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LESSON 60

Finding Air-Conduction Thresholds : Hughson-Westlake

Year 1
Spring semester
Audiological Assessment Methods I
Clinical basics and pure tone audiometry
Duration: 13:08

In pure tone audiometry, air conduction thresholds are found with the modified Hughson-Westlake method. In this lesson, we go step by step through the definition of threshold, familiarization, the down 10 dB, up 5 dB rule, the frequency order, a sample threshold search and common mistakes.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson, we learn how air conduction thresholds are found in pure tone audiometry, using the modified Hughson-Westlake method.
Starting from the definition of threshold, we will follow a sample threshold search step by step and talk about common mistakes.
A threshold is the lowest level at which a person can hear a sound.
But a threshold is not a sharp line; near threshold, the person sometimes hears the sound and sometimes does not.
So the threshold is defined in terms of probability.
In the modified Hughson-Westlake method, threshold is the lowest level at which responses occur on at least half of the ascending trials.
In practice, this means at least two responses on ascending trials at the same level, for example two out of three.
This definition appears in the guidelines of the American Speech-Language-Hearing Association, or ASHA.
The method is named after Hughson and Westlake, who described reaching the threshold with an ascending approach.
Carhart and Jerger simplified this approach and proposed the modified Hughson-Westlake method we use today.
At the heart of the method, the sound is always presented from silence up to an audible level, that is, from below upward.
International guidelines are based on this method, although the descending approach is also widely used in clinical practice.
The method recommended by the British Society of Audiology, or BSA, rests on the same principles.
The threshold can be approached from two directions: presenting the sound from below upward, or from above downward.
In the ascending approach, the sound starts at an inaudible level and is raised step by step.
So the patient responds to a sound they have just detected, and responding out of habit becomes less likely.
The modified Hughson-Westlake method and international guidelines define threshold from these ascending trials.
In the descending approach, the sound starts at a clearly audible level and is lowered until the response stops.
The advantage of this approach is that the patient recognizes the target sound from the start and picks out faint tones more easily.
For this reason, the descending method is more widely used in clinics in Türkiye.
Both approaches have their own advantages; what matters is to apply the chosen method consistently and to state it in the report.
Before starting the test, otoscopy should have been done and the earphones placed correctly.
In air conduction testing, sound is delivered through supra-aural earphones or insert earphones.
The patient presses a button or raises a hand each time they hear the sound.
The patient is seated so that they cannot see the tester's hands or the audiometer display.
This prevents responses prompted by visual cues.
The red earphone goes on the right ear and the blue earphone on the left ear.
The instructions are short and clear: press the button every time you hear a sound, however faint.
Ask the patient to press as soon as they hear the sound and to release when it stops.
Stress that they should respond to every sound they hear, no matter how faint.
After giving the instructions, check with a short question that the patient has understood.
Testing begins with the ear the patient says is the better one.
If the patient reports no difference between the ears, clinics usually start with the right ear.
Testing begins at one thousand hertz, because thresholds are usually measured most consistently at this frequency.
First, a clearly audible tone is given so the patient can learn the sound; the ASHA guideline suggests thirty dB HL for this.
If there is no response, the tone is given at fifty dB HL; if there is still no response, it is raised in ten decibel steps.
When the patient hears the tone and responds, familiarization is complete and the threshold search begins.
The aim of this first response is to help the patient recognize the sound they are listening for.
The rule of the threshold search is simple: when the patient responds, the level is lowered by ten decibels.
When the patient does not respond, the level is raised by five decibels.
This rule is easy to remember as down ten, up five.
Each tone is presented for about one to two seconds.
The silent intervals between tones should be irregular; a rhythmic presentation leads the patient to respond by guessing.
In this method, threshold is determined from the responses on ascending trials.
Now let us follow a sample threshold search at one thousand hertz, step by step.
The patient responds at thirty dB HL; we go down ten decibels to twenty and get a response again.
There is no response at ten dB HL; we go up five decibels to fifteen, and there is still no response.
A response comes at twenty dB HL; this is the first ascending response at twenty.
We go down ten decibels again and up in five decibel steps; there is no response at ten or fifteen.
A response comes again at twenty dB HL; this is the second ascending response at the same level.
Because there was no response at fifteen on either ascending trial, the threshold in this example is recorded as twenty dB HL.
