Unit 4: Hearing

• place theory • frequency theory

What theories help us understand pitch perception?

Decibels

A unit of measurement of loudness (measuring unit for sound energy)

basilar membrane

vibrating membrane in the cochlea of the inner ear; it contains sense receptors for sound ( *hair cells* )

Cochlea

• a coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses

cochlear implant

• a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea • only way to restore hearing = ________

frequency theory

• in hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch - *best explains low pitches* - problematic = am individual neuron can't fire faster than 1000 times per sec ——> *volley principle* = neural cells can alternate firing

middle ear

• the chamber between the eardrum and *cochlea* containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea's oval window • transmits eardrum's vibrations thru a piston made of 3 tiny bones to the cochlea

Frequency

• the number of complete wavelengths that pass a point in a given time (Ex: per second) —> determines *pitch*

Audition

• the sense or act of hearing • like our other senses, ________ is highly adaptable

The outer ear is the viable portion of the ear. The middle ear is the chamber between the eardrum and cochlea. The inner ear consists of the cochlea, semicircular canals, and vestibular sacs. Thru a mechanical chain of events, sound waves traveling thru auditory canals cause tiny vibrations in the eardrum. The bones of the middle ear amplify the vibrations and relay them to the fluid-filled cochlea. Rippling of the basilar membrane, caused by pressure changes in the cochlear fluid, causes movement in the tiny hair cells, triggering neural messages to be sent (via the thalamus) to the auditory cortex in the brain. Sensorineural hearing loss (or nerve deafness) results from damage to cochlea's hair cells or their associated nerves. Conduction hearing loss results from damage to the mechanical system that transmits sound waves to cochlea. Cochlear implants can restore hearing for some people.

How does the ear transform sound energy into neural messages?

Organ of corti

Structure of surface of basilar membrane that contains receptor cells for hearing

- *amplitude* (strength) of waves determines loudness - *frequency* - *pitch* (Measure sounds in *decibels* ) (Ex: long waves = low frequency - low pitch)

What are the characteristics of air pressure waves that we hear as sound?

inner ear

the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs

pitch

• a tone's experienced highness or lowness; depends on frequency

auditory nerve

• bundle of neurons that carries signals from ear to Brain (bundle of nerves carrying sound to the brain )

sensorineural hearing loss

• hearing loss caused by damage to the cochlea's receptor cells or to the auditory nerves; also called nerve deafness (Could be Heredity) - disease can cause it, but more often culprits are biological changes linked to heredity, aging & prolonged exposure to ear-splitting noise or music

conduction hearing loss

• hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea (Ex: if eardrum is punctured or if tiny bones of middle ear lose their ability to vibrate, ear's ability to conduct vibrations diminishes )

place theory

• in hearing, the theory that links the pitch we hear with the place where the cochlea's membrane is stimulated - *Best explains high pitches* - *Hermann von Helmholtz's* —-> explains how we hear high pitches sounds—> not how we hear low