A Map of your Hearing

A Map of your Hearing

Compass on a city map

An audiogram is a visual representation of one’s hearing ability. You can think of it as a map that helps us understand someone’s hearing experience. In order to understand how this map works, we need to review how our auditory (hearing) system functions.

How we Hear – Quick Overview

When an object moves, it creates a vibration in the air that travels outwards in all directions until it reaches an ear where the sound can be heard. Most people are not aware that there are two pathways/mechanisms at work that contribute to how people hear: air conduction and bone conduction. Most people are familiar with air conduction hearing in which sound travels naturally down your ear canal to the middle ear onto the inner ear and then up to the brain.

The inner ear contains the main hearing organ known as a cochlea. Both cochleae are encased within the temporal bone of the skull. Bone is a very good conductor so when the skull vibrates, so do both cochleae. This leads us to the second mechanism of hearing through bone conduction where vibrations of the skull get directly transferred to the cochlea.

Here, the mechanical vibrations (sounds) are converted into electrical impulses to be sent up to the brain for processing. Bone conduction hearing bypasses the outer and middle ear and gets straight to business in the inner ear.

The Audiogram

An audiogram is a graphical representation of an individual’s hearing levels. After a hearing test is conducted in which both the air conduction and bone conduction pathways are tested, the results are mapped onto the audiogram. To learn more about how hearing is tested click here.

Let’s take a look at the audiogram now.

Along the horizontal axis of the audiogram you can see the range of frequencies that are typically tested. Low frequencies can be seen on the left side (bass) moving to high frequencies on the right (treble), similar to a piano.

The vertical axis represents the presentation level (volume) of the tones by the audiologist from very quiet at the top to very loud at the bottom. The presentation level of the tones is in dB HL (decibels, hearing level).

Some audiograms also have a banana-shaped shaded area in the middle of the graph. This is known as the speech banana. It encompasses all of the speech sounds that we hear, at what frequency we hear them and how loud they are in every speech.

Having the speech banana on an audiogram can be a useful tool as the audiologist can visually see which speech sounds are audible and which are not based on how an individual’s hearing thresholds are mapped out on the speech banana portion of the audiogram.

After testing is complete the results from the hearing test will be graphed onto the audiogram using several different symbols. These symbols indicate hearing thresholds. A threshold is the quietest sound that an individual can hear at a given frequency.

Individuals with normal hearing have very low thresholds between 0-20dB*. So, when the symbols appear at the top of the graph it indicates that the volume did not need to be very loud for the patient to hear it. As the symbols migrate towards the bottom of the graph, it shows that the tones needed to be presented at louder volumes before the patient indicated that they heard something.

The location of the symbols on the graph will depict the degree of hearing loss an individual may have. Above 20dB is within normal range, between 20-40dB is a mild hearing loss, 40 – 55dB is moderate, 55-70dB is moderately severe, 70-90dB is severe and beyond 90dB represents a profound hearing loss*.

The Symbols

Audiologists use ‘X’s to represent left ear thresholds and ‘O’s to represent the right ear thresholds. The ‘X’ and ‘O’ represent the results from air conduction testing. Recall that if a hearing loss is identified – the ‘X’s and ‘O’s are lower down on the audiogram – bone conduction testing needs to be completed to determine where the problem is occurring (middle ear or inner ear).

Patient responses by bone conduction are denoted by ‘>’ for the left ear and ‘<’ for the right. In addition to the different symbols, audiologists may use the colour blue to indicate left ear responses and red for the right ear responses.

In some cases, an additional noise may be presented to one ear during bone conduction testing. Since the skull is such a good conductor, the vibrations of the oscillator will stimulate BOTH cochlea (left and right).

Therefore, in order to determine which cochlea is responding the additional noise allows us to keep the non-test ear “busy” to ensure it isn’t “helping out” the ear currently being tested. This is called masking and it allows the audiologist to isolate each cochlea separately. The symbols to denote these masked responses are ‘]’ for the left ear and ‘[‘ for the right.

Interpreting the Map

Now that you understand how the audiogram is created and how to read it, it is time to interpret it to get an understanding of the patient’s hearing experience.

If the patient is identified with a hearing loss, depending on the degree of loss, the audiologist can understand how and why they may be struggling with their hearing. The audiologist should always explain the results in detail with the patient and this is where having the visual representation of the audiogram comes in handy!

The audiologist should also explain how the hearing loss can affect the patient’s day-to-day interactions with the world. Depending on the patient’s difficulties and the level of hearing loss, treatment in the form of hearing aids may be recommended.

Now you should be able to read your audiogram!

Remember, if you feel you are not hearing as well, struggling to follow conversations, or have difficulty hearing the TV you should contact your local audiologist for help. Getting a hearing test is the first step towards better hearing.

*there are some minor discrepancies (~5dB) across professionals in regards to the exact dB HL levels that describe each hearing loss degree.

 

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