A guide to conducting speech audiometry testing

Overview of this guideWelcome to this guide on conducting speech audiometry testing. It will help you to:

• understand the purpose of speech audiometry

• clarify what client information you need

• outline the equipment you need

• conduct the test

• record and interpret the results, and

• determine if your client needs a referral to either a general practitioner or ear, nose and throat specialist.

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Speech audiometrySpeech audiometry is an important part of audiological assessment. We use it to evaluate:

speech perception threshold

speech reception threshold, or SRT

speech discrimination ability, and

to check the validity of pure tone audiogram test results.

With this information the clinician can build up a picture of the client’s needs to determine appropriate hearing aids.

Information needed before conducting the testThere are some key pieces of information you will need before conducting speech audiometry testing.

Ultimately, you are trying to work out if speech masking is required and if so to what level.

Our ears can compensate for each other especially if the hearing in one ear is better than the other. An audiometer can generate noise in the non-test ear to mask or remove it from the test. This prevents the good ear from affecting the accuracy of the results.

To determine speech masking follow these steps:

Step 1 - Obtain a pure tone audiogram for the client.

Step 2 - From the audiogram calculate the three frequency average hearing level, or 3FAHL. This is calculated from the hearing threshold level, or HTL, at frequencies of 500Hz, 1000Hz and 2000Hz.

Step 3 - The three frequency average is then used to calculate the presentation level, or PL, for each ear.

Step 4 - Find the minimum discrimination score level, or MDSL, for the test audiometer.

Step 5 - Use the three frequency average hearing level, the presentation level, the minimum discrimination score level and the interaural attenuation, or IA, to calculate the cross-heard signal. The cross-heard signal tells you if the good ear is helping the bad ear.

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Step 6 - Find the effective speech masking level, or ESML, for the test audiometer.

Step 7 - Calculate the level of masking required.

Understanding the audiogramPure tone audiograms contain several key features you need to understand to be able to perform speech masking calculations.

the results for the right ear are shown as circles

the results for the left ear are shown as crosses

the horizontal or x-axis indicates frequency in hertz (Hz)

the vertical or y-axis indicates the hearing threshold level in decibels (dB)

additional symbols are used to show left and right ear bone conduction.

Calculating the 3FAHL and PLTo calculate the three frequency average hearing level and the presentation level follow these steps:

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Do the calculation for one ear at a time. Typically you start with the ear showing the most hearing loss. In this example the left ear.

Read from the pure tone audiogram the hearing threshold levels, for 500Hz, 1000Hz and 2000Hz. These three frequencies are always included in the test. Using the example audiogram start with the left ear which has the lower level of hearing. Find 500Hz, drop down to the hearing threshold, then look across at the value in decibels. In this case it is 30dB. At 1000Hz the hearing threshold is 40dB. At 2000Hz the hearing threshold is 50dB.

Add all three hearing threshold levels together. The result in the example is 120dB. Now divide by three to get the average. The example three frequency average hearing level for the left ear is 40dB.

To calculate the presentation level add 30dB. 30dB is a standard used to bring the presentation level up to a comfortable starting point. In this example add 30dB and the resulting presentation level for the left ear is 70dB.

Repeat these calculations for the other ear. In this example the right ear shows 10dB for all three frequencies, so the average is 10dB. Add 30dB to get a presentation level for the right ear of 40dB.

Calculate the cross-heard signalThe cross-heard signal is a measurement to determine if any of the test sounds will cross-over and be heard by the non-test ear.

To calculate the cross-heard signal you need the following:

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The three frequency average hearing level and presentation level for each ear.

The interaural attenuation, or IA. This indicates the loss in energy as sound passes from one side of the head to the other. For supra-aural earphones the interaural attenuation is 40dB. For insert earphones the interaural attenuation is 60dB.

The minimum discrimination score level, or MDSL. The MDSL is pre-determined for each audiometer. If there is no value available use -5.

The formula is - cross-heard signal equals presentation level of the test ear, minus the interaural attenuation, minus the three frequency average hearing level (bone conduction) in the non-test ear, minus the minimum discrimination score level.

In the example, the cross-heard signal equals the presentation level of the left ear which is 70dB, minus 40dB interaural attenuation for supra-aural headphones, minus the three frequency average hearing level for the right ear which is 10dB, minus minus 5 or plus 5 for the minimum discrimination score level.

The resulting cross-heard signal is 25dB.

