ANNABELLA BLUESKY / SCIENCE PHOTO LIBRARY ANNABELLA BLUESKY / SCIENCE PHOTO LIBRARY
Pure-tone audiometry test. Teenage girl having the sensitivity of hearing tested with an audiometer. Pure-tone sounds of different frequencies are generated electronically by the audiometer machine (bottom right) and are played through the headphones to the girl's ears. She uses the button in her right hand to 'click' along with the tones when she can hear them. In this way the pure-tone threshold (PTT) or auditory threshold is determined for each frequency. The PTT is the minimum intensity of sound required for that frequency to be audible. This also produces an audiogram, an important chart of the extent of hearing loss at different frequencies.
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