After one thousand hertz, two thousand, four thousand and eight thousand hertz are tested in turn.
Then one thousand hertz is measured again; this retest shows whether the patient's responses are consistent.
The two measurements should usually differ by no more than five decibels; if they do, at least one more frequency is retested.
Then five hundred and two hundred fifty hertz are tested.
The same order is followed in the second ear; according to ASHA, the one thousand hertz retest is not needed in this ear.
In some cases, interoctave frequencies are added to the standard octave frequencies.
If two adjacent octave frequencies differ by twenty decibels or more, the frequency in between is also tested.
Three thousand and six thousand hertz are on the routine list in the ASHA guideline; some clinics test them only by this rule.
Seven hundred fifty and fifteen hundred hertz can also be added in similar situations.
If there is a loss at low frequencies, one hundred twenty five hertz can also be tested.
These extra measurements show the shape of the audiogram more accurately and are also useful in hearing aid fitting.
Audiometers can present the tone in different ways.
Pulsed tones, which switch off and on at short intervals, make the sound easier to detect for many patients.
A continuous tone can also be used; what matters is choosing one presentation mode and using it consistently with each patient.
In sound field testing through loudspeakers, a frequency-modulated tone is used instead of a pure tone.
This prevents standing waves from forming in the room and the sound level from fluctuating at the position of the ear.
Each threshold is marked right away at the line for that frequency.
In this example, the right ear air conduction thresholds are shown with a red circle.
The left ear air conduction thresholds are shown with a blue cross.
In both ears, thresholds are within normal limits up to two thousand hertz; from four thousand hertz there is a mild drop.
Symbols for the same ear are joined with a straight line; we will cover recording standards in a separate lesson.
Marking thresholds as soon as they are found reduces the risk of recording them later at the wrong frequency or for the wrong ear.
If there is no response even at the audiometer's maximum output, that frequency is recorded as no response.
In this case, the symbol is placed at the device limit, with a small downward arrow added below it.
No-response symbols are not joined to neighboring thresholds with a line.
Remember that at very high levels, especially at low frequencies, the patient may feel vibration instead of hearing the sound.
Such a response should not be recorded as a true threshold; it should be noted separately on the audiogram.
If air conduction thresholds are outside normal limits, bone conduction is measured to find the type of loss.
If there is a large difference between the ears, masking may be needed, because the good ear may hear the sound meant for the poor ear.
We will see in detail when and how to mask in the clinical masking lessons.
Speech audiometry results are also compared with pure tone thresholds as a cross-check.
The modified Hughson-Westlake method is designed for people who can understand the instructions and respond with a button.
In young children, the same threshold logic is adapted with play or visual reinforcement methods.
In older patients or those who tire quickly, short breaks improve the consistency of responses.
Whatever method is used, stating the method and the reliability of responses in the report is good practice.
A response given when no sound was presented is called a false positive response.
Rhythmic presentation and the patient guessing while waiting for the next sound increase false positive responses.
Patients with tinnitus, or ringing in the ears, may confuse the tone with their tinnitus; pulsed tones help here.
To catch false positive responses, longer silent intervals are left from time to time to see whether a response comes.
No response when a sound was presented is called a false negative response.
Fatigue, distraction or misunderstood instructions can cause this.
A tip from practice: when responses become inconsistent, stop instead of speeding up.
Give the instructions again briefly and clearly, and go back to the familiarization step if needed.
A one thousand hertz retest that differs by more than five decibels is an early sign that such a step is needed.
Writing a short note on the reliability of responses in the report helps the results to be interpreted correctly.
The threshold can be reached with an ascending or a descending approach; both have their own advantages.
The test begins at one thousand hertz with familiarization using a clearly audible tone.
After a response, go down ten decibels; after no response, go up five decibels.
The frequency order is one thousand hertz, the high frequencies, the one thousand hertz retest and then the low frequencies.
Test yourself: In the modified Hughson-Westlake method, how is the level changed when the patient does not respond?
The correct answer is B: it is raised by five decibels.
The rule in this method is down ten, up five, and the threshold is based on responses on ascending trials.
In the next lesson, we will see how bone conduction thresholds are measured and what the pitfalls of this measurement are.
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Prerequisites

LESSON 59 Preparing for pure-tone audiometry

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