Hearing experiments

Introduction to deafness

Deafness - either total or partial - is a significant health issue today. A major source of this problem is due to loud sound. The likelihood of going deaf due to loud sound is increasing because of occupational and recreational sources of loud sound.

Now you may think deafness isn't that problematic. One of the major problems with deafness is social isolation. You stop attending parties or going out because understanding people, especially in even moderately noisy environments, becomes a problem. Something you have to strain at. And that's demanding – it makes you tired even after only a few minutes. There are also all the other problems – you mishear what the service attendant says you owe, and find you've underpaid – oh the embarrassment of it. Or even worse, when you think someone said something rather different from what they actually did and you respond in an inappropriate way...

Let me remind you of the statement of Helen Keller, who was both deaf and blind:

"Blindness separates people from things; deafness separates people from people."

So look after your hearing – it can only get worse from birth.

We measure sensitivity with tones

Given the wide variety of sounds that we encounter in life, how can we measure hearing losses in a meaningful way? We can take advantage of the fact that the inner ear (also known as the cochlea), which converts sound from pressure waves into biological energy, is organized in a way that each part of the length of the cochlear responds best to a different frequency of sound (think of this as being analogous to pitch – low frequencies are ones we hear as bass and high frequencies are ones we hear as treble).

Each frequency of sound we hear, at low sound levels, best activates one particular place in the cochlea, and this organization is maintained in all the structures of the brain that receive input from the inner ear, all the way up to the primary auditory cortex.

This means we can define hearing losses by measuring hearing sensitivity (thresholds) at each of a number of different frequencies, choosing frequencies that cover the range of frequencies we can hear (well there's no point trying to measure our sensitivity to very high frequencies that bats can hear, but we can't; or very low frequencies that elephants or moles can hear, but we can't!).

A plot of threshold at each frequency is called an audiogram. The following simulation is an online version of measuring the audiogram. Note that you should NOT treat this as being a definitive test of your hearing sensitivity. The room you're in may be noisy; the earphone or headphones you're using are not calibrated; etc. Use this merely to get a feel for how to measure hearing.

You could also use it to mimic some hearing loss conditions in the following way: measure your hearing as per the instructions. Then put a hearing protector in one ear canal and repeat the measurement (and no, don't put anything sharp or anything else in your ear canal!). This allows you to mimic the effect of having wax in your ear canal, or a cold or flu, when mucous may block your middle ear.

During the simulation your hearing thresholds will be plotted in an audiogram. Take note of these values (or print them using the provided links) so you can compare your hearing to that of different populations in the following experiments.

What is an audiogram?

An audiogram measured by an audiologist using an audiometer converts measured thresholds from absolute sound pressure level to a hearing threshold level relative to the normative population, thereby allowing direct reading of the loss in hearing sensitivity at each frequency relative to the normal population. It's like saying we're not going to measure the height of everyone in the class in metres; rather we're going to grab the person who looks like they are of average height and express everyone else's height in terms of whether they are shorter or taller than that person.

Audiometers have been designed so that they already have stored in them the average hearing level at each test frequency, measured from a very large number of people with good hearing. That means the value that the audiometer reads out for your hearing is how much better or worse your hearing at a test frequency is, compared to the average normal hearing at that frequency (i.e., in the example above, how much taller or shorter you are compared to the average height in the class).

Measure your hearing sensitivity

Below we have embedded an excellent website (https://hearingtest.online/) that allows anyone to test their hearing thresholds. Go through the page and when you have your thresholds, come back to this table to fill them out (make sure to click on the button to save your thresholds). This will allow you to compare your hearing to the aging and loud sounds data.

Speech perception tests allow examination of the functional consequences of hearing loss

Tests of your ability to understand speech (speech discrimination tests) are useful because they examine a practical and functional consequence of a hearing loss. They may also help identify retrocochlear lesions (damage to sites beyond the cochlea, or inner ear).

Simple speech discrimination tests use a standard word set (monsyllabic or disyllabic words generally). Each word set is presented at each of a number of different levels. The subject's task is to identify as many of the words as possible. The results are plotted as the percentage correctly identified (the Word Discrimination Score) versus the intensity of the stimuli.

More complex speech discrimination tests use more complex stimuli like words or even sentences. An issue with the latter is to ensure that the test battery is appropriate for the patient – i.e., a child may not respond to a word or sentence not because they didn't hear it but because they don't have the vocabulary to comprehend that stimulus. This may also be the case with people who have as a second language the language used in the speech test.

In addition to identifying functional consequences of hearing losses, speech discrimination tests, in combination with audiogram data, can help identify the presence of retro-cochlear lesions.

Here is an online speech discrimination test from Peter Blamey and Elaine Saunders who run a hearing aid company. Peter has kindly given permission for us to provide you access to this test, but asks only that you do the test in a serious way – as he said "If the students don't wish to use their own names to preserve anonymity that's OK, but please ask them to do the test in the normal way so that we do not end up with a lot of spurious data". At the end of the test you will get a set of results on your own hearing, broken down by type of speech feature. You can interpret that result by going lower down on the results page to read what the speech feature means.