What does an audiogram show?
The audiogram is a plot of a person’s hearing thresholds. Across the top of the audiogram is the pitch of the tones, from low to high pitch, plotted in frequency from 250 to 8000 Hertz (Hz). The level in decibels (dB) is plotted down the side. The normal range of hearing is from 0 to 20 decibels hearing level (dBHL).
- Air conduction hearing thresholds:
When a child is tested with sound presented through earphones, air conduction hearing thresholds are measured, representing hearing sensitivity for the entire hearing system. Because sound is presented to each individual ear, information can be gathered about the hearing in each ear, separately. The symbols used to represent air conduction testing are an X for the left ear and an O for the right ear. Sometimes colors are used for all of the different symbols: red for the right and blue for the left. If the child was tested with sounds presented from a loudspeaker, also called sound field, the hearing thresholds will be plotted with an S. Sound field hearing thresholds will reflect the hearing of the better ear, if there is a difference between ears. Ideally, children are tested under earphones to obtain information about each ear individually. However, in infants and toddlers, earphones, even small insert earphones, are often rejected by the child and testing can only be conducted from the loudspeaker. If the child does not hear the sound at the loudest level of the audiometer (the machine used to test hearing), it may be indicated several different ways, with a NR (no response), or an arrow downward from the X or O.
- Bone conduction hearing thresholds:
Auditory stimuli can also be bone conduction, a small box that sits behind the ear on the mastoid bone and presents sound by vibration to the inner ear. Bone conduction thresholds are represented by the symbols > and < on the audiogram. Bone conduction represent the responses from the inner ear, as the bone conducted signal bypasses the outer and middle ear systems. A comparison of bone and air conduction thresholds allows the audiologist to determine the type of hearing loss (conductive, sensorineural, or mixed).
This audiogram shows air conduction thresholds for a person with a moderate hearing loss:
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