audiometry

Assessment of hearing


The basic audiometric assessment procedure is called pure tone audiometry. Before starting audiometric assessment you will have compiled a case history and possibly performed otoscopy.
Audiometric assessment is another way of saying hearing test. The word audiometry is also used to describe the testing of hearing.

When you perform audiometry you are finding the threshold of an individual’s hearing in comparison to the normal range.
When you find the thresholds you write them on an audiogram. An audiogram is a chart of the individual’s hearing.

There are many different types of hearing tests. Some words used to describe hearing tests are: subjective, objective, screening, diagnostic and electrophysiological.
Electrophysiological tests look at how different parts of the hearing mechanism function and include Auditory Brainstem Testing (ABR), Auditory Cortical Testing (ACR), Oto-acoustic Emissions (OAEs) and Electrocochleography (ECochG). These tests require special training to carry out and special skills to interpret the results. They are examples of objective tests, as the client does not tell you they have heard the sound. You will not be learning about these tests as they are beyond the scope of this course. You should, however, be aware of these tests. They are very useful tests and are often used when the client will not or cannot complete a hearing assessment.

Diagnostic tests involve determining degree and type of hearing loss. This is compared to screening tests, which are used to quickly determine if there is a hearing loss that requires further attention.

Subjective tests require the client’s cooperation. The client lets you know that they have heard the sound in some way.

This topic is concerned with pure tone audiometry. Pure tone audiometry is the most common type of hearing test. It can be used for clients from about 3 years of age. Pure tone audiometry measures thresholds for pure tone sounds. Pure tone audiometry is a subjective test. That is, you are asking the client to indicate when they have heard a sound.

To perform pure tone audiometry you need a machine called an audiometer. Audiometry should be performed in a suitable test environment.

The test environment

Audiometry is not valid if there is a great deal of background or ambient noise. Noise will affect hearing thresholds especially in the low frequencies. To reduce the effects of background noise you either have to find a very quiet spot or create a quiet environment.

Most permanent audiometry clinics create a quiet environment by using a sound treated room. Why call it a sound treated room? Isn’t it a sound proof room?

Do you remember where there is no sound? The only place is in a vacuum. We can’t survive in a vacuum so there are no assessment rooms that are truly sound proof. The closest we can get to a sound proof room is an anechoic room. These are rooms that are covered in foam absorption material with a suspended floor. These rooms are used for experiments but are too expensive and bulky for most clinics. There are anechoic rooms in Chatswood NSW belonging to Australian Hearing which are sometimes open to the public. These are the quietest places in the Southern Hemisphere.

Sound treated rooms vary in size. Some are big enough for only one person. Others are large enough to fit a desk and 3 - 4 people. They may be custom made or pre-fabricated.

The major problems with sound treated rooms relate to the noise that is made by ventilation and lighting. Just because a clinic has a sound treated booth does not mean it automatically meets the standard for background noise. The levels of noise inside a booth need to be checked, particularly if the lighting and ventilation are changed. If the level of ambient noise does not meet the Standard you may need to do something about reducing the levels.

Standard AS/NZS 1269.4 – 1998: Occupational Noise Management: Auditory Assessment published by Standards Australia provides the levels of ambient noise that are acceptable for audiometry. You will see different levels for different types earphones. You will need to use a sound level meter to check the levels of ambient noise in a test environment.

If the room is large enough, audiometry may take place inside the booth. Therefore, the audiometer and clinician would be in the booth with the client. If the room is not large enough, only the client would be seated in the booth.

Seating the client

Whether or not the clinician is in the booth with the client it is best if you can see the client. Booths where the clinician sits outside usually have a window through which the clinician can watch the client.

When the client and clinician both sit inside it is a little more difficult for the clinician to ‘hide’ what they are doing. Some clinicians prefer to seat the client so that they have their back to the audiometer. This is so the client is not able to see the audiometer and respond to something other than auditory stimuli. That is, the clinician does not want to cue the client by their actions that the sound is being presented.

A compromise between this and staring directly at the client is to turn the client side on to the audiometer. You can still watch the client without feeling uncomfortable. Some clinicians suggest to the client that they close their eyes so that they can concentrate better. It is best to be able to see the client’s responses to the sounds because you are often able to see indications from the client when they are not sure they have heard the sound. You can then reassure the client that they did indeed hear the sound.

The audiometer

The machine needed to perform audiometry is the audiometer. It would be useful to have a diagram of the audiometer nearby for the next part of the learning guide. You might like to draw your own diagram of an audiometer and label the parts, including the frequency and decibel range.

What does the audiometer do?

The parts of the audiometer give you clues to answer this question.
• The frequency dial: The audiometer generates pure tones at various frequencies. Most audiometers will generate the following frequencies (in Hertz or cycles per second): 250, 500, 750, 1000, 1500 ,2000, 3000, 4000, 6000 and 8000.
• The decibel dial: This changes the intensity level of the frequencies in 5dB steps. The decibel scale is in Hearing Threshold Level. Most audiometers can change the level of sound from 0dBHTL to about 100dBHTL for air conduction testing. For bone conduction testing the upper limit is about 60dBHTL.
• Transducer: On most audiometers TDH39 or 49 earphones are used for air conduction testing and are labelled for the right ear and the left ear. Usually the earphones are coloured red and blue. Red is for the right ear and blue is for the left ear. These may be inside circumaural enclosures that will help with ambient noise levels. You may also be able to use E.A.R. 3A or 5A Insert earphones as an alternative.
• Bone conduction vibrator: This is used for bone conduction testing.
• An interrupter switch: This is the name often give to the switch or button used to present the sound.
• An output selector switch: This switch selects the right or left ear or the bone conductor.
• A patient response button: When pressed an indicator light shows the clinician that the client has heard the sound.

What is the maximum output of the audiometer?

