Deafness is hearing loss of any degree – from a slight loss to a total inability to hear sound. There are two primary types of deafness: Sensorineural and Conductive. There is also mixed which is when someone has both a sensorineural and a conductive hearing loss.
How do we diagnose deafness? To diagnose deafness, hearing tests have to be performed. When hearing tests are performed properly, individuals are placed in a soundproof room and an audiologist sits outside the room. The individual wears headsets and sounds are transmitted from a computer to the head sets. The tests are ran using tuning fork sounds at varying pitches and then also varying decibels. Words are also said across the head sets in two formats: masked and unmasked. Masking the words when they are said or placing a hand over the mouth as the words are said impacts the sound waves ability to travel. So hearing words are tested in both formats to test the individual's ability to detect the words properly. The individual being tested then uses a button to respond to the tuning fork sounds and repeats the words back for any spoken tests. The audiologist then records the results on an audiogram as seen below.
This is an audiogram. An audiogram is created when a hearing exam is completed. The pitch is the frequency of the sound and it is on the x-axis. The hearing level or volume is recorded in decibels. To give you a frame of reference, spoken language syllables fall between 20 - 65 decibels typically at varying frequencies ('j' and 'z' are low frequency sounds and 'th' and 's' are high frequency sounds). Looking at the far right, you can see the normal range for hearing and then the severity of the hearing loss as it moves down. The louder a sound needs to be to be heard the more profound the hearing loss. In this particular image, the individual has a mild to moderate loss because they are borderline for three frequencies.
Here is another audiogram. This one shows you pictures of common items and where they fall in terms of both frequency and decibels. Take notice to spoken language as this is the most important in terms of communication.
The location of the type of hearing loss is indicated in this image. Conductive hearing losses occur within the outer to middle ear whereas Sensorineural hearing losses occur within the inner ear or brain.
Conduction Deafness is the interference with the conduction of sound vibrations through the inner ear. This means there is a problem with the outer or middle ear. The causes of conduction deafness can be wax, bone malformation, growths, ruptured eardrums, or otitis media. For some causes such as wax formation, or ear infections can lead to a temporary impairment which means once the problem is eradicated the person's hearing returns to normal. Other causes such as bone malformations, growths, and ruptured eardrums are more permanent. Bone malformations can occur during development in the womb, whereas growths could happen at any one point in someones life for no reason. Ruptured eardrums are usually the result of a loud noise or possibly something be forced into the ear. Bone malformations cause the bones to not form properly and therefore sound vibrations can't be passed into the inner ear correctly. This is permanent condition. Growths may be permanent or they may be something that can be fixed through surgery. However, sometimes the surgery to remove the growth results in bone damage and the loss is then permanent. Ruptured eardrums will heal, but scar tissue will replace the damaged area resulting in an ear drum with less flexibility so although hearing is typically more improved from when the rupture was present, the scarring will result in permanent damage.
So what does conduction deafness sound like? It depends upon the individual and the severity of the loss, but in general a conduction deafness results in sounds being heard at a much lower volume or decibel than they are in reality. Think about it this way... you're riding in a car and someone turns the stereo down, its not as loud as it was moments ago. To someone with a conductive hearing loss that original volume would have sounded like the volume once it was turned down. Everything is not as loud as it really is. Sounds are muffled.
Here is an audiogram of a conductive hearing loss. The individual's results are shown by the "x" marks and the solid blue line. That is the baseline for them hearing those frequencies. So as long as the frequency is at that loudness or louder they can detect and hear it.
The following video provides an example of a conductive hearing loss.
Sensorineural Deafness is the degeneration or damage to the receptor cells in the organ of Corti, to the cochlear nerve, or the neurons of the auditory cortex. It is caused by genetics, exposure to excessively loud sounds, old age, a virus, brain damage, and underdevelopment while in the womb. If the loss is genetics based (there are many forms) it is passed on from one generation to the next. Exposure to loud sounds, like listening to your music with your earbuds and the person sitting next to you can understand the words... ITS TOO LOUD!!! Being around loud sounds without ear protection such as lawn mowing, concerts, construction jobs, etc. These sounds wear down the nerves in the inner ear and they don't work properly. Getting old - ah, a fact of life, and as one ages the nerves in the ears are older and begin to degenerate or wear down, and hearing loss results. A virus - yes, a virus, such as meningitis can cause nerve damage in the ears. Brain damage... makes sense right? If the auditory nerve or temporal lobe are damaged in the brain then hearing won't be detected. Finally, there is underdevelopment in the womb. Simply put, the inner ear doesn't form properly or maybe at all. A sensorineural loss is permanent - it is NERVE damage.
Here is an audiogram of a sensorineural hearing loss. The individual's results are shown by the "x" marks and the solid blue line. That is the baseline for them hearing those frequencies. So as long as the frequency is at that loudness or louder they can detect and hear it. Notice the high frequencies are most affected. This is MOST common. Why? The high frequency nerve fibers (hairs) are at the entrance of the cochlea and low frequency nerve fibers are further up in the cochlea. High frequency nerve fibers are also more sensitive and fragile than low frequency fibers are. Therefore they are damaged more often.
So what does a sensorineural hearing loss sound like? This is a little more challenging to describe than a conduction loss because sensorineural hearing losses are nerve related. So it doesn't always mean "make it louder and they'll hear it!" Sometimes if the nerve for a frequency is not present or is degenerated to the point it doesn't work, it doesn't matter how loud you make a sound they will never perceive it. Other times, talking more loudly or turning up a volume will help because it moves to a decibel in which the nerve will pick up the sensation. Sensorineural losses, especially those that are high-pitched affect spoken language more than anything. For example: Sally says: "Joe has a six pack of soda for us to share this afternoon." Someone with normal hearing hears exactly that. A person with a moderate high-frequency loss may hear "Joe ha a i pac o oda or u to are i aternoon." Yes, I purposely misspelled the words because the missing letters fall in the high frequency loss range. Can you imagine? So the brain now has to compensate and either respond by saying "what?", "repeat?", etc. or the brain fills in what's missing and tries to make sense of it - in which case it may be right or completely wrong. People with this type of loss are also affected by sound barriers - talking with hands in front of the mouth, facing a window or wall while talking, talking in noisy environments. These all impact how the person hears what is happening or being said to them.
The following video will demonstrate a high frequency hearing loss.
How do we treat hearing loss? Hearing loss is treated by fitting the person with a hearing aid (or two of them). There are different kinds of hearing aids (see image below) and age and type of hearing loss are sometimes used to factor in which kind of hearing aid a person receives. Hearing aids are great tools for someone with a conductive hearing loss because hearing aids amplify the sounds - they make them louder! Hearing aids aren't as beneficial to someone with a sensorineural loss because sometimes the nerve can't perceive the sound regardless of how loud it is and if the amplification has to be so loud for them to hear certain frequencies other frequencies will be overbearingly loud. So hearing aids are beneficial to both but they really help a person with a conductive loss! However, technology is continually improving and so hearing aids may continue to be better adapted to help with sensorineural losses. If the person has a profound loss or is completely deaf then a cochlear implant (see image below) is typically used, which requires surgery. Additionally, there are speech therapies to help individuals learn to pronounce sounds they can't hear and also learn sign language if needed.
Closure: How is a conductive hearing loss different from a sensorineural hearing loss? Submit your answer on Socrative. (If it's not open - remind your teacher!)