Glossary
The terms in this glossary provide more than just a definition, they explain more about what people with hearing loss should know about each term. More terms will be added if it proves useful.
Terms
Audiogram
An audiogram is used to record the results of a hearing test. It includes a graph for each ear showing the quietest pure tone sounds you can hear at various frequencies, typically up to 8 KHz (thousand cycles per second). The graph includes measurements in decibels (dB) for sound waves arriving at your ear drums typically plotted as O for right and X for left, and vibrations induced into your mastoid bone behind the ear typically plotted as < for right and > for left. The graph dominates the audiogram, which also typically records the results of other tests that indicate how well various parts of your "hearing system" are working. For example, it may include:
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Your ability to recognize words.
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Your ability to understand words in context.
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Your ability to hear in noisy situations.
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The flexibility and response of your eardrum.
Auditory Nerve
The auditory nerve is a bundle of nerve fibers that carries hearing information between the cochlea the brain.
Usually, hearing loss that is called "sensorineural" or "nerve deafness" is actually caused by problems with the cochlea, instead of the actual auditory nerve, but a very small percentage of hearing loss is caused by problems with the nerve, itself. The auditory nerve and the vestibular nerve, which carries balance information from the semicircular canals to the brain, join together as they pass through the bony canals of your skull. Also passing through the same bony canals of your skull is the 7th cranial nerve, or the facial nerve, which supports facial expression and sensation. It's interesting to note that while many of the nerve fibers in this bundle do carry the sound signal to the brain, most (some estimates are as much as 2 thirds) of the nerve fibers actually carry information BACK to the cochlea from the brain. The cochlea can then use this information to suppress sound you are not interested in ... like background noise. This explains why hearing aids (which amplify sounds) can help you hear better, but they do not completely correct a hearing loss.
Bluetooth
Bluetooth (standard) is a wireless protocol that allowed two objects to communicate between each other. Originally, it was used to communicate between computers and peripheral devices, but later allowed streaming audio between audio sources and hearing aids. At first, streaming with Bluetooth required an accessory with a compatible Bluetooth receiver in it that acted as an intermediary device and used a neckloop to stream to the hearing aids' telecoils. That was necessary because of three reasons:
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Hearing aids didn't have a Bluetooth receiver
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Audio streaming required more energy than hearing aids batteries have
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The latency (delay) of the received audio was too great to allow speech reading.
Soon, Bluetooth Low Energy (BLE) was developed and adopted by Apple, ReSound GN, and Cochlear Corporation. Apple called it Made For iPhone (MFi), and it was the first to allow streaming from Apple smartphones to compatible hearing devices. MFi can not stream from standard Bluetooth sources. A limited number of Android smartphones models quickly included the MFi protocol. Later, an "Android Streaming for Hearing Aids" (ASHA) protocol was created using BLE to allow most Android phones to stream directly to hearing devices, and was able to also stream from standard Bluetooth sources.
Today (2024) Bluetooth audio sources and receivers like TVs, and computers currently use standard Bluetooth. But that may be changing.
Newer versions of BLE starting at version 5.2 are being developed and deployed that may make relatively inexpensive transmitters and receivers widely available in a few years. It will take time, because TVs, computers and venues like movie theaters, live theatres, churches, etc will need to install the transmitters plus hearing devices (hearing aid, CI, headphone and earbud manufactures will need to include the receivers in new devices. These new versions provide additional and revolutionary features like broadcast (Auracast), audio sharing, multi-language streaming, and further reductions in energy requirements for receivers. You can see more information about the future of BLE at www.bluetooth.com.
Cochlea
The cochlea is small (about the size of a baby lima bean) and snail shaped object in each of your mastoid bones behind each ear. It's filled with fluid and has about 15,000 hair cells (not really hair). The hair cells are arranged tonotopically (in order by frequency sensitivity) from the lowest frequencies near the apex of the cochlea to the highest frequencies at the larger end of the cochlea. At the base of each hair cell is a nerve cell that's the beginning of the auditory nerve. The ear drum vibrates when sound waves enter your ear canal. Three small bones attached to the back of the ear drum mechanically transmit and amplify the vibrations to the cochlea. That sets up waves in the fluid of the cochlea that stimulate some of the hair cells to send nerve signals up the auditory nerve to the brain, where they are perceived as sound. About half of the hair cells can send nerve signals representing sound at their assigned frequency to the brain. The other half can receive signals from the brain to adjust cochlear features like the membrane-like shelf over the hair cells to increase or decrease the sensitivity of various frequencies to improve hearing in noise.