Audiometers have a maximum level at which you can no longer increase the intensity. This will vary between audiometers and will depend on what frequency is being used and whether you are using the earphones or the bone conductor. Some audiometers have the facility to add an extra 20dB if you select it by pressing the relevant button. You need to be careful though to make sure you know whether the audiometer automatically shows the increase or not and whether you have turned it off.

If the client does not respond to the maximum level then it is the convention in audiometry to indicate this level. You would do this by drawing the relevant symbol at that level with an arrow pointing down.

The smaller audiometers have fewer features and are usually called screening audiometers. The larger audiometers with more features are called diagnostic audiometers. Diagnostic audiometers are often connected to other machines, e.g. a tape or CD player for speech testing, a computer for recording information.

There are also automatic audiometers. They have an automatic testing protocol. These are often used in screening programs. This guide will focus on manual audiometry. Automatic audiometry has limited uses and does not allow the flexibility you need for testing most clients.

So, what is the answer to the question: What does the audiometer do?
The audiometer is a machine for determining hearing thresholds to pure tone sounds.

You may be able to do many other types of assessments with an audiometer but this is the basic purpose of all audiometers.


Hearing thresholds

The word threshold means a starting point or beginning of awareness of a stimulus. When we talk about hearing threshold, we are talking about the point that there is an awareness of sound.

What is a hearing threshold?

In pure tone audiometry, threshold is the point at which a pure tone can just be heard 50%, half, of the time. In practice, a hearing threshold is the lowest intensity of a tone at which 2 out of 3 responses are observed.

How is a hearing threshold observed?

In pure tone audiometry the response to a sound is observed when the client indicates they hear it. This indication could be by raising the arm, hand or finger, tapping the table or by pressing a button. The client will respond to the sounds depending on the way you have instructed them.


Instructing clients

Instructing the client is extremely important. To achieve the best results possible you must instruct the client well.
Your client must be clear about what is expected of them and what will happen.

Your instructions should be clear and brief, letting the client know what to expect and how to respond. It is often useful to use gestures. The instructions must be understood.

The client needs to understand:
• they are listening for very soft sounds
• they have to respond every time they hear the sound
• they will be hearing different tones
• the tones will be heard in one ear and then the other ear
• how to let you know they have heard the sound.

Have you heard a clinician instructing the client? Keeping the above points in mind and what you have observed, how would you instruct the client?

One way of instructing the client is to say something like:
‘You will be hearing a series of beeps and buzzes, first in the right ear and then in the left. As soon as you hear the sound, no matter how soft it is, let me know by pressing the button. Like this. (indicate how to press the button).’

The instructions should be kept simple and brief or your client might forget what you want them to do before they start.

The instructions should not be vague. If you say, ‘Press the button when you think you hear a sound’, the client may be unclear about when to press the button.

If you do not have a patient response button, you change the instructions so that the client is clear about what you want them to do. A gesture showing the client what to do is often helpful.

This type of instruction is suitable for adult clients and older children. Most children can follow these instructions from about 8 years of age. Children under this age require special instructions. Play audiometry is suitable for children from about 3 years of age until about 8 years of age. Many children over 8 years of age will prefer to play a game to pressing the button so it is best to give them a choice. Play audiometry will be discussed later.

Have you ever had a hearing test? If not arrange to have an assessment of your hearing. While you are having the assessment make a mental note of how you are instructed, what types of sounds you are listening to. Most of all you will come to realise that having an audiometric assessment involves a lot of concentration.

Once you have instructed the client it is time to place the earphones.

Placing the earphones

Earphones are used to test air conduction hearing thresholds. Air conduction will be described very soon.

Free field hearing testing is also used for specific reasons. Free field hearing testing is done without earphones. That is, the client sits in a sound treated room where a free field has been created and a sound is generated through a speaker. The client responds to this sound which is often a warble tone. A warble tone is based around a pure tone and includes the frequencies around it. For example, a warble tone at 1000Hz would include frequencies from 950 to 1050Hz. Warble tones avoid the problem of creating standing waves, i.e. dead spots.

Primarily, free field testing is used for children who are less than 3 years of age. There are some specific speech tests that are conducted free field. It was, in the past, also used for testing aided thresholds. That is, hearing benefit obtained from hearing aids. Although some clinics may still have this facility, most have now switched to other methods of testing aided thresholds. You will learn more about this in the rehabilitation learning guide.

You cannot use just any earphones for audiometric assessment. They must be a special kind of earphone. Australian and International standards set out what earphones can be used. Most audiometers have TDH 39 or TDH 49 headphones.

You must use the earphones that belong to the machine that you are working with. That is, you must never swap earphones between machines. This is because it will effect the calibration of the audiometer.

The only exception to this rule is if you would like to use E.A.R.-3A or E.A.R.-5A Insert Earphones. They are sometimes referred to as tube phones. Insert earphones may not be available in all clinics as they are not routinely supplied with an audiometer and are purchased separately. They have disposable foam tips that are inserted in the ear canal. These tips are attached to the insert earphones. Some audiometers will allow you to have more than one set of earphones attached at the same time and you can select which to use. More commonly, you would remove the headphones from the two jacks that are inserted into the audiometer and replace them with the insert earphones. You will need to check whether there are any correction factors.

Insert earphones have two advantages over the normal earphones. They are lighter with no band over the head. The second advantage is that they provide better results if there is some background noise. The disadvantage is that they are more invasive than normal earphones and you MUST perform otoscopy before inserting the foam tips. You would not use them if there were discharge in the ear canal or excessive wax present. For more information about the insert earphones you can look at the website of the company that developed them, Etymotic Research. The web address is www.etymotic.com.

The special earphones needed for air conduction audiometry are called TDH-39 or TDH-49. They may be used on their own or placed inside special cushions that are called circumaural or supra-aural cushions. They assist in making the test environment suitable for audiometry. That is, it is possible to have higher levels of ambient noise if you use circumaural cushions.

Before putting on the earphones, ask the client to remove glasses, i.e. spectacles. You should also ask the client to remove earring/s if you suspect that they might dig in and cause pain or if they look like they could be bent out of shape by the pressure of the earphones. Make sure the client doesn’t forget to put them back on!

