Hearing

Anatomy of the Ear

How the Ear Works

The outer ear The pinna, which is the external part of the ear, collects sounds and funnels them through the auditory canal to the tympanic membrane (the eardrum), which marks the boundary between the outer ear and the middle ear

How the Ear Works The middle ear The malleus, incus, and stapes (also called the hammer, anvil and stirrup) vibrate in reaction to sound waves from the auditory canal The stapes’ movement creates vibrations on the oval window, which covers the inner ear

How the Ear Works The inner ear The cochlea contains in the basilar membrane about 16,000 hair cells that are the receptor cells for hearing Fluid in the cochlea is displaced, causing the hair cells to move, in turn causing the sensation of hearing When these hair cells or auditory nerve fibers are damaged, a person suffers nerve deafness Conduction deafness is hearing loss due to damage to the mechanical system carrying sound waves to the cochlea

What We Hear Loudness The dimension of auditory experience related to the intensity of a pressure wave. Pitch The dimension of auditory experience related to the frequency of a pressure wave. Timbre (pronounced “TAM-bur”) The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.

How We Distinguish Pitch Pitch is the quality of a sound perceived as high or low and is determined by the frequency of the sound wave Humans can perceive sound wave frequencies from about 20 to 20,000 Hertz Place theory contends that there is a specific place along the basilar membrane in the inner ear that will correspond to a particular frequency. Frequency theory contends that the frequency of a sound wave is mimicked by the firing rate of the hair cells across the entire basilar membrane

How We Distinguish Pitch Both theories have validity According to the volley principle, Frequency theory explains our perception of sound up to about 5000 Hz. Because 5000 times per second is the upper limit for the firing rate using the volley principle, Frequency theory would not be able to explain how we perceive higher frequencies Hence, Frequency theory explains the perceptions of lower pitched sounds ( 5000 Hz) For frequencies between 500 and 5000 Hz, both theories are correct, and hence we have better pitch perception in this range

From Sound Wave to Perception 1. Pinna  Tympanic Membrane (eardrum)  bones of inner ear (hammer, anvil, stirrup)  COCHLEA (primary hearing organ) 2. Cochlea is filled w/ fluid, which further transmits vibrations to thin membrane- Basilar Membrane 3. BM = Transduction; tiny hairs on BM tickle the sensory nerves 4. Neural message is sent to Temporal Lobe

Copyright © Allyn and Bacon 2006 How Sound Waves Become Auditory Sensations Tympanic membrane – The eardrum

Copyright © Allyn and Bacon 2006 How Sound Waves Become Auditory Sensations Cochlea – Where sound waves are transduced

Copyright © Allyn and Bacon 2006 How Sound Waves Become Auditory Sensations Auditory nerve – Neural pathway connecting the ear and the brain

Auditory Localization Sounds from different directions are not identical as they arrive at left and right ears Loudness Timing Phase The brain calculates a sound’s location by using these differences.

Copyright © Allyn and Bacon 2006

Conduction Deafness An inability to hear resulting from damage to structures of the middle or inner ear Conductive hearing loss is often only mild and is never worse than a moderate impairment. Generally, with pure conductive hearing loss, the quality of hearing (speech discrimination) is good, as long as the sound is amplified loud enough to be easily heard. Possible Causes Ear wax build up Fluid inside the inner ear, like from an inner ear infection. If the bones of the ear get a buildup of calcium

Sensorineural Deafness… or Nerve Deafness An inability to hear, linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers It can be mild, moderate, severe, or profound, to the point of total deafness. Possible Causes Long-term exposure to environmental noise Genetic Disease or illness Medications Physical trauma

Pre-Lingual Deafness These are people that are born deaf