The Hughson-Westlake method specifies how you to obtain threshold. The key points are:
- When the patient hears the tone, decrease the intensity 10 dB
- When the patient does not hear the tone, increase the intensity 5 dB
- You are seeking the lowest intensity at which the patient hears the tone at least 50% of the time.
Start by presenting an air-conduction tone in the better ear. We generally want to start testing by presenting a tone that the patient can easily hear. If the patient is normal hearing, a 1000 Hz tone at 30 dB HL is a reasonable starting point.
In the “initial descent”, you are reducing the tone intensity to a level that is below threshold. You do not use these presentations when you are calculating whether the patient heard the tone. You begin your “counting” the first time the patient does not hear the tone (but only after the patient has provided you with one or more responses at that frequency).
Assume the actual patient threshold is 5 dB HL.
- You present the tone at 30 dB HL and the patient hears it and pushes the response button
- You decrease the intensity 10 dB, to 20 dB HL, and present the tone. The patient responds.
- You decrease the intensity to 10 dB HL, and the patient responds.
- You decrease the intensity to 0 dB HL, and the patient does not respond.
You have now completed the “initial descent” and start counting with the no response at 0 dB HL
After you have made the "initial descent”, you increase the intensity in 5 dB steps whenever the patient does not hear the tone, and decrease it by 10 dB whenever the tone is heard. You have found threshold when you find the lowest level at which the person responds in at least 50% of three trials, and have verified that the patient does not respond to at least 50% of three trials at a level that is 5 dB lower.
Again, assume the actual patient threshold is 5 dB HL.
- The tone was not heard at 0 dB HL during the initial descent.
- You turn the tone up to 5 dB HL and present the tone. It is heard. (That’s 1 response / 1 presentation)
- Decrease the tone 10 dB to –5 dB HL, and present the tone. It is not heard. (0 / 1)
- Increase the tone 5 dB to 0 dB HL, and present the tone. It is not heard (0 / 2)
- Increase the tone 5 dB to 5 dB HL, and present the tone. It is heard. (That’s 2 / 2)
Since the patient has 2 / 2 responses at 5 dB HL and 0 / 2 responses at 0 dB HL, you have obtained threshold = 5 dB HL.
If at one level, the patient hears the tone 2 / 2 times, and at the level 5 dB lower, the tone was not heard in either of 2 tries (0 / 2 responses), then that is threshold. Regardless of what happens on the third try, threshold would not change.
- There was no response at 0 dB HL after initial descent.
- 5 dB HL – no response
- 10 dB HL – response
- 0 dB HL – no response
- 5 dB HL – response (there has now been a response in 1 of 2 presentations)
- -5 dB HL – no response
- 0 dB HL– response
- 5 dB HL – response (there have been 2 / 3 responses, this is threshold).
At the level 0 dB HL, there were 0 / 3 responses. You know this is not threshold.)
- 1000 Hz
- 2000 Hz
- 3000 Hz
- 4000 Hz
- 8000 Hz
- 1000 Hz (Re-Test)
- 500 Hz
- 250 Hz
Mid-octave frequencies are tested if needed. The better ear is tested first, then the poorer ear is tested.
Doubling the frequency is an octave increase (e.g. from 1000 to 2000 Hz). When there has been a 20 dB or more difference in the thresholds at adjacent octaves, then the midoctave frequency should be tested. The midoctave frequency in this case is 1500 Hz. On the audiogram, the octave frequencies are shown with solid lines, the midoctave frequencies are usually shown with thinner or dotted lines.
When doing (unmasked) bone conduction testing, start with the better ear, if one is significantly better. Starting with the better ear makes masking easier.
For the audiometer simulator programs, you should test both ears by bone conduction unless your instructor has told you otherwise.
Threshold testing methods are the same in air- and bone-conduction testing. However, you cannot test 125 Hz, nor 8000 Hz. 6000 Hz is generally not tested.
The audiometer is not able to produce bone-conduction signals at as loud a maximum intensity as is feasible during air-conduction testing. If your patient has a severe or profound loss, you may find that you are marking “no response” fairly often.