The earphones must be put on carefully. That is, place the diaphragm of the earphones directly over the opening of the ear canal and the band sits across the top of the head. The diaphragm of the earphones looks like small circles in a larger circle.

If the earphones are not placed directly over the opening of the ear canal, hearing thresholds could appear worse than they really are. This effect is most obvious at 6000Hz.

Earphones can cause collapsed canals. This is where the canal is forced shut due to the pressure of the earphones. You can check for the possibility of collapsing canals during otoscopy. While looking at the pinna, if you push gently on the cartilage you can see if the ear canal opening seems to be closing. When you look in the ear canal the skin may seem very soft and loose, increasing the likelihood of the canals collapsing with pressure.

If the canals collapse, hearing thresholds for air conduction will appear worse than they actually are. To avoid collapsing canals you can ask the client to hold the earphone gently against the pinna. The client’s arm may get tired so it is best to have the client lean their elbow on the arm of a chair or on the top of the desk. This is only necessary when you suspect the canals are collapsing. You could also use insert earphones if they are available.

Now that the earphones are placed correctly on the client it is time to start the audiometric assessment. The earphones make it possible to perform air conduction audiometry.

Air conduction

Which ear do you test first? Do you think it matters which ear you test first?

The convention is to start testing the right ear first unless there is a difference between the ears in which case you start with the better ear. Complete all frequencies for one ear and then switch to the other ear and test all frequencies.

If the ears are the same, it does not matter which ear you start with. Some clinicians prefer to test both ears at each frequency before proceeding to the next frequency.

But how do you know which ear is the better one before you do the test? You may not know, but it is likely that the client does. It often happens that the client will tell you or at least give you hints during the compiling of the history. If you prefer you can ask them, ‘Do you think your hearing is pretty much the same in both ears?’

At this stage, with the majority of your clients you have compiled the case history, performed otoscopy, the client is seated in the sound treated room with the earphones placed correctly and the audiometer is switched to the right ear. Now what? Now is the time for the clinician to sit down and start testing.

The first frequency to test is 1000Hz. Most clients find this frequency fairly easy to hear. A common sequence is as follows, assuming both ears are likely to be approximately the same:


Right ear


Left ear
1.
1000Hz

8.
1000Hz
2.
2000Hz

9.
2000Hz
3.
4000Hz

10.
4000Hz
4.
8000Hz

11.
8000Hz
5.
1000Hz

12.
1000Hz
6.
500Hz

13.
500Hz
7.
250HZ

14.
250HZ

These frequencies and 125Hz are the octave frequencies. Most clinicians do not test 125Hz unless there is a specific reason; e.g. client has a profound hearing loss. Sometimes the mid-octave frequencies are also tested. The rule for testing mid-octave frequencies is:
you test mid-octave frequencies when there is a difference between octaves of 20dB or more.

The mid-octave frequencies are 750Hz; 1500Hz; 3000Hz and 6000Hz. Some audiometers have extra frequencies above 8000Hz as well but you will need special headphones to test these frequencies.

There is no reason not to test mid-octaves. Many clinicians prefer to include the testing of 3000Hz and 6000Hz. Many clinicians do not test at 125Hz and 250Hz. Depending on the purpose for the audiometric assessment various frequencies will be tested. In some cases you must test mid-octave frequencies particularly if the assessment is for work related purposes.

In the above recommended sequence, 1000Hz has been rechecked. This is not always done. The reason for checking 1000Hz is to see if the client is consistent. That is, was the second response similar to the first response? If not, why not? Sometimes there is a training effect, i.e., the client is now aware of what is expected of them and responds better. In this case, take the better response and quickly recheck the other thresholds for improvement. If the client’s second response is significantly worse: Have they lost concentration?; Are they deliberately trying to make it appear that their hearing is worse?; Have they forgotten what you wanted them to do? Try encouraging the client to respond to the very soft sounds and to keep concentrating for a little longer.

What have you just tested?
Did you say you have tested the client’s hearing? That is partially true. You have tested one aspect of the client’s hearing. You have completed the air conduction component of pure tone audiometry. If you are doing a screening test, that may be all you need to do.

Test-retest variability

Test-retest variability is the minor differences that occur between tests. It is accepted that if there is 10dB difference between results then this is not a true difference and relates to test-retest variability. In other words, it is not considered to be a real difference until there is a variation of 15dB or more.

But what does it all mean?
Air conduction audiometry assesses the ability of the entire hearing mechanism to respond to pure tones. That is, the sound passes through the outer, middle and inner ear and up the neural pathways to the cortical region of the brain. If any part of the hearing mechanism is not operating properly the hearing will be affected. So when you do air conduction test and it shows a hearing loss you do not know where the site of lesion is. ‘Site of lesion’ is the terminology we use to describe the place of the breakdown of the hearing mechanism.

Symmetry

The hearing is considered to be the same in both ears if the results of the right ear and left ear at each frequency fall within 10dB of one another. That is, there is no test-retest variability. This is referred to as symmetrical.

There may be a difference between the ears, i.e. asymmetry. This may mean that the responses come from the better ear. You may need to perform further testing before you can explain the hearing status of that client. This will be explained in the section on masking in the guide called Assessment B.


Bone conduction


The next step of the hearing assessment is bone conduction. The results from bone conduction testing when compared to air conduction testing will provide some information about site of lesion.
Essentially, bone conduction is sound transmitted to the inner ear by the bones of the skull.

To test for bone conduction you need a bone conduction vibrator, also called a bone conductor. This is placed on the mastoid process of the temporal bone, sometimes simply called the mastoid bone. That is, on the bony part behind the pinna. The bone conductor should not be placed on hair.

On very rare occasions the bone conductor is placed somewhere other than the mastoid. The centre of the forehead is the most likely place. However, in Australia most clinicians will only perform bone conduction placed on the mastoid.

