Unlike our other senses — all of which rely on chemical processes — hearing is completely mechanical. Your ear translates sound waves into movement through the eardrum and tiny bones in the middle ear, and then electrical nerve impulses are sent to the brain.
Simple, right? Mostly, it is . . . until you get to the brain. Here, the processing of auditory signals becomes extremely complex. It’s through the brain’s interpretation of auditory signals that we receive intelligible communication through sound — and for the one in six adults who has trouble interpreting sounds, it’s usually something in this part of the process that breaks down, which is why auditory difficulties usually require much more than a quick fix.
How do the brains of individuals who misinterpret sounds work differently from those without hearing difficulties? For that matter, how do our brains interpret sounds in the first place?
Auditory Nerve Receptors:
The cochlea contains between 15,000 and 20,000 auditory nerve receptors, with each receptor connected to its own hair cell that detects sounds.
Each time a hair cell is activated, a burst of electrical impulses is sent to an area of the brain stem known as the cochlear nucleus, where the brain starts to make sense of these sounds
Groups of neurons in the brain determine the pitch of the sound based on the position of the hair cells that sent the electrical impulses.
Louder volumes cause greater vibration in the cochlea, meaning more hairs are stimulated and move with greater force.
New research is uncovering more about how language gets decoded in the brain, with different groups of synapses processing different types of sounds. One area, for instance, processes plosive sounds like p, t, k, b, and d, and another area processes fricative sounds like z, v, and s.
The following conditions could cause you to have trouble interpreting sounds:
SENSORINEURAL HEARING LOSS:
Definition: If a sound is loud enough, hair cells in the cochlea will break, leading to permanent damage. This means the brain doesn’t receive the signal it should (or it detects a much softer version of that signal). These interferences are the most common cause of hearing loss.
Treatment: Damage to the sensory hair cells is permanent, but amplification with hearing aids tuned specifically to the wearer’s hearing loss can vastly improve sound perception and ability to understand speech clearly.
Definition: Tinnitus is the perception of sound in the absence of external noise. There are many causes, but it is often brought about by hearing loss, with the brain trying to replace sounds that aren’t being received through the cochlear nerve. The result is the ringing, whistling, and hissing that are common complaints of sufferers.
Treatment: There are several types of treatment for tinnitus, ranging from counseling to devices designed to mask the tinnitus with other sounds. Many patients, however, see significant benefit from treating the hearing loss that is leading to their symptoms.
Definition: An oversensitivity to certain frequencies and volume ranges, hyperacusis makes some sounds seem unpleasant or painfully loud. The auditory nerves are selectively damaged, while the hair cells that pick up those tones remain intact, resulting in the brain’s inability to regulate sounds. Many with hyperacusis also complain of tinnitus, and vice versa.
Treatment: Counseling can help a patient retrain their reaction to overly loud sounds. Acoustic therapy can also help decrease a patient’s sensitivity to sounds over time.
AUDITORY PROCESSING DISORDER:
Definition: An auditory processing disorder is the inability to process information the same way others do, sometimes leading to difficulties recognizing or interpreting sounds and speech. It is thought that a dysfunction of the central auditory nervous system can cause an inability to correctly comprehend sound. A disruption during a sensitive period in auditory development may be the primary cause
Treatment: Effective solutions for APD must be highly individualized to address the specific deficit. Altering the communication environment, one-on-one training with a therapist, or assistive electronic devices can all help to improve speech comprehension.