If we could see hearing impairment, what would it look like?
Here’s one way to think of it. Lets begin our analogy with an image:
This is how a neurotypical person would see the image. The colours are vibrant, edges are clear and objects can easily be picked out. Now imagine if we saw this picture in the same way people generally think hearing impairment works – where everything is simply less intense.
It obviously doesn’t look like our original photo, but its still easy to parse out most objects. The only aspects that are particularly difficult are those areas that were not very intense to begin with, like the shadowed trees in the background (compare this to whispers, which are generally difficult to pick up for even normal hearers). However, this image does not represent a proper visual analog to hearing impairment.
Most hearing impairments are sensorineural, which generally means they are caused by an absence, damage, or dysfunction of the hair cells of our auditory organ, the cochlea. Normally, this pea sized organ is coiled up in our inner ear, but for illustrative purposes if we uncoil it, we can see that it has areas which respond best to different frequencies of sound. Hair cells exist throughout the cochlea and fire to sounds that correspond to their place on the cochlea. When disfunction occurs, it does not equate directly to the perception illustrated above where intensity is simply diminished; its a little more complicated than that.
To use a visual analogy, think of your TV screen or computer monitor. These machines display images using tiny little points of light called pixels. If you have more pixels per unit of surface area, you have a clearer image with a higher resolution. In your cochlea, you can think of your hair cells as pixels too, and your brain as the person watching the screen. If hair cells become damaged or dysfunctional, we have a reduced hearing resolution and our brain has less information to work with. To see this, we can simply reduce the resolution of an image. The intensities of the various colours remain the same, but the image is less clear and objects are harder to pick out, just as it can be harder for individuals with hearing impairments to pick out words from noise, even when the volume is increased.
Of course we know there is way more to light than just intensity and resolution. Just like sound, light is made up of a range of perceptible wavelengths. It is crucial to understand that the perception of various frequencies are generally not all equally affected in those with hearing impairments.
In this image the low frequencies (red light) have been greatly reduced in intensity. Though we lose some information about the scene (colour, shading and texture of the canoe), its still relatively easy to identify and separate objects seen. It would seem that the low frequencies are relatively unimportant for pulling out information from this image, just as low frequency hearing impairments generally have a relatively lesser impact on speech perception than higher frequencies.
This image represents an individual with a sloping high frequency hearing impairment, where short wavelengths (green) are reduced and very short wavelengths (blue) are reduced further. Certain aspects of this image are much more difficult to perceive. The trees are difficult to parse from one another, just as the separation between sky and mountain or water to ground are harder to perceive. However, this still doesn’t quite capture the whole experience of hearing impairment either. Instead, we need to factor in our reduced “hearing resolution” which we discussed earlier.
In this image, it becomes very difficult to perceive various aspects of this scene due to both the resolution and the colour balance. However, we’ve now seen this image several times, so lets try something new.
How many cars are in this image? What does the green sign say? Do you see the streetlights? The mountain? The pylons?
Here is the unaltered image. A lot of information got left out in our hearing impairment simulation!
I hope this helps to illustrate hearing impairment, though it is important to recognize that this is far from a perfect representation. In reality, everyone’s unique hearing abilities are different and other aspects of hearing loss that don’t have good visual analogues exist as well.
(This post was originally published in October, 2015)