Conductive Loss
If a hearing loss is caused by problems with the ear "conducting" the vibrations to the cochlea, then it is called a conductive loss. The problem may be with the ear drum or with the ossicles (three tiny bones). Conductive losses aren't the most common types of hearing loss. Nearly 80-90% of hearing loss is caused by a sensorineural loss, where the problem is with the cochlea or the auditory nerve Some forms of hearing loss are caused by problems with these bones. When the hearing loss is caused by these bones, it's referred to as a conductive loss A conductive loss is often a flat loss, affecting all frequencies. Hearing aids can be especially effective in helping someone with a conductive loss hear better. Many times a conductive loss can be fixed or at least improved with surgery.
Hair Cells
Hair cells in the cochlea are moved by the vibrations of the fluid in the cochlea caused by sound waves. The cells at the base of the hair cells convert their motion into electrical signals to be sent up the acoustic nerve to be interpreted by the brain as sound. Actually, the hair cells are not really hair; but the behave somewhat like hair might. Hair cells are also required for the cochlea to react to the brain's instructions based on the timing and volume differences that come from bilateral hearing. Those instructions are important, because they allow the cochlea to suppress noise somewhat so the brain can perceive speech better.
Damage to hair cells (or the lack of them) is one of the major causes of hearing loss. Hair cells can be damaged mainly by exposure to loud sounds, or ototoxic drugs. Research is underway with a goal of being able to regenerate hair cells, but progress in humans can't be counted on soon. Some other animals can, in fact, do this, but humans cannot, yet.
Different hair cells respond to different frequencies and give us our amazing ability to perceive different frequencies of sound correctly.
Loop
Or more accurately, "audio loop" is a source of a variable electromagnetic field representing an audio signal. An audio loop consists of an amplifier with an input of an audio signal ... perhaps a micophone or an audio from any audio source. Instead of speakers, the output of the audio loop of wire that creates the electromagnetic field that telecoils in the field will induce a comparable electronic signal representing the same sound. Audio loops may be installed around a room or a larger area like an auditorium, a church sanctuary, or a live theater. Some movie theaters are "looped", but most use FM or Infrared transmitters and personal receivers, because installing a large audio loop in a 16 or 20 theater multiplex can get expensive. Some loops are personal "neckloops" that are patched to any headphone jack or 3.5 mm audio output jack. A neckloop user can "stream" the audio from their TV, stereo, computer to their hearing aids, cochlear implant or a loop receiver. Venues that have installed loops allow anyone with telecoils in their hearing device to hear the program. People without telecoils can use a personal loop receiver with headphones.
Any individual in the audio loop's field that has hearing aids or cochlear implants with active telecoils will hear the broadcast signal. They can sit anywhere in the venue covered by the field. If their hearing device allows them to turn off its microphones, they will hear ONLY the broadcast signal and not nearby noise.
Loop America lets you search for installed loops near you. The LoopFinder app available for Apple iOS devices also can locate looped facilities. Google Search has information available about individual venues with installed audio loops.
Ossicles
Three tiny bones (the smallest bones in the body) amplify the vibrations representing sound from the ear drum and transmit it across the Eustachian tube (a cavity that opens into the throat) to the cochlea. These bones are formally named the "malleus", the "incus", and the "stapes", but they are more commonly known as the "hammer", the "anvil" and the "stirrup". If these bones are damaged, or calcified, they can result in a conductive hearing loss, because they are unable to effectively send the vibrations of the ear drum to the cochlea.
Patterns by Loss
When loss is measured on an audiogram, the amount of loss in Decibels (dB) is plotted by frequency and shows how loud a sound for various frequencies need to be for you to hear them. It's very important to note that the loss is not plotted linearly, but logarythmetically ... meaning a 50% drop in the line indicates a much more significant loss than 50% normally implies. The pattern of the graph is often a slope, either to the right (ski-slope) or left (reverse ski slope), but sometimes with a loss indicated in the middle or at the upper and lower ends of the frequencies (cookie bite). Those common patterns typically occur for a sensorineural loss. The pattern most common for a conductive loss is less curved with the line on an audiogram appearing more flat or straight across the chart.