For the bone conductor to work properly there must be a certain amount of pressure applied to the mastoid, that is why the band of the bone conductor is so springy. You must never over stretch the band so that there is little or no pressure against the head. The client may experience a little discomfort. You could say to the client: ‘This may feel a little tight, but it won’t be on for long. It has to be that way for the test.’

It takes a lot of energy to drive the bone conductor so audiometers are unable to produce high intensity levels for bone conduction testing. Most audiometers cannot make the sound louder than about 70dBHTL.

How does bone conduction work?

Bone conduction is a very complicated process. When the bones of the skull vibrate there are at least three things happening. These are:
1. as the skull moves, the bones of the middle ear do not start moving immediately, i.e. they exhibit inertia, causing the stapes to move in and out of the oval window;
2. the bones of the skull distort and cause the cochlea to distort, this then causes activity that is the same as the activity that would have been created by air conducted sound;
3. the vibration of the skull causes the air in the ear canal (EAM) to vibrate, some of this vibration is passed on to the eardrum (TM).

Theoretically the sound generated by the bone conductor bypasses the outer and middle ear. That is, the sound generated by the bone conductor goes directly to the inner ear. Responses obtained by using the bone conductor are considered to be for the inner ear and neural pathways. However, there are effects from the middle ear.

The effect that you will come across when performing audiometry is called the Carhart’s notch. This effects the level of the bone conduction result at 2000Hz.

Otherwise, you can think about bone conduction responses as being unchangeable by the outer and middle ear. And that the responses you achieve by performing bone conduction are a representation of the hearing level at the cochlear level.

Which ear do you test with a bone conductor?

In theory, the sound generated by the bone conductor reaches both cochleas. That is, when you test with a bone conductor it doesn’t matter which ear you put it behind, the sound will be transmitted to both sides. In practice, there may be a slight difference. However, you cannot say, that when you put the bone conductor behind the right ear you are only testing the right ear or when you put the bone conductor behind the left ear you are only testing the left ear. This is a very important point to remember for later when you learn about masking.

Bone conduction is normally performed without covering the pinna. That is, when you test for bone conduction you remove the earphones you used for air conduction. So, if you were thinking of saving time and effort by placing the bone conductor and the earphones on at the same time - think again! There is a very good reason not to cover the ears when testing bone conduction. It is called the occlusion effect.

During bone conduction testing, if the ear is covered, the occlusion effect increases the loudness of low frequency sounds i.e. 1000Hz or lower.

One sequence you could follow to test bone conduction is as follows:



Bone conduction
1.
1000Hz
2.
2000Hz
3.
4000Hz
4.
500Hz


If you tested other frequencies between 500Hz and 4000Hz for air conduction, you could also test them for bone conduction. Most audiometers do not produce bone conduction above 4000Hz. If bone conduction is available over 4000Hz you will have to check to see what calibration figures were used. If the audiometer has not been calibrated to the Australian standards then you can only use the figures as a guideline for yourself.

Many clinicians do not test bone conduction at 250Hz because of the tactile nature of this sound. That is, it is often felt rather than heard so the information you get from doing bone conduction at 250Hz is treated with caution. In other words, you’re not always sure how useful the result is.

Can bone conduction levels be worse than air conduction levels?
The short answer to this question is no. However, it is possible that the bone conductor has not been placed on the mastoid very well. If this happens it is possible that the results may be effected. It may also occur if the client is not completely cooperative in the test situation and therefore would be considered an indicator that the client’s motivation is not to respond to threshold. It could also mean that the person has lost concentration. If the response is within 10dB then it is not considered a difference so you may just be showing a test-retest variability.

Audiometric Weber

The forehead setting for the bone conductor is sometimes used with a test called the Audiometric Weber. In this test the client is asked to point to which ear the sound is heard. The results are noted as right, left or central. Central means the client couldn’t hear the sound in only one ear and the sound seemed to be coming form somewhere else. It is usually only done at 1000Hz, 500Hz and 250Hz and a little above threshold as this is the easiest way to hear the sounds.

It is not a common test now but was done quite routinely in the past. It is based on tuning fork tests that an ENT Specialist might use. It was used to help the clinician when there is some doubt about whether there is a middle ear component to the hearing loss.

Carhart’s notch

Carhart’s notch is where the bone conduction is affected at 2kHz by the condition of the middle ear. It is often seen when the client has otosclerosis, a common cause of conductive hearing loss in adults. If the client undergoes successful surgery, it is likely that the bone conduction at 2kHz will improve. Most of the time, though, you would not expect the bone conduction results to vary before and after surgery unless there has been an effect on the cochlea.

When you have tested air and bone conduction you can start to describe the degree and type of hearing loss. But how did you actually get the results?

The basic audiometric assessment method is called the Hughson-Westlake technique.


The Hughson-Westlake technique

When you are performing audiometric assessment you can use an ascending technique or a descending technique or a combination.

The words ascending and descending mean going up and going down. When applied to audiometry, they relate to the clinician increasing the level of the sound or decreasing the level of the sound to determine the client’s hearing threshold.

The Hughson-Westlake technique is the most common testing technique used. It is more correctly known as the modified Hughson-Westlake technique as the original method has been changed slightly.

It is an ascending method and is sometimes referred to as the ‘up 5dB -down 10dB’ procedure.

The first presentation is reasonably loud e.g. 60dBHTL. If the client responds, the intensity is reduced by 10dB until there is no response. It is then increased by 5dB until there is a response. The intensity is again reduced by 10dB until there is no response and then increased by 5dB until there is a response.

If the initial sound is not responded to, increase the level of intensity by 5dB until the client responds.

Sometimes starting at 60dBHTL is too loud. If the client is likely to have normal or near normal hearing it would be better to start at 30dBHTL. Occasionally it is best to start at 0dB and increase from there.

The threshold is determined when there are 2 out of 3 responses. Only the responses on the ascending series are taken into account, which is why it is called an ascending technique.


