DEAR DOCTOR K:
I’m losing my hearing so my doctor has scheduled an audiological evaluation. What will this evaluation tell me?
An audiological evaluation identifies the severity of your hearing loss and the frequency range in which it occurs. This information may help identify the cause of your hearing loss. It’s also essential for determining whether you could benefit from a hearing aid and, if so, which style and type would help the most.
When a sound wave enters your ear, it hits the eardrum. Several tiny bones transmit sound waves from the eardrum through fluid, into the inner ear. There lies a snail-shaped organ called the cochlea that is covered with tiny hairs. These hairs generate electrical signals that travel along the hearing nerve (the auditory nerve) to the brain. (See illustration.)
How we hear
Sound travels in waves through the air (A) into the ear canal (B), where it is amplified and vibrates the eardrum (C). The eardrum vibrates the tiny bones known as the ossicles (D), which transmit the vibrations through the oval window and into the fluid in the cochlea in the inner ear.
The cochlear fluid (E) moves in waves, setting in motion the sensory hair cells inside the organ. The hair cells release electrochemical signals that travel along more than 30,000 auditory nerve pathways into the brain (F).
The evaluation is done by a hearing specialist, or audiologist, in a specially constructed booth that shuts out all unwanted noise. It tests the different parts of the ear that are necessary for hearing:
- Pure-tone test. Each of your ears, in turn, is exposed to sounds of different frequencies and decibel levels. (Frequency is the pitch of a sound. A decibel is the measurement of the loudness of a sound.) The pure-tone test identifies the quietest tones that you can hear at different frequencies.
- Next is a bone-conduction test. This test helps establish whether your hearing loss is primarily sensorineural (caused by damage to the cochlea, hair cells or auditory nerve) or conductive (caused by a blockage of sound transmission through your outer or middle ear), or a combination of the two. This test will also help determine whether your hearing loss can be medically corrected, and the kind of hearing aid you need.
Two additional tests will evaluate how well you hear and understand spoken words:
- Speech reception threshold test. You will hear words, instead of tones, through your earphones. The words start out loud and gradually get softer. The test identifies the decibel level at which you can understand and repeat only half of the words.
- Speech discrimination test. With age, many people can hear words loudly but not clearly. A speech discrimination test assesses how well you understand words. A high score on this test means that you are likely to benefit from a hearing aid. That’s because your problem in understanding a spoken word comes from not hearing the word loudly enough, and a hearing aid can amplify the loudness of sounds.
Today’s technology for testing your hearing has improved greatly since I was in medical school. Even greater advances have been made in hearing aids. They not only work better but they’ve also become tiny — people often don’t notice you have one. For many of my patients, hearing tests followed by the right hearing aid has greatly improved the quality of their lives.