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: 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.