For example, in the right ear at 1000Hz: 60dBHTL response
50dBHTL response
40dBHTL no response
45dBHTL response
35dBHTL no response
40dBHTL response 1st
30dBHTL no response
35dBHTL no response
40dBHTL response 2nd
30dBHTL no response
35dBHTL no response
40dBHTL response 3rd


The threshold of hearing at 1000Hz in the right ear is 40dBHTL.


Summary

1. Seat the client in the sound treated room.
2. Instruct the client clearly.
3. Place the earphones/bone conductor.
4. Start at 1kHz at a level that will easily be heard, try 60dBHTL or 30dBHTL in the right ear or the better ear.
5. If the client responds decrease by 10dB.
6. If the client does not respond increase the sound by 5dB.
7. Obtain 2 out of 3 responses at the same level in an ascending manner.
8. After 1kHz is finished, test 2kHz, 4kHz, 8kHz, recheck 1kHz then do 500Hz and 250Hz. If there is a difference between octaves of more than 20dB test the inter-octave frequencies.
9. Repeat for the other ear.
10. Repeat for bone conduction.


dBHTL
Do you remember the definition of dBHTL?

Decibels Hearing Threshold Level is based on the average hearing level of a large group of young adults with no history of hearing problems where 0dBHTL is the average hearing threshold.

It is very important for you to fully understand what this means. If you have forgotten or can’t explain it, now is the time to go back and review this concept.


Appropriate techniques for different clients

The Hughson-Westlake is not the only technique used. However all audiometric assessment methods use an ascending or descending technique or a combination of the two.

Many clinicians prefer an ascending technique in which the starting level is very soft, 0dBHTL is appropriate for clients with normal or near normal hearing. The level is increased until there is a response and then follows the ‘down 10, up 5’ process of the Hughson-Westlake. Many clinicians feel this encourages the client to respond at very soft levels and is a quicker assessment technique. This may be suitable for a client who is not motivated to respond to soft levels of sound.

One combination method is sometimes called bracketing. Initially the clinician increases the sound until the client responds. A louder sound is then presented and the sound is decreased until the client stops responding. A number of series are used to establish the softest intensity level at which the client responds to 2 out of 3 presentations.

There are techniques where the client controls the level of presentation. One of these is called Bekesy audiometry. This was a common technique until the 1980s. It is an automatic technique. The client keeps their finger on a response button while they hear the sound and remove it as soon as the sound stops. There are now other automatic audiometers that you may use in certain clinics. Automatic audiometers do not offer the flexibility of adjusting your testing method to suit the client.

Screening tests are often used to check large populations quickly to highlight problems that should be followed up. For example, children in schools may be screened. The clinician would decide on the pass/fail criteria. Usually, children would be expected to respond at 20dBHTL at 500Hz, 1000Hz, 2000Hz and 4000Hz for both ears. In this type of screening test only these sounds would be presented. Children who do not respond at these levels would then be assessed more thoroughly.

Take the opportunity whenever you can to observe different methods that clinicians use and try to find out why they prefer those methods. With experience you also will respond to different clients to help them complete the audiometric assessment.

The pattern of presentations

So far we have talked about the sequence of presenting the frequencies and the intensity of the pure tones you want to test. You also need to know how to present the sounds so that the client does not know when to expect to hear them.

That is, you must present the sounds randomly or the client may respond to the patterning of your presentations rather than hearing the sound. This is particularly important when testing children.

When you perform a hearing assessment you want your results to be valid. A valid response is one which measures what it intends to measure. When you are testing hearing you want to be able to measure the client’s hearing, not their ability to guess when you are about to present the sound.

When you begin clinical practice you might find it helpful to count to yourself between presentations. For example,
present 1st sound, count to 5
present 2nd sound, count to 9
present 3rd sound, count to 6
present 4th sound, count to 3, etc.

Another way of saying this is, you must vary the inter-stimulus interval randomly.

One mistake that is often made is that the clinician presents the sounds too quickly, i.e., they do not allow enough of a break between the stimuli. This often confuses the client and leads to false positive responses and false negative responses.

A false positive response occurs when the client indicated they have heard a sound when none was presented. A false negative response occurs when the client does not indicate they have heard a sound even though they have.

If you present the sounds too quickly the client may not respond because they think it is the same sound. Or they may keep responding because they are anxious they will miss a sound. Some clients say they think they are hearing an echo.

It is better to allow slightly longer inter-stimuli intervals. If the client does start to respond haphazardly, slow down. You may even need to stop, give the client a quick break and reinstruct. So you can see it does not save time to present the sounds quickly. It often takes a lot longer.

If you take too long between presentations, however, the client may begin to think there is something wrong. Clinics rarely have unlimited time for a hearing assessment so you will have to learn to find the correct balance between being too quick and being too slow.

Length of presentation

The length of presentation should be between 1 and 2 seconds. If you say ‘one thousand and one’ to yourself while holding the interrupter, the tone will be on for long enough for the client to hear.

If the tone is too short, the sound will have to be louder for the client to hear it. Keeping the tone on longer than about 2 seconds makes no difference to hearing the tone.

Some clients have difficulty detecting the pure tone because of tinnitus. That is, their own head noises make it difficult for them to know when the tone has been presented. For these clients, if you present the tone as a pulsed tone it will help them. A pulsed tone will sound like a ‘beep beep’ presentation and each beep should be about 1 second in duration. Some audiometers have a pulsed setting that you can use. Some clinicians use a warble tone – this is acceptable if the tinnitus is so problematic that the client cannot do the test any other way.

If you do vary the test technique it is worthwhile to make a note of what you did and why it was done. For example: ‘Mr X had trouble with 4kHz because of tinnitus so I used beep beep presentation’.

Dealing with clients who can’t / won’t co-operate
One of the aims of performing audiometry is to achieve reliable responses. A reliable response is one that can be repeated. So a reliable audiogram is one that can be repeated at any time by any suitably trained clinician using calibrated equipment anywhere in the world.

