Masking is a necessary part in ABR test the same as other Audiological experiments to obtain the real responses without the intrusion of the other ear. In the current research we are aimed at studying the effect of the masking noise on the pure latency of wave V and interwave latencies of I-III, III-V and I-V. Noise was delivered to the non test ear with intensities of 0, 30, 50 and 70 dB in four different sessions while the intensity level of the stimulus was fixed in all four sessions.

Rehabilitation of deaf individual is one of the important subjects that has attracted attention of many researchers during past centuries. Different opinions have been established in this direction. Electrophysiologic tests were established and developed parallel to developments in rehabilitation. Therefore, opinion of using electrophysiologic test for evaluation and fitting of hearing aid became gradually popular. Ultimately, the electrophysiologic tests are used in evaluation and fitting of hearing aid in two ways:1-Direct way2- Indirect wayIn direct way aided ABR is obtained and special attention is paid to wave V. This technique has many difficulties. Inindirect way, electrophysiologic tests such, ECochG, OAE and ABR, AMLR, ALR and P300 and other objective tests are used, especially in infants and neonates for evaluating the state of hearing. Researches are continuing in this field. It is probable to have aided electrophysiologic responses with speech stimuli in near future.

Method & Material: This study was performed on 36 normal-hearing subjects aged 18-25 years for survey of temporary threshold shift (TTS) by transient evoked otoacoustic emissions. Finding: Noise can affect the pure-tone thresholds and (TEOAEs) amplitudes. When cochlea affected by noise, evaluating TEOAE is more suitable than pure-tone audiometry. Because of this test, is objective an unaffected by attention and alertness and can be evaluated in difficult to test subject and also have high carefulness and can be performed in a quiet, but not sound-proof room.

Objective: The purpose of study was identify hearing loss in thalassemic patients with history of Desferrioxamine (DFO) therapy. This study was carried out in a cross-sectional descriptive survey on 195 thalassemic patients (3-30 years old) in Gazvin Thalassemia center and Tehran pediatrics&apos medical center.
Methods: The patients underwent routine otolaryngologic history and physical examination, along with standard pure-tone audiometry.
Results: Hearing loss was present in 43.1% of patients. 16% of patients had conductive hearing loss and 4.6% of patient had sensory neural hearing loss. 22.5% of thalassemic patients had high-frequency sensory neural hearing loss and more importantly, high-frequency hearing loss attributable to Desferrioxamine ototoxicity was present in 12% of patients. Furthermore, these evaluations showed that there is a significant relationship between hearing loss and DFO usage and hearing loss too. There is no significant relationship between hearing loss and ferritin level between hearing loss and age of DFO usage too.
Conclusion: Management of these patients requires proper dosing of Desferrioxamine, along with regular otolaryngolgic and audiometric follow-up in order to prevent the effect of ototoxicity of desferal.

Objective: A survey on hearing state of blind schoolboys in Tehran.
Method and Material: This cross-sectional descriptive survey was conducted on 640 ears of 320 blind schoolboys of 5-23 years old as a hearing screening in Tehran blind schools, 2000-01.
Results: 20.94% was hearing-impaired of whom 13.75% had bilateral and 7.19% had unilateral hearing loss. 15.16% of students suffered from sensory-neural hearing loss (SNHL), 1.56% from conductive hearing loss (CHL) and 0.62% from mixed hearing loss (MHL), that is, SNHL occurred 10 times more than CHL. Hearing loss was often mild and moderate, and audiogram configuration was primarily high tone loss (HTL). On the whole, 8.13% of students needed medical treatment, 15.13% needed audiological rehabilitation and 3.44% of them were in need of both medical and rehabilitation Intervention. General information about hearing problem was very low among students, their parents and teachers, which was 26.87%, 20.9% and 22.39%, respectively. There is significant relation between SNHL and parents&apos relationship.
Conclusion: The prevalence of hearing loss in blinds is higher than in normal-visions. It is often sensorineural. So, it is important to identify these children through hearing screening (Using more high frequencies) and to conduct medical as well as rehabilitative intervention.

Objective: As the cerebrovascular diseases (CVD) are among the most common anomalies that are directly or indirectly affecting the auditory cortex, studying in this area is important. We tried to evaluate the function of CANS in a group of 50-70 years old cerebrovascular accident (CVA) patients with no hearing complaint by competing sentences test (CST) as a dichotic speech test.
Method and Material: This cross-sectional analytical study was conducted at Loghman-e-Hakim hospital between 22, august 1999 and 20, July 2000 in a group of 30 normal 50-70 years old persons and a group of 40 patients with CVA including 30 patients with abnormal CT scan and 10 patients with normal CT scan.
Results: The results point out the mean scores of CST in the normal group were at normal range (80-100%) in both ears. And mean scores of CST decreased in the patients groups. There were significant difference between mean scores of CST in the patients with CVA and control groups. Conclusion: CST seems to be a valuable test in the CANS test batteries for the cerebrovascular diseases.

