of temporal processing, can be evaluated by gap-in-noise detection test. Regarding the relation of auditory temporal processing deficits and phonologic disorder of children with dyslexia-dysgraphia, the aim of this study was to evaluate these children with the gap-in-noise (GIN) test.
Methods: The gap-in-noise test was performed on 28 normal and 24 dyslexic-dysgraphic children, at the age of 11-12 years old. Mean approximate threshold and percent of corrected answers were compared between the groups.
Results: The mean approximate threshold and percent of corrected answers of the right and left ear had no significant difference between the groups (p>0.05). The mean approximate threshold of children with dyslexia-dysgraphia (6.97 ms, SD=1.09) was significantly (p<0.001) more than that of the normal group (5.05 ms, SD=0.92). The mean related frequency of corrected answers (58.05, SD=4.98%) was less than normal group (69.97, SD=7.16%) (p<0.001).
Conclusion: Abnormal temporal resolution was found in children with dyslexia-dysgraphia based on gap-in-noise test. While the brainstem and auditory cortex are responsible for auditory temporal processing, probably the structural and functional differences of these areas in normal and dyslexic-dysgraphic children lead to abnormal coding of auditory temporal information. As a result, auditory temporal processing is inevitable.

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Background and Aim: Temporal lobe epilepsy (TLE) is one of the most frequent epileptic syndromes in adults. Some patients with epilepsy, especially TLE, have central auditory disorders, such as temporal processing, even though they have normal peripheral auditory function. The Gaps-in-Noise (GIN) test is one of the new tests for assessing auditory temporal resolution. The aim of this study was to evaluate temporal resolution ability in patients with unilateral temporal lobe epilepsy.
Methods: In this cross-sectional and descriptive-analytic study, 25 subjects with temporal lobe epilepsy (11 patients with right temporal lobe epilepsy and 14 patients with left temporal lobe epilepsy) and 18 normal control subjects of 15 to 50 years of age were assessed by the GIN test. Parameters of GIN test were analyzed by one-way ANOVA and compared between the three groups.
Results: There was a significant difference in the mean of approximate threshold and percentage of correct answer in GIN test in the right ear, left ear, and mean of both ears between patients with temporal lobe epilepsy and normal subjects (p<0.05). However, difference between right and left temporal lobe epilepsy groups were not significant (p>0.05).
Conclusion: The lower percentage of correct answer and higher approximate threshold in patients with temporal lobe epilepsy in comparison with the normal control group revealed temporal processing deficiencies especially in temporal resolution abilities. This may be due to involvement of structures related to temporal processing.

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Background and Aim: As word recognition score test is one of the most important tests in audiologic test battery and there is no study on reliability and validity of existing monosyllabic word lists, we decided to investigate this in people with noise induced hearing loss.

Methods: In this non-randomized descriptive-analytic study, 30 adults with noise induced high frequency hearing loss with the age of 18 to 46 years were evaluated. Construct validity was evaluated by comparing Mosleh lists with list NU-6 and reliability was achieved by test-retest (-two-week interval).

Results: The mean (SD) score of word recognition was 94.01 (3.95) percent for list 2, 90.40 (4.90) percent for list 4, 89.08 (4.43) percent for list 5, and 94.10 (4.11) percent for list 9. A reliability of 94% was achieved in all four lists . Regression analysis revealed that word recognition score (WRS) had decreased in proportion to pure tone average.

Conclusion: Four lists have good construct validity. All word lists are phonetically reliable too.

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Background and Aim: Multiple sclerosis (MS) is one of the central nervous system diseases can be associated with a variety of symptoms such as hearing disorders. The main consequence of hearing loss is poor speech perception, and temporal acuity has important role in speech perception. We evaluated the speech perception in silent and in the presence of noise and temporal acuity in patients with multiple sclerosis.

Methods: Eighteen adults with multiple sclerosis with the mean age of 37.28 years and 18 age- and sex- matched controls with the mean age of 38.00 years participated in this study. Temporal acuity and speech perception were evaluated by random gap detection test (GDT) and word recognition score (WRS) in three different signal to noise ratios.

Results: Statistical analysis of test results revealed significant differences between the two groups (p<0.05). Analysis of gap detection test (in 4 sensation levels) and word recognition score in both groups showed significant differences (p<0.001).

Conclusion: According to this survey, the ability of patients with multiple sclerosis to process temporal features of stimulus was impaired. It seems that, this impairment is important factor to decrease word recognition score and speech perception.