When you first meet your client you assume that they are willing and motivated to do their best. You also presume they are able to maintain the level of concentration necessary to complete the test. These client related conditions will assist you to achieve a reliable audiogram.

You should start every audiometric assessment with the attitude that your client will participate fully with you. It is not common that your client is not motivated to do the best they can. If you feel the client should be doing better, give them the benefit of the doubt, they may not have understood exactly what you wanted them to do. Try reinstructing the client.

Some clients genuinely believe that you cannot possibly want them to respond to the very soft sounds so you may need to explain the procedure to them.

Audiometry is affected by the client’s ability to concentrate. The assumption is that clients are able to maintain the level of concentration necessary to complete the test. If the client is not well or is unable to maintain the level of concentration needed then your results will be affected. You should make a comment in your file notes. For example: ‘Mrs T told me she was unwell today and could not concentrate well. Will book her in for a quick retest in 2 weeks time. I have asked her to cancel the appointment if she is still unwell and make another when she is feeling better’.

If you feel that it is unlikely that the client will be able to concentrate for long enough you will have to decide what is most important. Usually the frequencies that are tested first in this situation are 1kHz and 4kHz. You may have to do a test over a number of appointments to get a full audiogram.

It does not happen very often but occasionally you will be required to test a client who is not motivated to respond to the softest sounds they can hear. You may get some indication from the case history. For example, they might tell you about the extreme difficulty they are having at home because they do not hear well yet have no problem responding even when you talk to them from behind their back.

These clients usually have a motivation. Some clients hope to receive workers compensation. Some clients simply want a little attention from their families. Whatever the motivation, these clients need special handling.

With experience, you will get a general impression of overall impairment before you start the assessment. A severely or profoundly hearing impaired person who has no hearing aid will not respond without being able to see you. A client who answers questions appropriately when you are standing behind them, i.e., they can’t see your face, and you are using a soft voice is unlikely to have more than a mild hearing loss.

With many of these clients an ascending audiometric technique is more appropriate. Some will simply respond to extra encouragement and kindness. Speech testing may also help you in this situation. You will learn a lot by watching experienced clinicians dealing with these clients.

You will have to make a decision about the reliability of the responses. You can only write the best response the client has given on the audiogram. If the client would not or could not cooperate you cannot say that you know the client’s hearing is better and therefore, note the threshold as better on the audiogram. What you can do is write the best responses on the audiogram and write something e.g.: ‘client said he was doing the best he could’. Be extremely careful what you write, it is best to describe behaviour or write comments that the client made. You must never make derogatory remarks or personal comments about clients e.g.: ‘Mr X was being a real pain today’, ‘client acted stupid’ etc.

If you are concerned about testing clients you can ask your supervisor if they would like to complete the testing.

Certain tests do not require the client’s cooperation. These are called objective tests because the client does not tell you they have heard the sound. Electrophysiological tests are objective tests. These include Auditory Brainstem Testing (ABR), Auditory Cortical Testing (ACR), Oto-acoustic Emissions (OAEs) and Electrocochleography (ECoG). These tests require special training to carry out and special skills to interpret the results. You will not be learning about these tests as they are beyond the scope of this course. However, you may consider referring clients to a clinic that performs these tests particularly if there is a legal reason for obtaining an accurate audiogram.

Play audiometry

When testing children, keep in mind that you may not be able to keep their interest for long enough to complete the audiogram unless you incorporate play into the assessment.

You would tell the child at the beginning that you want them to play a listening game. Show them what you want them to do, e.g., put a peg in a bucket, a ring on a pole, and ‘shape’ the response. That is, train the child to do the activity to a sound before putting on the earphones.

Then work as quickly as possible to get the results without working so quickly that the child gets confused. When working with children you adjust your testing technique to obtain the most important information first.

A typical sequence for working with children is as follows:



Air conduction: Right ear


Air conduction: Left ear
1.
1000Hz

2.
1000Hz
3.
4000Hz

4.
4000Hz
5.
2000Hz

6.
2000Hz
7.
500Hz

8.
500Hz

Bone conduction



9.
1000Hz

10.
4000Hz
11.
2000Hz

12.
500Hz

This sort of technique is appropriate for children from about 2 ½ years of age to about 8 years of age. The most variable age group is children aged 2 ½ to 3 ½ years. You can test some in this age group successfully but not all. It is not possible to predict which child will work with you and which will not. Some children will do very well until you try to put the earphones on and will object to them.

Older children may not like to play ‘baby games’ so you may need to find something more appealing to the older age groups. A child of 7 may like to draw ticks on a page or use self inking stamps to make a pattern. A child of 8 may like to feel grown up and press the button like an adult. Children are usually very happy to tell you what they would like to do. However, you need to be cautious about asking the child a yes/no question when a no answer is unacceptable. For example, ‘Will we go in here?’ (i.e. to the test booth). If the child says no, what are you going to do? You could ask ‘Will we play the peg game or the tower game?’, i.e. offer them alternatives.

It is better to allocate a little extra time for testing young children so that you have sufficient time to get to know them and to instruct them. It is common for a young child to forget what they have to do during a test so you may need to reinstruct them.

Tactile responses

Some sounds generated by the audiometer are sufficiently loud to produce a perceptible vibration. That is, the client responds to a sound not because they heard it but because they felt it. Another way of saying this is that the client is responding to tactile stimuli. This happens most commonly to low frequency sounds generated by the bone conductor. Many clinicians do not test for bone conduction below 500Hz because of the likelihood of this happening.

If a client responds only to air and bone conducted sound below 1000Hz at the maximum levels of the audiometer it is possible that they are responding to tactile stimuli.

Some clients are unable to tell you whether they heard the sound or felt it. However, you should ask. If the client informs you that they felt it, you can report that the responses were ‘tactile’.

These responses are still valid for the audiometric assessment and, therefore, you can note them on the audiogram.

