8 HEARING MEASUREMENT John R. Franks, Ph.D. Chief, Hearing Loss Prevention Section Engineering and Physical Hazards Branch Division of Applied Research and Technology National Institute for Occupational Safety and Health Robert A. Taft Laboratories 4676 Columbia Parkway Cincinnati, Ohio 45226-1998 USA
[email protected] 8.1. INTRODUCTION (RATIONALE FOR AUDIOMETRY) The audiogram is a picture of how a person hears at a given place and time under given conditions. The audiogram may be used to describe the hearing of a person for the various frequencies tested. It may be used to calculate the amount of hearing handicap a person has. And, it may be used as a tool to determine the cause of a person’s hearing loss. Audiograms may be obtained in many ways; e.g., by using pure tones via air conduction or bone conduction for behavioral testing or by using tone pips to generate auditory brainstem responses. The audiogram is a most unusual biometric test. It is often incorrectly compared to a vision test. In the audiogram, the goal is to determine the lowest signal level a person can hear. In the case of a vision test, the person reads the smallest size of print that he or she can see, the auditory equivalent of identifying the least perceptible difference between two sounds. In most occupational and medical settings, this requires the listener to respond to very low levels of sounds that he or she does not hear in normal day-to-day life. A vision test analogous to an audiogram would require a person to sit in a totally darkened room and be tested for the lowest luminosity light of various colors, red to blue, that can be seen.