In the current article we will have a look at the evolusion of audiological tests. Based on the Olsen's theory,having  knowledge about the history of audiological evaluation is not a click="function onclick() { this.style.backgroundColor='#b5d5ff'return hotWord(this) }" onmouseout="function onmouseout() { this.style.backgroundColor='transparent' }" onmouseover="function onmouseover() { this.style.cursor='default' }">platitudinous issue, Rather an audiologist should have a comprehensive knowledge about it and be involved in its progress. In this way he can attain enough expertise and science to make use of the technology.The oldest history regarding to this issue goes back to the 16th century,although It should be considered that other  related investigations about sound, hearing and related fields has heretofore been performed and the relevant investgigators should not be ignored.

Background and Aim: Multiple sclerosis (MS) is a neurological disorder that involves central nervous system. Studies have showed that multiple sclerosis affects behavioral central auditory tests, such as masking release or masking level difference (MLD). The purpose of this study is to compare the masking level difference between multiple sclerosis patients and normal subjects.
Methods: This cross sectional and non-interventional study was conducted on 32 multiple sclerosis patients aged between 20-50 years and 32 controls matched for age and gender in Faculty of Rehabilitation, Tehran University of Medical Sciences. masking level difference test was performed on each subject.
Results: The mean masking level difference in the two groups was significantly different (p<0.01) however, gender did not prove to play a role in this difference.
Conclusion: As part of the multiple sclerosis diagnosis panel, masking level difference test is an efficient modality for evaluation of hearing impairment and monitoring of rehabilitation progress.