The following are likely to be tactile responses:

Air conduction: 250Hz at 90dBHTL
500HZ at 100dBHTL
1000Hz at 120dBHTL
Bone conduction: 250Hz at 40dBHTL
500Hz at 70dBHTL.


Do not think that every time you get these responses they are tactile. They may be auditory responses, however, if these are the only results you get, you should ask the client: ‘Did you hear those sounds or did you feel them?’

The audiogram

The audiogram is the chart of the client’s hearing. As you test them you will write down the results. The audiogram looks like this:
audiogram.png

You can see the octave frequencies are written across the top. The mid-octaves are written on the lines between them. On the side is the intensity level in decibels Hearing Threshold Level. The lines are in 10dB steps so if a response is obtained at 45dBHTL it would be written between the 40 and 50 lines.

The only symbols in audiometry that are internationally agreed on are for unmasked air conduction. The ‘o’ is used for the right ear and the ‘x’ is for the left ear.

Unmasked bone conduction results may be shown as ‘ ’ or ‘<’ for the bone conductor placed on the right mastoid or ‘>’for the bone conductor placed on the left mastoid.

When the maximum output of the audiometer has been reached and the client has still not indicated they have heard the sound an arrow is added to the symbol, e.g., .

By convention the results for the right ear are joined by an unbroken line and the left ear by a dashed line.

These symbols are for unmasked audiometry, masking will be discussed in another learning guide and is necessary when there is a difference between the ears.

Whatever symbols you use, they should be written on the audiogram. Most audiograms have the symbols printed on them along with a space for the date, client’s name, audiometer used and clinician’s name.


Type and degree of hearing loss

The audiogram will give you the information to describe the hearing in terms of degree and type. The type of hearing loss requires you to have done both air and bone conduction testing.

The degree of hearing loss is described as mild, moderate, severe or profound. If responses are recorded at less than 25dBHTL the hearing is within the normal range.
Mild hearing loss 25 to 45dBHTL
Moderate hearing loss 50 to 70dBHTL
Severe hearing loss 75 to 90dBHTL
Profound hearing loss more than 90dBHTL.

The most common way to describe a hearing loss is to look at the results between 500Hz and 4000Hz. This is not a strict guideline, though, as there are many situations that the levels of the other frequencies are very important.

It often happens that the hearing loss is in more than one region. When this happens you can join the degree of loss. For example, mild-moderate, severe - profound etc.

The type of hearing loss is described as sensorineural, conductive or mixed. These terms define the site of lesion, i.e., where the breakdown in hearing occurs. In a conductive hearing loss, the breakdown in hearing occurs in the outer or middle ear. In a sensorineural hearing loss the breakdown in hearing occurs in the cochlea or beyond. A mixed hearing loss involves a combination of conductive and sensorineural impairment.


On the audiogram:
• a conductive hearing loss is shown by the bone conduction within the normal range and the air conduction outside of the normal range
• a sensorineural hearing loss is shown by the bone conduction and the air conduction being equal and outside of the normal range
• a mixed hearing loss is shown by the bone conduction and the air conduction being outside of the normal range but the bone conduction results are better than the air conduction, i.e. there is an air-bone gap.

Air and bone conduction are considered to be equal if they are within 10dB of one another. In other words, if there is a gap between the air conduction and the bone conduction of 15dB or more it is considered that there is an air-bone gap. Bone conduction should never be worse than air conduction. If it is, check that you have placed the bone conductor on properly.

There is another type of hearing loss that the audiogram cannot define. The audiogram can only provide information about the peripheral hearing mechanism, i.e., the outer, middle and inner ear. The audiogram cannot provide information about a processing disorder or a problem at the cortical level. Clients with a processing disorder display communication difficulties beyond what is expected for their degree of hearing. It is often related to a problem with the transmission of the sound from the cochlea to the brain. If you suspect that the client has a processing disorder you will need to refer your client to a clinic that performs the relevant assessment.

Other descriptions are used for the audiogram. Sometimes, the clinician will include a comment about the slope of the audiogram. It is common for the audiogram to gently slope from the low frequencies to the high frequencies and so this is not usually commented on. A comment is usual if the audiogram is upwardly sloping or if it is steeply sloping.

You can describe each ear separately or it the ears are the same you can describe them together. Monaural means one ear and binaural means two ears. Unilateral means one sided and bilateral means two sided. If the ears are different you can define the hearing loss as asymmetrical or if they are the same you can say the hearing loss is symmetrical.


The 3FAHL

The three frequency average hearing loss (3FAHL) is often used to describe hearing loss. To calculate the 3FAHL, add the decibel levels at 500 1k 2k for one ear and then divide by 3. The figure can be rounded off to the nearest multiple of 5. For example, the responses for the right ear are:
500Hz 30dBHTL
1000Hz 40dBHTL
2000Hz 55dBHTL
30+40+55=125
125 divided by 3 = 41.66
rounded off to 40dBHTL

The 3FAHL may help you to decide the degree of hearing loss. The 3FAHL is also used in speech audiometry so it is worthwhile to take some time to practice looking at some example audiograms and working out the 3FAHL.

Some examples of audiograms with their descriptions


Audiogram 1:
Pure tone audiometry shows hearing is within the normal range for both ears.
In this audiogram bone conduction testing has been done but many clinicians would not do it. It depends on why the test is done whether you would do the bone conduction testing. It is more common to test for bone conduction if the doctor is worried about middle ear problems. If this test were done for screening purposes then you would probably not do bone conduction.
audiogram1.png

Audiogram 2:
Pure tone audiometry shows hearing is within normal limits but there is an air-bone gap.
In this circumstance hearing is within normal limits but there is an effect on the hearing by something in the outer or middle ear. That is, there is a conductive element.
We do not know if both ears are affected as the bone conduction result may relate to both ears or only the better one. Further testing is needed, i.e. masking.
audiogram2.png
Audiogram 3:
Audiogram shows a mild hearing loss in both ears, conductive in nature in at least one ear but probably both.
When you learn about masking you would perform masking for this client or make a comment about why masking could not be done.
audiogram3.png

