Hearing Loss Explained

Hearing is a complex process that involves many parts of the ear working together to convert sound waves into information that is sent to the brain where that sound is interpreted and understood.

The ear consists of three main parts:

Simply put, sound, which includes speech, enters the ears and is received and moved along a defined pathway to the auditory areas (or hearing centers) of the brain where that sound is understood. The different parts of the ear and rest of the auditory pathway act as way stations by reacting to and moving sound to the next way station in the hearing system. Any time there is a disruption to the travel of sound as it makes its way to its final destination, the auditory areas of the brain, the result is a hearing loss or disorder. The outer ear, middle ear, inner ear and auditory centers of the brain all make up the auditory system. Here’s how it works:

• The outer ear collects sound waves moving through the air and directs them to the eardrum.
• The eardrum vibrates with sound.
• Sound vibrations move from the eardrum through the ossicles (bones in the middle ear) to the cochlea.
• Sound vibrations cause the fluid and tiny hair cells inside the cochlea to move.
• Hair cell movement creates neural signals, which are picked up by the auditory (hearing) nerve.
• The auditory nerve sends signals to the auditory areas (or hearing centers) of the brain, where they are interpreted as sounds and speech.

So, while sound is received by the ear, it is actually heard in the brain.

The speech banana is a term used to describe the area where the sounds of human speech (called phonemes), appear on an audiogram (graph of an individual's hearing thresholds). When the phonemes are plotted out on the audiogram they make the shape of a banana. Therefore, audiologists and other speech professionals refer to that area as the “speech banana.” While many other sounds fall outside of the speech banana, audiologists are most concerned with the frequencies within the speech banana because a hearing loss in those frequencies can affect a child's ability to learn language.

Hearing loss may result if any part of the hearing process along the auditory pathway is not functioning properly, which causes a disruption to sound as it travels towards the brain. The cause can be genetic, environmental, due to illness or even unexplained.

• Genetic - In more than 50 percent of pediatric hearing loss cases, it is believed that genetic factors are the cause. Genetic or hereditary hearing loss occurs when a gene from one or both of the parents affects any portion of the outer, middle or inner ear, causing varying degrees of hearing loss.
• Prenatal Exposure - In some cases, an in utero infection, illness, or toxin during the mother’s pregnancy can be passed on to a baby in utero and cause hearing loss.
• Perinatal Experiences - Procedures performed or medications used to save a baby’s life in an emergency (such as use of a ventilator or a strong antibiotic) can also affect hearing.
• Acquired Hearing Loss - When hearing loss occurs after birth, it is often due to factors such as:
  
  • Chronic ear infections, also called otitis media: A common issue for many children and typically causes only temporary hearing loss. However, prolonged issues without treatment or repeated cases can affect hearing and cause more permanent damage.
  • Ototoxic drugs: Usually prescribed to treat serious problems such as meningitis, this class of medications can affect hearing.
  • Disease: Conditions such as otosclerosis, Ménière's disease, meningitis and mumps can affect hearing. The impact on hearing varies depending on the cause, severity and duration of treatment.
  • Head injury: Head trauma can potentially have a dramatic effect on hearing, especially in children who are still growing.
  • Perforated eardrum: Ear infections, head trauma or the insertion of a foreign object into the ear (small toys, pens, cotton swabs, ear candles, etc.) can damage the eardrum. Oftentimes, a perforated or torn eardrum will heal with proper treatment and the accompanying hearing loss may be temporary.
• Unknown Causes - In some cases, it may be impossible to pinpoint why your child is deaf or hard of hearing. Regardless of the cause, it is important to act quickly to confirm a diagnosis, and ensure your child has auditory access to speech and language as early and consistently as possible.