Does this level of cross-heard signal require masking? This is determined by asking if the cross-heard signal is greater than or equal to the three frequency average hearing level (bone conduction) of the non-test ear. In other words will the non-test ear help the test ear?

In the example, the 25dB cross-heard signal is greater than the 10dB three frequency average hearing level in the non-test ear. Therefore masking will be required.

How much masking is required?To calculate the level of masking required you will need the following:

The three frequency average hearing level, air conduction, for the non test ear.

The cross-heard signal, and

The effective speech masking level for the audiometer you will be using. The ESML is pre-determined for each audiometer. If there is no value available and the audiometer uses speech-weighted noise, use a value of 10.

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The formula is…masking level equals, the three frequency average hearing level (air conduction) for the non-test ear, plus the cross-heard signal, plus the effective speech masking level.

In the example, when testing the left ear, the masking level equals the three frequency average hearing level (air conduction) for the right ear which is 10dB, plus 25dB for the cross-heard signal, plus 10dB for the effective speech masking level.

The resulting masking level for the right ear is 45dB.

You now have all of the information required to conduct the speech audiometry test.

What equipment will you need?To conduct speech audiometry testing you need the following equipment:

An audiometer.

A pair of earphones - the example image shows a pair of supra-aural earphones but you might also use insert earphones, and

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Recordings of word lists. You may also provide the words to the client through the audiometer microphone but you must ensure that the client does not ‘lip read’ as you say the words.

Conducting the speech audiometry testHere is an overview of the steps you need to take when performing speech audiometry testing:

Step 1 - Make sure the client is seated comfortably before starting.

Step 2 - Give the client an overview of how the test will be carried out and give them an opportunity to ask any questions.

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Step 3 - Place the earphones on the client and set the audiometer to the presentation level for the test ear. Test one ear at a time and start with the good ear.

Step 4 - Instruct the client through the headphones for any further instructions.

Step 5 - Test the first word list. Use AB (Arthur Boothroyd) word lists which consist of ten words per list and each word has three phonemes or speech sounds. Also be aware that the words you use must be culturally and age appropriate.

Step 6 - Record the client’s response as they repeat each word. If the client gets all three phonemes correct, give a score of 10. Two phonemes correct, a score of 7. One phoneme correct, a score of 3. If they cannot repeat the word, a score of 0. Adding together all the scores in the ten word list will give you a total score as a percentage.

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Step 7 - Determine the client’s speech reception threshold, or SRT. This is done by incrementally decreasing the presentation level until the score is close to 50%. Each decrease should be of 10dB and a new word list should be used.

Step 8 - Determine the client’s PB maximum score, or PBmax. This is done by returning to the starting presentation level and incrementally increasing the level until the score is 80% or above. Each increase should be of 10dB and a new word list should be used. A person with normal hearing would be expected to score 100%. However, some people with hearing loss might only score up to, say, 70%.

Step 9 - Determine the client’s PB minimum score. Once you have determined the PBmax raise the presentation level by 10dB and test with a new word list. If the client’s score decreases, raise the presentation level by another 10dB and score again with a new word list. Continue this process until the highest presentation level for the audiometer is reached. The lowest score obtained is the PBmin and will be used to detect rollover.

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Step 10 - Repeat the test on the other ear, usually the worse ear. You may have to apply masking on the other ear, so remember to set the audiometer for speech noise for the non-test ear. Remember also that the worse ear will likely have a different initial presentation level.

Step 11 - Create a performance intensity function graph, or PI graph.

Step 12 – Calculate the rollover ratio.

Remember to tell the client

You will need to provide the client with test instructions. Proper instruction helps ensure that the test results are accurate and valid. There are a few important things to remember to tell the client:

• they will hear words through the earphones

• one ear (the better ear) will be tested first

• they need to repeat each word after they hear it

• if they are unsure, they still need to repeat what they think they heard

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• if they cannot make out the word, they need to let you know

• each word list will be at a different volume

• ignore any rushing sound in the other ear

• they need to tell you if they are not comfortable, and

• encourage the client to ask questions.

Here is an example of an audiologist instructing a client before a test:

“Okay Audrey, we’ve finished your audiogram now. We’re going to do some speech testing now. I’m going to put some words into your ears and I’d like you to repeat each word as you hear it. If you’re not quite sure or you think you missed a little bit, that doesn’t matter, I’d like you to repeat just exactly what you heard.”

