Factors which affect our ability to understand speech – Part 1

Why we all have difficulty hearing and understanding sounds, in particular speech, from time-to-time: Factors which affect our ability to understand speech – Part 1

Most people encounter difficult listening situations every day; situations when they can hear speech and/or noise but they can’t always decipher and understand what the sounds mean. There are many factors which challenge our ability to hear and understand speech. I will explain some of those factors in this post.

First, though, in a previous post I explained the anatomy of the ear and how we hear. For those readers who may not have seen that post, a quick review is warranted.

If you think a picture of the auditory or hearing system would be helpful while you read this post, simply, type, “anatomy/images of the ear” into your favourite browser and you will see many links that will provide you with pictures of the ear.

The ear per se is divided into three sections: the outer ear, the middle ear and the inner ear. The outer ear consists of the parts of the ear that you can examine visually and includes the ear canal and the ear drum.

Just beyond the ear drum is the middle ear which is a space about the size of a pea. The middle ear contains the three smallest bones in the human body, the malleus (hammer), incus (anvil) and stapes (stirrup). These bones together are called the ossicular chain which is attached to the ear drum at one end and the oval window at the other end. Also, the middle ear is connected to the back of the throat by the Eustacean tube.

The purpose of the middle ear is to make sure that sounds get from the outer ear to the inner ear accurately and to equalize the pressure in the environment around us with the pressure in the middle ear so the ossicular chain can vibrate as it should.

The inner ear (cochlea) is a snail-shell shaped, fluid-filled cavity in the temporal bone of the skull. It is filled with a special fluid and hundreds of thousands of tiny hair cells which change the vibrations from the middle ear into electrical impulses which are sent along the auditory nerve to the brain.

I consider the brain to be the fourth and a very important part of the auditory or hearing system. Without the brain you wouldn’t be able to understand what all the electrical impulses from the inner ear mean.

So, how do we hear? Sounds are conducted from the environment around us down our ear canals, causing the ear drums to vibrate. The movement of the ear drums cause the ossicular chains (in the middle ear) to vibrate against the oval windows which sit between the middle ear and the inner ear. Generally speaking, the movement of the ossicular chains helps to determine the power (loudness) of the sounds which are sent to the brain.

The vibrations of the oscciular chain are conducted into the inner ears and are changed into electrical impulses by hundreds of thousands of inner hair cells. The electrical impulses are sent along the auditory nerve to the auditory cortex in the brain. It is the brain’s responsibility to receive the electrical impulses and make them meaningful to us so that we hear and understand what is being said by the listener.

Simply put, the ear is the mechanism that sends the sounds to the brain. The brain is the mechanism that helps us decipher and understand what the sounds mean. I constantly marvel at how this system works to help us communicate with others!

Even with normal hearing there are obstacles which interfere with our ability to listen. We may hear sounds around us but we can’t always decipher what the sounds mean.

Some of the factors that may interfere with out listening include; but are not limited to:

1. The loudness of the sounds. Is the speaker whispering or is s/he talking over the extraneous environmental sounds?

2. The distance the sounds are made from the ears. Is the listener close to the speaker making it easy to hear and interpret the message or is the listener a distance from the speaker so that the listener is aware that the speaker is saying something, but can’t make out what is being said? Is the speaker talking next to the listener or is the speaker calling from another room or floor in a house?

3. The extraneous noise that is between the sound source and the ears. Are the speaker and listener in a quiet cozy corner with a little bit of extra noise or are the speaker and the listener in a crowded, noisy place making it hard to hear and interpret what the speaker is saying?

4. How clearly the speaker is talking. Does the speaker speak softly and mumble or does s/he enunciate words so they are easier to hear and interpret?

5. How interested the listener is in what the speaker is staying. Is the speaker entertaining and telling the listener something new or is the speaker telling a boring story that the listener has heard many times before?

6.How tired the listener is and able to hear and decipher what is being said. Is the listener interested and alert to conversation even in a noisy environment or is the listen tired and thinking about other things while trying to listen to the speaker?

7. And, the condition of the “listening environment”. Are there wall hangings on the walls and carpets on the floor or, is the room decorated with tiles and bricks which reflect the sound waves and make it more difficult to hear?

Hearing and understanding become more and more difficult as the listening conditions become more challenging.

Now, add a hearing loss to the mix and it is no wonder that, in many circumstances, people with hearing loss have trouble hearing and subsequently, understanding. Often they will tell you that they can hear something but they can’t understand what they are hearing.

But, that’s a topic to be addressed in future posts. Stay tuned.

If you have not already done so, you might find it helpful to read my previous posts. To a certain extent I have designed my posts sequentially, although the information in each post does “stand alone” and can help you understand more about hearing and hearing loss. Enjoy!

Glen Sutherland, MCISc
Audiologist

Please note that the information in this blog is presented for the purpose of providing information and should not be used for medical diagnosis or treatment nor should it be used in place of medical advice from your doctor or hearing health care professional.

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