Pure Tone Audiology Assessment
As part of your hearing evaluation you will undergo what is called pure tone audiometry. Pure tone audiometry is usually completed while you are seated in a sound isolated booth. During this test an audiometer is used to generate auditory signals of different pitches (frequencies) or "pure tones". Testing is completed across the frequency range used for hearing conversational speech. During pure tone testing you will be asked to respond each time you hear the tone. Adult patients usually push a button when the tone is heard and children frequently raise their hand. The responses are called thresholds and represent the level at which tones are barely audible.
The test signal can be presented through earphones, or through a small vibrator, which delivers the tones through the vibration of the skull, or through loud speakers. Signals presented through the earphones are used to determine your hearing sensitivity in each ear. Signals presented through the bone vibrator are used to determine how well you could hear if your ears were functioning normally, your actual "hearing potential". For young children who will not wear earphones, the test signal is presented via a speaker.
Thresholds, the softest sound you can hear, are recorded on an audiogram. On the audiogram shown on the left, it can be seen that pitches (how high or low a tone is) are indicated across the horizontal axis of the audiogram, and hearing sensitivity is indicated on the vertical axis. On this audiogram, you can see the loudness and frequency range of the different speech sounds. Pitches below 1000Hz are considered the lower frequencies and you will notice that vowels and several consonant sounds are in the low frequency area of the audiogram (for example m and e). Frequencies above 1000Hz are considered the higher frequencies, and there are several high frequency consonants in that area (for example k and f). By plotting a patient’s hearing thresholds on this audiogram it would be easy to see which speech sounds can and cannot be heard. As long as hearing thresholds are well above the speech sounds on the audiogram and are above whispered speech (picture of two monkeys whispering), hearing is considered within normal limits because there is no hearing handicap which would interfere with communication.
The different loudness levels of environmental sounds can also be seen on this audiogram. The softer sounds are towards the top of the audiogram (whispered speech at 20dB) and as you look farther down the audiogram, louder sounds are pictured (baby crying at 60dB). Pictured at the bottom of the audiogram are very loud sounds. Loud sounds pictured in the low frequency area are a lawn mower and an eighteen-wheeler truck. Loud sounds pictured in the mid frequency area are a chain saw and a rock band. Loud sounds pictured in the high frequency area are a helicopter and a jet plane.
Completing pure tone audiometry is an important part of audiological assessment. Most subsequent tests done during audiological assessment are administered at loudness levels based on the pure tone results.