SAP - Theories of Hearing and Deafness Lesson

Theories of Hearing and Deafness

High and low pitched sounds are determined by the frequency of a sound wave. The basilar membrane is a key component in our ability to hear pitch. There are two theories that describe its role in determining sound.

Helmholtz's Place Theory

This theory states that we hear different pitches because sound waves trigger different hairs to vibrate at various places along the basilar membrane. High-frequency sounds have a maximum vibration near the stirrup end of the basilar membrane, while low-frequency sounds have the opposite effect. This theory accounts for both high and low-frequency sounds.

Frequency Theory

The frequency theory states that the basilar membrane vibrates the incoming sound waves by triggering neural impulses at the same rate as the sound wave. It explains how we hear low-pitched sounds. A sound wave of 100 hertz causes vibrations 100 times per second. One problem with this theory is that neurons cannot fire more than 1000x per second, but some wave frequencies are above 1000 waves per second.

Cochlear Implant: Sound processor Internal implant Hearing nerve Cochlea Electrode

Deafness

When someone is deaf or partially deaf, they experience a lack of hearing. Two theories are proposed to explain different types of deafness.

  1. Conduction Deafness or Conduction Hearing Loss is when the eardrum is punctured, or something goes wrong causing the tiny bones in the middle ear to lose the ability to vibrate. When this happens, it is difficult to hear any tones. To counter this effect hearing aids can be used. They produce amplified vibrations.
  2. Nerve Deafness or Sensorineural Hearing Loss is caused by disease, age, or overexposure to loud sounds (85 decibels or above). In this type of deafness, the hair cells in the cochlea become damaged or destroyed. Once damaged they remain dead. However, a cochlear implant can be surgically placed to bypass the damaged portion of the ear and directly stimulate the auditory nerve.

 Please take a moment to view the following video on Cochlear Implants.

 

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