The Naval Aviator S Speech Discrimination Test

The Naval Aviator's Speech Discrimination Test (NASDT), formulated in 1964, is used by the Bureau of Medicine and Surgery to evaluate aviators who fail to meet the hearing standards for aviation. The nature of the test, which involves a listening task for high-level speech signals with a simulated aircraft noise background, requires a tape recorder and earphone configuration. Two similar systems of test presentation have been developed and are in current use at 18 Navy and Marine Corps installations. The devices produce the properly controlled test signals required for the NASDT and are easily operated by trained corpsmen. Additional information is presented to enable the user of either system to administer the test properly.

The pure tone threshold audiogram required annually for naval aviators provides limited information toward determining their ability to understand speech in the aircraft. The Naval Aviator's Speech Discrimination Test (NASDT) was developed to evaluate objectively the ability to understand very loud speech in a background of aircraft noise for those aviators whose hearing failed to meet the standards. An earlier study had indicated that there was no relationship between the results of the NASDT and the configuration of the pure tone audiogram; therefore, to further examine this finding, data from pure tone threshold tests and the NASDT were obtained for over 500 men with different degrees of flight experience. Statistical analysis of the NASDT results showed that there was great consistency in scores made by the different groups. No practical correlations between NASDT scores and hearing threshold levels were found. Since the NASDT, therefore, appears to provide a more realistic evaluation of hearing in aircraft noise, it is suggested that it be employed as a supplementary test in the hearing evaluations of all aviators.

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