Anatomy & Physiology

The ability to hear is important to just about all living creatures; even though scientists have discovered many species of blind fishes, amphibians, reptiles, and mammals, no deaf vertebrate species have been identified. That said, hearing doesn’t necessarily call for ears. Only vertebrate animals have ears, whereas invertebrate animals utilize various other sense organs in order to recognize the vibrations we know as audio waves. In the case of insects, they have extremely sensitive tympanal organs which offer excellent hearing capabilities. Certain fly species can locate their prey exclusively via its song from a substantial distance. Spiders and cockroaches have tiny hairs on their legs that they use to pick up sounds, and caterpillars have similar sound-receiving hairs on their bodies. One species known for its acute hearing is the elephant. Elephants have large ears, but they can also hear through their feet. This form of hearing is so acute that elephants can detect the sound of thunderstorms or the low-frequency call of other elephants coming from many kilometers away.

Central Auditory Processing Disorder, or CAPD, is a hearing disorder in which the trouble lies not with the ears, but with the brain. The person with CAPD hears sounds correctly but something adversely affects the way their brain recognizes and interprets the sounds, especially the sounds associated with speech. That’s why the disorder is sometimes summarized as an ear-brain coordination problem. Central Auditory Processing Disorder is a condition that afflicts an estimated 2% to 5% of children of school age, and as many as 50% of children who have been diagnosed as having a learning disability. Children with CAPD often fail to recognize subtle differences between the sounds of different words, even though the words are clear and loud enough for them to hear. This inability to understand words often becomes worse in noisy environments, but is not as present in quiet environments.

As hearing professionals, one of the sometimes frustrating things we encounter in our practice is that the issues that have caused hearing problems in our patients cannot be reversed. For example, one of the extremely common causes of hearing loss is damage to the tiny, sensitive hair cells that line the inner ear and vibrate in response to sound. What we think of as hearing are the translations of these vibrations into electrical impulses which are sent to and interpreted in the brain.

To begin with an attempt at humor, the “speech banana” isn’t a reference to the old skit, “Speak up…I can’t hear you…I’ve got a banana in my ear.” The “speech banana” is a distinctive design appearing on an audiogram. In an audiogram, you usually see the frequency (measured in Hertz) on the x axis, and the loudness (measured in Decibels) on the y axis. The expression ‘speech banana’ comes from the banana-shaped cluster of points on the audiogram that arises when human language is analyzed. The spoken sounds of most of the letters of the alphabet together with the letter combinations ch, sh, th and ng all fall within this area.