OAEs are sound founds in the external aditory meatus that originate in the cochlea. OAEs are generated only when the organ of corti is in near normal condition and They can be detected only when the middle ear system is operating normally. The sound generated by the cochlea are small but  potentially audible, sometimes as much as 30 dBSPL. They can emerge spontaneously in the cochlea, but more commonly OAEs follow acoustic stimulation. No electrod are needed to  observe OAEs. In fact, microphone are used to detect them.

Objective: determining difference limen for Frequency (DLF)in string musicians.
Materials &Methods: This case-control study was conducted on 15 string musicians with musicianship > 10 years (30 ears) and 15 normal hearing subjects (30 ears). They all were male and 20-30 years old. DLF was measured after otoscopy and immitance audiometry and pure tone audiometry.
Results: DLF was significantly different between two groups of case and control. DLF in musicians is less than the normal hearing subjects.
Conclusion: It seems that familiarization with notes results in better DLF in musicians comparing to others.

Background and Aim: Middle latency auditory evoked potentials (MLAEPs) development takes longer time than the auditory brainstem response (ABR) development does, which makes them difficult to record in some children. The purpose of this study was to investigate the age effect on characteristics and detection of MLAEPs in children and adults.
Materials and Methods: This cross sectional study was conducted on 15 children aged   7-12 yr and 31 adults aged 20-50 yr with normal peripheral hearing. To investigate precisely, children were divided in two subgroups of older and younger than 10 years old, as well. The MLAEPs amplitudes and latencies were recorded by conventional protocol and compared.
Results: Adult Na mean latency, 20.86 ms, was less than that of children, 22.86 ms, (p=0.0025).  In contrast, the adult Nb mean latency, 44.93 ms, was longer (p=0.0001). Children Nb mean latency was 42.02 ms. There was no significant difference in MLAEP amplitudes and latencies between two children subgroups, although variance was more in younger children.
Conclusion: MLAEPs are reliably recorded after 7 years old. Characteristics of MLAEPs are different in adults and children so that the primary MLAEPs generators have a course of development extending beyond the first decade of life. As those potentials were recorded in all children, it is suggested to be used in their test batteries for hearing evaluation.

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.

Background and Aim: Following an early visual deprivation, the neural network involved in processing auditory spatial information undergoes a profound reorganization. In order to investigate this process, event-related potentials provide accurate information about time course neural activation as well as perception and cognitive processes. In this study, the latency and amplitude of auditory P300 were compared in sighted and early blind individuals in age range of 18-25 years old.

Methods: In this cross-sectional study, auditory P300 potential was measured in conventional oddball paradigm by using two tone burst stimuli (1000 and 2000 Hz) on 40 sighted subjects and 19 early blind subjects with mean age 20.94 years old.

Results: The mean latency of P300 in early blind subjects was significantly smaller than sighted subjects (p=0.00.( There was no significant difference in amplitude between two groups (p>0.05).

Conclusion: Reduced latency of P300 in early blind subjects in comparison to sighted subjects probably indicates the rate of automatic processing and information categorization is faster in early blind subjects because of sensory compensation. It seems that neural plasticity increases the rate of auditory processing and attention in early blind subjects.

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.

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.

Bachground and Aim: The involvement of central auditory nervous system is relatively prevalent in patients suffering from multiple sclerosis (MS). To understand cortex function and to investigate cognitive impairment, event related potential is considered as a valuable tool. This study was aimed to compare the amplitude and latency of the event related potentials of P300 in MS patients and normal individuals.
Methods: This cross sectional study was conducted on 21 MS patients and 27 normal cases aged 18-50 years. Auditory P300 was recorded with oddball paradigm, using two tone burst stimuli (1000 and 2000).
Results: In MS patients, mean latencies were significantly longer (p<0.001) and mean amplitude were significantly lower (p<0.001), in both males and females. Sex did not affect P300 latencies and amplitudes significantly.
Conclusion: MS patients show some degree of event related potential abnormalities. Combination of auditory P300 and neuropsychological tests may be useful to investigate cognitive impairment in MS patients.

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.

Background and Aim: Multiple sclerosis (MS) is characterized with inflammation, demyelization and gliosis. It may be relapsing, remitting, or progressive. Cognitive impairment is relatively prevalent in patients wit h multiple sclerosis and as duration of disease is longer as cognition impairment is more. To understand the cognitive impairment, event related potential can be considered as a valuable tool. This study aimed to investigate the influence of duration of disease and expanded disability status scale (EDSS) on the amplitude and latency of the event related potentials of P300 in patients with multiple sclerosis.

Methods: In this cross-sectional and non-intervention study, 21 patients with multiple sclerosis with mean age of 27.8 with SD 7.1 years (between 18 to 50 years) were enrolled. The patients were selected randomly. The correlation of P300 event-related potential and oddball paradigm was assessed, using two 1000 and 2000 Hz tone burst stimulus.

Results: There was a significant correlation between the latency of P300 wave and duration of disease and expanded disability status scale (p < 0.05) there was high correlation in both electrode sites (r>0.50). The correlation of amplitude of P300 and duration of disease and expanded disability status scale was not significant (p>0.05).

Conclusion: Significant correlation between the latency of P300 and the duration of multiple sclerosis and expanded disability status scale can be a sign of central nervous system changes. Besides, there is a relation between physical disability and cognitive impairments.