Audiogram 4:
Hearing test today shows a mild-moderate sensorineural hearing loss.
Remember if air and bone conduction results are within 10dB of one another then it is considered that there is no air-bone gap.
audiogram4.png


Audiogram 5:
Audiometric assessment shows a severe to profound hearing loss.
This audiogram cannot be defined as sensorineural or mixed because there is insufficient information. This is because there were no responses to bone conduction.
We do know that this is not a conductive hearing loss because the definition of a conductive loss is that the bone conduction is within the normal range but the air conduction is out of the normal range.
audiogram5.png
Audiogram 6:
Mr B suffers from a profound hearing loss.
This is called a corner audiogram. It is possible these are tactile responses.
In this case bone conduction has not been attempted. The most likely explanation for this is that this is a repeat audiogram to check that the hearing loss is stable and previous testing has shown no response to bone conduction.
audiogram6.png


Audiogram 7:
Audiometry shows hearing is within normal limits to 1kHz with a steeply sloping, apparently sensorineural, moderate to severe loss, above this.
The words ‘apparently sensorineural’ are used because there is limited information to say this at this stage. This is because there was no response to bone conduction at 2kHz and 4kHz. The position of the symbol showing that there is no response has been placed at 70dBHTL. This shows that the maximum output of the audiometer was at this level.
When we talk about audiograms it is customary to describe them based on the results between 500 and 4kHz.
audiogram7.png
Audiogram 8:
Hearing test shows a moderate hearing loss in the low frequencies sloping upwards to a mild loss in the high frequencies, bilaterally. The hearing loss is conductive in nature in at least one ear. Further testing is required, however, masking was not attempted as P is only 4 years of age and had become inattentive.
Masking is often possible in children if you can maintain their attention span. Some children become confused with masking and cannot manage. In this case you could write something like ‘Masking attempted but unsuccessful’
A hearing loss that is purely conductive cannot be greater than a moderate loss or putting it another way, a maximum conductive loss is around 70dBHTL.
When the hearing levels from both ears are within 10dB of one another at a particular frequency then they are considered to be symmetrical.
audiogram8.png

Audiogram 9:
Audiogram shows hearing is within normal limits except at 3kHz and 4kHz which show a mild sensorineural loss in a ‘notch’ pattern, consistent with the effects of noise.
Audiometrists cannot make medical diagnoses so you can’t say ‘the hearing loss was caused by noise’ but you can say, ‘the hearing loss is consistent with the effects of noise’ as a ‘notch’ is unlikely to be caused by anything other than noise. You would also expect that the client’s history would show excessive noise exposure.
A Noise Induced Hearing Loss (NIHL) will often show a ‘notch’ pattern. After many years of noise exposure the notch will start to flatten out and the audiogram will be similar to that of presbycusis.
audiogram9.png
Audiogram 10:
Audiogram shows a mild-moderate high frequency hearing loss of a sensorineural nature.
Presbycusis is the name given to hearing loss caused by aging. The typical configuration or shape, is a sloping high frequency sensorineural hearing loss. This is also the most common pattern for all hearing loss. That is, most people who have a hearing impairment will have a high frequency loss. However, you CANNOT say ‘This hearing loss is caused by presbycusis’ because only a doctor can say that.
audiogram10.png


Audiogram 11:
Audiogram shows a bilateral mild-moderate hearing loss. It is conductive in nature in at least one ear. Further testing is required.
Conductive hearing loss is caused by many conditions of the outer and middle ear. The most common causes of conductive hearing loss are otitis media (in children) and otosclerosis (in adults). Conductive hearing loss shows an air-bone gap on the audiogram. You often see an effect called the Carhart’s notch. This is where the bone conduction is affected at 2kHz by the condition of the middle ear. If the client undergoes successful surgery, it is likely that the bone conduction at 2kHz will improve.
It is usual for a conductive hearing loss to affect the low frequencies more than the high frequencies.
This client requires masking, until you know how to do it yourself you would ask your supervisor to take over the testing
The audiogram may alert the clinician to problems in the testing procedure.
audiogram11.png


Audiogram 12:
If the earphones are causing collapsing canals the audiogram will show an air-bone gap in the high frequencies. It is unusual to have an air-bone gap in the high frequencies so you must always check for collapsing canals.
To correct this problem, place the earphones correctly or ask the client to hold the earphones against their ears without too much force. If you have access to E.A.R. insert earphones you could try using them.
audiogram12.png

Audiogram 13:
Incorrect placement of the earphones has the greatest effect in the high frequencies, especially at 6kHz. It is advisable to quickly recheck thresholds in the highs after repositioning the earphones. If the earphones are placed incorrectly the thresholds in the high frequencies will improve after repositioning the earphones.
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TOPIC QUESTIONS


You should be prepared to answer questions from clients, teachers and supervisors. If you do not know the answer of a reasonable question, write it down and do the research and learning to be able to answer it the next time it is asked of you. You should then check with your supervisor or teacher that you are able to answer the question.

What are you doing when you perform audiometry?
What is a subjective test?
What is an objective test?
Why do you need a quiet test environment?
How do you know a test environment is quiet enough?
How do you seat a client?
What is a hearing threshold?
How do you instruct the client to respond in a hearing test?
What might happen if you do not place earphones correctly?
When would you use insert earphones?
In what order do you test the frequencies?
What is the rule for testing mid-octave frequencies?
Which ear do you test with a bone conductor?
Why must you present the sounds in a hearing test randomly?
How do you treat clients experiencing tinnitus?
What are tactile responses?
Describe degree of hearing loss.
How is type of hearing loss described?
How is type of hearing loss shown on the audiogram?
How do you explain the results of a hearing assessment to clients?
What is 3FAHL and how do you derive it?
Why establish SRT?
What is the purpose of speech testing?
Why would you test speech at 3FAHL + 30?
Can you refer directly to an ENT?
What 4 components should a report include?
When would you ask the client to see someone else?