Pure Tone Audiometry

1. Pure Tone Audiometry • most commonly used test for evaluating auditory sensitivity • delivered primarily through air conduction and bone conduction • displayed on a graphic plot called an audiogram • audiogram represents a patient's ability to hear sounds compared with the hearing sensitivity of a group of normal young adults

2. Pure-Tone Air-Conduction Testing • measure the function of the total hearing system, including the external, middle, and inner ear • Hughson-Westlake "ascending method" - sounds are initially presented well above threshold, decreased to a level of inaudibility in 10- to 15-dB steps, and then increased in "up 5-dB, down 10-dB steps" until the single hearing level at which a response is obtained three times is reached.

3. Because air-conduction thresholds measure the acuity of the entire hearing system, when evaluated alone they provide little information regarding the etiology of hearing loss and specific auditory pathology. • When examined in conjunction with thresholds obtained by bone-conduction testing, however, they help determine both the type and severity of the hearing loss. • 0- to 25-dB – normal • >25 dB - various levels of hearing loss

4. Pure-Tone Bone-Conduction Testing • provide auditory threshold information when the cochlea is stimulated more or less directly, with stimuli bypassing external and middle-ear structures • differences between thresholds obtained through air and bone conduction are used to determine the type of hearing loss (normal hearing vs conductive loss vssensorineural hearing loss [SNHL]) and the magnitude of conductive hearing loss if it exists

5. conductive - when air-conduction thresholds are elevated relative to normal bone-conduction thresholds (air-bone gap) • sensorineural - when air-conduction and bone-conduction thresholds indicate the same amount of hearing loss • mixed - when air-conduction thresholds are elevated relative to abnormal bone-conduction thresholds

6. Speech Testing • evaluation of the listener's ability to detect and recognize speech • determination of the speech detection threshold (SDT), speech reception threshold (SRT), and speech discrimination or recognition

7. SDT - indicative of the intensity level at which a listener can barely discern the presence of a speech signal 50% of the time • listener is not required to recognize the stimulus but is merely asked to acknowledge its presence

8. SRT requires the listener to repeat the word that was presented. • The SRT is usually 8 to 9 dB higher than the SDT,whereas the SDT usually coincides with the pure-tone average (PTA; an average of the pure-tone thresholds obtained at 500, 1000, and 2000 Hz).

9. Speech discrimination provides information regarding the listener's ability to recognize speech under well-controlled conditions. • monosyllabic words presented in an open-set format, such as the CID W-22 word lists and NU-6 • Taped materials are optimal but materials are often presented through live voice for rapidity and ease of administration • Speech discrimination materials are usually presented 50 dB above the patient's SRT which should be well within their audible range.

10. Masking • When conducting either pure-tone or speech testing, a masking signal to the ear that is not being tested may be needed. If a sufficiently loud signal is presented to the test ear, it may cross the skull where it will be perceived by the non-test ear, a phenomenon referred to as crossover.

11. When this occurs, responses to air-conducted pure tones that have crossed over from the poorer ear will actually shadow the thresholds of the better ear. Such "shadow" responses reflect the threshold levels of the better ear, elevated by the amount of interaural attenuation at each test frequency. • interaural attenuation - reduction in sound when it crosses from one ear to the other