Sensorineural Loss
If a hearing loss is caused by problems with the inner ear, then it is called a sensorineural loss. The problem may be with the cochlea or with the auditory nerve. Sensorineural losses are, by far, the most common types of hearing loss. The second most common type of loss is a conductive loss. With a sensorineural loss, the amount of loss usually varies with the frequency of the sound, so your audiogram will not be flat, it will slope or dip at various frequencies. The three most common patterns by frequency seen in sensorineural losses are:
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ski slope (about 90% are this type)
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reverse ski slope (rare)
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cookie bite (rare)
If you hear "pretty well" but have trouble understanding speech (sounds like people are mumbling) or if you don't hear well in noise, then a sensorineural loss is the most likely cause. Early hearing aids weren't very effective at helping sensorineural losses, but newer aids are very capable of amplifying frequencies you don't hear well without over amplifiying frequencies you do hear well. Sensorineural losses can sometimes (rarely, actually) be helped by drugs, but in most cases a hearing aid is the most effective way to hear better.
Telecoil
A telecoil (AKA T-Coil or T-Switch) is a tiny coil of wire around a core that will induce an electric current in the coil when it's in the presence of a changing magnetic field. Telecoils are available as an input option in many hearing aids and cochlear implants. Originally designed in the 1950's, telecoils allowed telephone users to hold those old fashioned phones up to their hearing aid, and the telecoil would "hear" the electromagnetic signals emitted by the speaker in the phone's earpiece. The telecoil would induce an electrical signal into the hearing aid's amplifier, and the user would hear the audio from the phone more clearly. Users could switch between hearing the aid's microphones, the telecoil or both.
Later, audio loops were developed that allowed a room or auditorium to be encircled with a loop of wire driven by an amplifier. A microphone to the amplifier could send its audio signal through the loop and a variable electromagnetic field representing the audio was created throughout the area. That broadcast the audio to anyone the loop with hearing aids or cochlear implants with a telecoil. Telecoils were the first assistive listening solutions that could broadcast to multiple people needing to hear better. Later still, personal FM transmitter send audio by radio to personal receivers, and people with telecoil equipped hearing devices could use a neckloop instead of headphones to hear the broadcast audio. Later still, Bluetooth could stream to compatible hearing devices, but initially could only support pairing between a single transmitter and a single user.
A newer version of Bluetooth Low Energy is expected in the future, which provide a feature called Auracast (broadcast capability) and other benefits like audio sharing, and multiple language support, but as of 2024, it's expected to be years before venues install compatible transmitters and end user by compatible receivers (hearing aids, cochlear implants, headphones and earbuds). Loops and telecoils are still a huge benefit, and will remain so, for decades.
It is expensive to install loop systems in auditorium sized areas. As a result, progress has been slow. Despite that, there are looped facilities around the US and in some other countries. Typically, these are churches, live theatres, and senior living venues with the ability to pay for a loop installation. You can find looped facilities near you HERE, or using an iPhone app called LoopFinder.
Many venues are not looped, but if they loan you an assistive listening receiver you can plug in a neckloop and hear via your telecoils. Better movie chains do have both headphones and neckloops, but you have to ask for the neckloop, if you want that instead of a headphone. You can also bring your own neckloop (about $50) if you have one. Neckloops can be a great option to hear in venues that offer an assistive listening receiver, if you don't have a remote microphone that patches to their receiver.
There are some limitations of telecoils that may make alternative assistive technology a better for some situations.
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Electromagnetic Interference (EMI) can be present in some environments and can cause the telecoil to pick up a buzzing, or clicking that interferes with the sound quality or even makes the telecoil unusable. For example, some car motors, some dimmer switches, some fluorescent lights, and some heavy electical equipment, some phones, or even building wiring can generate an annoying EMI signal.
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Some cellphones can also cause an RF interference from the protocol they use to communicate with cell towers.
Telecoils can provide that extra help you need to hear in many otherwise impossible situations. Ask your hearing health care provider about telecoils if you think they might help you. Don't count on your provider to suggest telecoils. They aren't something you have to buy as an extra, they are something that comes with better hearinga aids and most cochlear implants. You can learn more about loops and telecoils HERE.
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