Audiologists are skilled at using a range of techniques and specialised equipment to assess your hearing.
Before performing a hearing test, an Audiologist will first examine the health of your ear canal and the tympanic membrane with an instrument called an otoscope. This inspection can provide a lot of information about what’s happening within the middle ear. It also identifies if there are any visible problems that may influence the results of hearing tests, such as a perforation in the tympanic membrane or compacted build up of cerumen (ear wax).
How is Hearing Tested?
Air Conduction Testing
Pure tone audiometry is the simplest way to test hearing. This involves listening to a range of different pitched beeps (called pure tones) and indicating when you can hear them, generally by pressing a button.
The loudness of each tone is reduced until you can just hear the tone. The softest sounds you can hear are known as your hearing thresholds, and these are marked on a graph called an audiogram.
When hearing is measured with pure tones presented through headphones, this measurement is called air conduction. The sounds go via the air, down the ear canal, through the middle ear, and to the very delicate organ of hearing in the inner ear— the cochlea.
Bone Conduction Testing
The sensitivity of the cochlea can also be tested by bone conduction. This involves placing a small vibrator on the mastoid bone behind the ear and again measuring the softest sounds that can be heard. Sounds presented this way travel through the bones of the skull to the cochlea and hearing nerves, bypassing the middle ear.
The air conduction and bone conduction hearing levels on the audiogram can tell us a lot about where a hearing problem is originating. For example, if bone conduction tests indicate less hearing loss than a test through headphones, results would indicate that at least part of the hearing loss can be attributed to conductive hearing loss. Reasons could include fluid in the middle ear, excessive wax, a perforated tympanic membrane, or that the bones of the middle ear are not functioning normally.
The ability to interpret speech is a function of the ability to detect and understand the sounds of speech. The range of audible sounds, not just the degree of hearing loss, varies considerably from person to person.
Unfortunately, when hearing is damaged it is usually not just the volume of sound heard that is lost, often the quality of the sound is also distorted.
Speech tests are used to determine how clearly someone can understand speech, when visible cues such as lip-reading are removed. They usually involve using common lists of words played (or spoken) at a constant volume that is appropriate to the client’s hearing loss.
The client responds by identifying the word that was spoken and correct and incorrect answers are tallied.
People with hearing loss commonly have the greatest difficulty understanding speech in the presence of background noise, it makes sense that speech discrimination tests are also performed with the addition of a “noise” stimulus.
This is often a ‘speech babble’ played at different volumes relative to the loudness of the speech (words or phrases). The client responds by guessing the word or phrase that was spoken in the presence of background noise. Again, the results are tallied.
A tympanometer simultaneously changes and measures the pressure in the middle ear. An acoustic stimulus is supplied at varying levels of pressure. The physician is then able to assess, among other things, the functioning of the eardrum, and determine if there is fluid present in the middle ear. It is not a hearing test in itself, but is used in conjunction with other tests to assess ear health.
Reading Your Audiogram
An audiogram is a chart a hearing test is marked on. The degree of hearing loss is measured in dB for defined key frequencies. The frequency is measured in Hertz (Hz). Curves displayed in decibels (dB) generally describe the individual hearing threshold of a person compared to the normal hearing average, which lies around 0 dB. Due to individual differences, all thresholds up to 20 dB hearing loss are considered normal.
The vertical lines represent the test frequencies, arranged from low pitched on the left to high pitched on the right. The horizontal lines represent loudness, from very soft at the top to very loud at the bottom.
Symbols are placed on the audiogram that show the person’s air conduction and bone conduction thresholds for each of the key frequencies. The audiogram shows the softest level at which a sound is perceived. This is also referred to as the hearing threshold. Different symbols are used to distinguish between air- and bone conduction measurements, as well as which ear the measurement refers to.
To read and understand an audiogram, look at the loudness level and frequencies of different speech sounds presented in the audiograms above. Because of the shape of this speech area, it is also referred to as a “speech-banana”. Vowels are low frequency sounds with a higher volume than consonants, which are soft high frequency sounds. The vowels carry the loudness impression of speech whereas the consonants carry the meaning, e.g. house or mouse.