Performance intensity function

A performance intensity function graph shows the percentage scores from the speech discrimination test (the performance) against the presentation levels (the intensity). This graph can provide useful information towards an accurate diagnosis.

A minimum of three word lists must be tested for each ear before creating the graph. This should be done at the initial presentation level, 20dB below and 20dB above. Where possible four word lists per ear are preferable.

In the example graph the blue line shows the normal increase in speech discrimination scores as the presentation level increases and soon, responses are 100% correct.

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Even with normal responses, you can still use PI function graphs to detect possible central lesions. Compare the PI graph of each ear to check if there is a significant difference between ears. ‘Significant’ means 20 to 30 percent difference and indicates that the client has a central lesion.

The red line also shows a normal response but shifted to a higher dB range indicating conductive hearing loss.

The purple line shows slight rollover, where an increase in presentation level does not have a corresponding increase in speech discrimination score.

The green line shows significant rollover. Note the difference between the performance at 70dB (PBmax) and at 90dB (PBmin).

RolloverRollo

ver occurs when a client’s speech discrimination score decreases even though the presentation level is increased.

The presence of rollover can indicate a lesion on the side of the brain opposite the ear with the roll-over, or 8th nerve lesions on the same side.

Calculating the rollover ratio can give you a better idea of which lesion type is present.

The formula for rollover ratio is: PBmax, minus PBmin, divided by PBmax. In the example PI function graph (the green line) the rollover ratio equals, 65, minus 35, divided by 65, which equals 0.46.

A rollover ratio of 0.4 suggests cochlear lesions.

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A rollover ratio of 0.45 or greater is a significant rollover and suggests 8th nerve lesions.

Cross-checking the results with the audiogramCross-checking the results obtained from speech audiometry tests with a pure tone audiogram can help validate your test results. This is particularly useful if you suspect a client is malingering or exaggerating their hearing loss. It is quite hard to fake a speech test to the same extent that you can fake a pure tone audiogram.

The three frequency average hearing level from the audiogram should closely match the speech reception threshold from the speech audiometry tests.

In the example results both the three frequency average hearing level and the speech reception threshold are 40dB. This helps validate the results and shows that the hearing loss is real.

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Explaining the results to the client

Here is an example of an audiologist explaining the results of a pure tone audiogram and speech audiometry tests to a client.

“Now that we’ve done all the testing, I need to explain to you what we’ve done. We have the audiogram here, that’s a graph of your hearing. The red circles demonstrate the levels at which we recorded your right ear, that’s the levels you can just hear sound and the blue crosses show the levels for your left ear. As you can see the left ear is a little bit worse than the right ear. Anything down to this 20 dB line would be considered within the normal limits, so your right ear is completely within normal limits, where we expect it to be. Your left ear is a little bit below that, and we would call this a mild to moderate hearing loss – and it’s a permanent type of hearing loss.

When we did the speech, we tested you at different levels and in the right ear you did very well all along. Everywhere we expected you to score. In the left ear, we had to turn the sound up a little bit for you to hear the same amount but you’re still hearing relatively well in that ear, as long as we turn up the volume for you. Sounds you particularly had problems with, were the high frequency sounds so for example the word fake you said fate, for chime you said time, that’s very common, so in this speech banana you can see that the high frequency sounds which are words like “th”, “ter”, “ker” are in the high frequencies and therefore, you’re having trouble hearing those in the left ear.”

Further testsFollowing speech audiometry testing you may conduct further tests include tympanometry and acoustic reflex testing. They are tests to see if the middle ear is functioning properly.

Tympanometry (or impedance testing) is conducted to test the volume of the ear canal, the air pressure of the middle ear, and the compliance of the tympanic membrane.

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Acoustic reflex testing checks the function of the stapedius muscle tightening the stapes. This is done by subjecting the ear to a loud noise to test the reflex function of the muscles.

Remember that your referral decisions should not be made on the basis of speech scores alone. Speech testing is part of a battery of hearing tests and all test results should be analysed in conjunction with each other.

CreditsPublished by the Centre for Learning Innovation (CLI).

CLI would like to acknowledge the following people and organisations who have contributed to the development of this resource:

Subject consultants:

Signe Peitersen

Bettina Turnbull

Reviewer: Peter Robinson

Location photographs taken at Connect Hearing, Lane Cove.

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Copyright© State of New South Wales, Department of Education and Training 2008

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