DEAR DOCTOR K:
My hearing is going. Before I get a hearing aid, I’m told I need a hearing test. How will the test help?
The hearing test (formally called an “audiological evaluation”) identifies how bad your hearing loss is in each ear. It also determines where the problem is worst. Is it with high-pitched sounds? Is it in distinguishing a particular sound — like someone speaking to you — in a noisy place? This is what the audiologist (a health professional specializing in hearing testing and hearing aids) needs to know in order to tell if you could benefit from a hearing aid and, if so, which style and type would help the most.
Before describing a hearing test, I need to first explain how the ears and the brain hear. 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. (I’ve put an illustration of how we hear below.)
Figure 2: How we hear
Sound travels in waves through the air (A) into the ear canal (B), where it is amplified and causes the eardrum to vibrate (C). The eardrum vibrates the tiny bones known as ossicles (D), which transmit the vibrations through the membrane-covered opening called 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 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 is tested separately by sounds of different frequencies and decibel levels. Frequency is the pitch of a sound. A high-pitched sound is like a violin playing a high note. A low-pitched note is like the lowest keys on a piano. 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.
- 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.
- 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. This test assesses how well you understand words. A high score on this test means that your problem in understanding a spoken word comes from not hearing the word loudly enough. A hearing aid can correct that problem.
Today’s technology for testing 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 have greatly improved the quality of their lives.