HEARING Module 20

Hearing – sound waves  Audition – the sense or act of hearing  Frequency – the number of complete wavelengths that pass a point in a given time; determines pitch  Pitch – a tone’s experienced highness or lowness; depends on frequency  Amplitude – the height of the waves determines loudness  Sound energy is measured in decibels  Absolute threshold=0 decibels  Normal conversation=60 decibels  Whisper=20 decibels  Prolonged sounds above 80 decibels = hearing loss

The Ear  Sound waves enter the outer ear and are channeled through the auditory canal to the eardrum.  Eardrum – tight membrane that vibrates with the sound waves  Middle ear – the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window  Inner ear – the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs

Cochlea  Cochlea – a coiled bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger neural impulses  The motion of these impulses causes ripples in the basilar membrane which is lined with hair cells  Cilia – hair cells that bend, triggering neural impulses in the adjacent nerve fibers to form the auditory nerve which sends the message via the thalamus to the auditory cortex in the temporal lobe.  Hair cells – extremely sensitive and quick

Hearing loss  Sensorineural hearing loss – caused by damage to the cochlea’s receptor cells or to the auditory nerves; also called nerve deafness  Linked with heredity, aging, and prolonged exposure to loud sounds (over 100 decibels)  Bent hair cells  Ringing in ears – alert that there is damage  Cochlear Implant – a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea  Helps restore hearing for most adults  Will not enable hearing in adults if their brains never learned to process sounds during childhood  Highly debatable when used in children  Conduction hearing loss – caused by damage to the mechanical system that conducts sound waves to the cochlea

Perceiving loudness  Brain interprets loudness from the number of activated hair cells  Hard of hearing – still hear loud sounds – only want soft sounds amplified through hearing aids Locating Sounds  Sound waves strike one ear sooner and with more intensity than the other  It is not easy to detect location of sounds equidistant from both ears

Perceiving pitch  Place Theory – links the pitch we hear with the place where the cochlea’s membrane is stimulated  Hermann von Helmholtz  Determines how we hear high pitched sounds  Frequency Theory –the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch  Volley principle  Determines how we hear low pitched sounds  Combination of place and frequency seems to handle the pitches in the intermediate range