Objective:Determining the prevalence of hearing loss and correlated factors in clients referring to audiology clinic of Buali hospital.
Method and Material: This cross-sectional analytic-descriptive survery was carried out on six thousand and twenty ears of 3010 clients (1651 ,ae amd 1359 female) in Audiology clinic of Buali hospital , during Sept 2000 to Sept 2001.
Results: Hearing loss is the most common reason for referring the clients (20.5%). 1319 ears (21.9%) Showed sensorineural hearing impairment and conductive and mixed hearing loss are observed in 1059 (17.6%) and 234 (3.9%) ears, respectedly. Hearing loss degree most cases is mild (14%) in both ears. There is no significant difference between male and female hearing threshold means (p>0.05) ‘ but a significant difference between hearing thresholds is observed in terms of age (p<0.05). Audiogram configuration in most cases is flat (55.1%). Otoscopic examination reveals abnormal condition in 2333 ears (38.8%) . 37.2% of the studied cases have abnormal tympanogram mostly type B (15.9%). 2.2% of the clients wear hearing aid that mostly have B.T.E ones (1.5%). 6.2% of the clients , depends on their hearing impairment type and degree need rehabilitation services.
Conclusion: The results are Valid only in the context of this study and it&aposs generaliztion needs further researches.

Objective: To determine phonological processing in elemantery children with Down syndrome

Materials and Methods: Phonetic test is used to extract phonological processing in 40 child with Down syndrome .They were normal in hearing and oral structure.
Results: There was significant difference between girls and boys in some subgroups of phonological processing. In assimilation, voiceless assimilation in boys and complete assimilation in girls were the most. Nasal assimilation in girls and fricative assimilation in boys were the least. In substitution, the least mean belonged to liquid and nasal substitution in girls and voice ness substitution in boys. In general there was no significant difference between age and phonological awareness however, there was direct correlation between syllable structure and age and reverse correlation between age and stop assimilation.
Conclusion: In addition to 3 groups of phonological processing including: syllable structure, assimilation, and substitution, omission was seen. The difference between girls and boys indicates they are impressed by the phonetic structure of words in different ways. Correlation between age and phonological processing shows phonological errors may be resulted from deviation.

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.

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.

Background and Aim: Previous studies suggest that auditory stimulus frequency in normal subjects contribute to both P300 amplitude and latency measures. As occipital cortex devotes to other modalities including auditory inputs, the purpose of this study was to determine the effects of stimulus frequency in early blind subjects.
Methods: fifteen early blind subjects (8 males and 7 females) with mean age of 25.13±4.27 years were tested. Cognitive potential P300 was recorded in response to high (1000/2000 Hz ) and low (250/500 Hz) frequencies auditory stimuli using an oddball task in 70 dB nHL. While participants answered to target stimulus, amplitude and latency of P300 was recorded.
Results: With high frequency stimuli, mean amplitude in early onset blind subjects obtained 14.13 ±5.53µv and was 17.59±8.17µv with low frequency. With high and low frequency, mean latency of P300 obtained 295.60±31.33ms and 317.38±21.71ms respectively.
Comparison of results between two stimuli showed that there were statistically significant differences between amplitudes (p=0.008) and latencies (p=0.001) of cognitive potential P300.
Conclusion: Changing low frequency to high frequency results in decreasing both amplitude and latency. It seems that auditory stimuli frequency affect the P300 parameters in blind subjects.

Background and Aim: Vestibular-Evoked Myogenic Potentials (VEMP) is a new vestibular function test that assesses the vestibulospinal pathway.
Although many studies have investigated different inner ear pathologies by using VEMP, the role of this test in brainstem pathologies and demyelinating processes of central nervous system is still remained to be defined and discussed.
The aim of this study was to compare VEMP in multiple sclerosis patients and normal individuals.
Methods: We carried out a cross-sectional study in 21 patients (15 female, 6 male) fulfilling diagnostic criteria of clinically definite multiple sclerosis, and 20 normal individuals (15 female, 6 male). ages ranging from 17 to 50 years old.
The VEMPs was recorded using 500 Hz short tone burst (STB). The p13 and n23 latencies and p13-n23 peak-to-peak amplitude were the studied parameters.
Results: VEMP results were abnormal in 47.6% of patients. P13 latency and p13-n23 peak to peak amplitude in both ears showed significant difference between the two groups (p<0.05). P13 latency was delayed in 14 ears (of nine patients). VEMPs were unilaterally absent in two patients.
Conclusion: VEMPs thus represent a new method of the brainstem in multiple sclerosis disease. VEMP abnormalities in these patients might be due to impairment in vestibulocollic pathway.