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Accurate assessment of hearing (Audiometry) is vital to the diagnostic evaluation of patients with suspected autologic disorders for the determination of the underlying process, as well as in the planning of rehabilitation of hearing loss. Originally, audiometry was limited to the psychophysical measurement of the sensation of hearing. Thus, patient cooperation was essential. However, other tests have been developed over the years which permit more objective assessment of hearing even in infants, small children, malingerers, and hysterics.

Human hearing
Most humans hear sounds in the range of 20 to 20,000 Hz. Sensitivity varies as a function of frequency, with sounds in the middle frequencies being heard best. The ability to hear higher frequencies declines with age. For a discussion of the causes of hearing loss, see the section on diseases of the middle ear, or diseases of the inner ear.

Basic audiometry
Adequate testing requires an audiometer (device for presenting sounds to the patient at a precisely controlled intensity), a sound-proof environment, a competent audiologist, and a cooperative patient. The standard testing battery includes pure tone audiometry, speech audiometry, and immittance audiometry.

Pure tone audiogram
This is a graphic plot of the patient’s thresholds of auditory sensitivity for pure tone (sine wave) stimuli. Threshold hearing levels are indicated for each frequency tested. By convention, normal hearing levels are shown at top of the graph, a decrease in hearing sensitivity is indicated by larger values of hearing level. Hearing level is plotted on a logarithmic decibel scale. Sounds are tested with presentation by air conduction (earphones) as well as bone conduction (skull vibrator). An air bone gap indicates a conductive component of hearing loss. A decrease in threshold sensitivity by bone conduction reflects a sensory or neural loss.

Air conduction thresholds are represented by circles, and bone conduction by triangles. A solid symbol indicates that masking noise was presented to the opposite ear to minimize the chance of responses due to crossover of sound.

This sample audiogram indicates normal hearing in the right ear, and a conductive loss on the left.

Right Ear Left Ear
Normal hearing Conductive hearing loss

The second audiogram demonstrates a sensory–neural loss in the right ear, and a mixed loss on the left.

Right Ear Left Ear
Sensory–neural hearing loss Mixed hearing loss
Adequate testing requires

Speech audiometry
These tests utilize spoken words and sentences rather than pure tones. Tests are designed to assess sensitivity (threshold) or understanding (intelligibility). Immittance audiometry
These hearing tests utilize the electro–acoustic immittance bridge. This device is designed to quantify the impendence (resistance to movement) of the conductive mechanism of the ear by bouncing a probe tone off the tympanic membrane and measuring the proportion of reflected sound.