Chapter 4 Powerpoint: Hearing

Warm up

How do we hear?

Audition Audition

the sense of hearing Sound

Sound is the psychological experience that occurs when a change in air pressure is detected by our outer ear. The frequency and amplitude of sound waves determine what the sound “sounds like”

Frequency the number of complete wavelengths that pass a point in a given time

Pitch a tone’s highness or lowness depends on frequency

Decibels (Db) How we measure hearing Zero decibels is absolute threshold for hearing (arbitrary) Every 10 decibels corresponds to 10 fold increase in intensity

The brain transforms sound waves into nerve impulses that our brain interprets.

• (a) The outer ear funnels sound waves to the eardrum. The bones of the middle ear amplify and relay the eardrum’s vibrations through the oval window into the fluid-filled cochlea. (b) the resulting pressure changes in the cochlear fluid cause the basilar membrane to ripple, bending the hair cells on the surface. Hair cell movements trigger impulses at the base of the nerve cells, whose fibers converge to form the auditory nerve, which sends neural messages to the thalamus and on to the auditory cortex.

How does the ear work video

Audition- The Ear Inner Ear

innermost part of the ear, containing the cochlea, semicurcular canals, and vestibular sacs. Carries info to The brain to be analyzed

Middle Ear chamber between eardrum and cochlea

containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window. Vibrates in response to pressure changes

Outer Ear Part of ear where sound waves enter. Made up

of auditory canal and ear drum. Collects passing changes in air pressure.

Parts of the EarEardrum = tight membrane that vibrates when struck by sound waves.

Bones of the middle ear = the hammer, anvil, stirrup which vibrate with the eardrum.

Oval window = where the stirrup connects to the cochlea.

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

Auditory nerve = nerve which sends the auditory message to the brain via the thalamus.

The Intensity of Some Common Sounds

Audition Place Theory (Helmholtz)

the theory that links the pitch we hear with the place where the cochlea’s basilar membrane is stimulated.

Was found (Bekesy, 1957) that the cochlea vibrates in response to sound. Vibrations are at different places on the membrane, depending on the pitch.

Better explains high pitched sounds b/c low pitch sounds not neatly localized on basilar membrane

Frequency Theory 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 Frequency of neural impulses on auditory nerve translates to pitch Problematic because a neuron cannot fire faster than 1000 times/ second but

we can sense sounds with frequencies higher than 1000 waves per second! (unless we follow volley principle…. Alternate firing… some neurons fire while some reload….)

The best theory to explain hearing is probably a combination of both…

Sound Localization• Tells us where sound is from• Stereophonic hearing• Localization of sounds

– Intensity– Speed of the sound

• A just-noticeable difference indirection corresponds to a time-difference of .000027 sec!

• If sound equidistant from bothears it is harder to localize

Audition Conduction Hearing Loss

hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea (punctured eardrum/ wax, etc)

Nerve Hearing Loss (Sensorineural) hearing loss caused by damage to the cochlea’s

receptor cells or to the auditory nerve Heredity, aging, noise exposure

Cochlear ImplantElectronic device that translates sounds into electrical

signals and sends it to brainCan correct some sensorineural deafnessOnly works if once could hear

Thinking Question:

How is hearing psychological?

Sound Lab

• Answers follow…

5 qualities of sound (psychoacoustics)

• Pitch - (also associated with frequency), the perception of a high or low sound.

• Loudness - (also called amplitude), the intensity of a sound.• Phase - the increase and decrease in pressure cycle any single

vibration.• Direction - (hearing with two ears creates left/right, high/low,

front/back qualities), first come first heard by one ear or the other.• Distance - (also associated with reverberation time), perception of

how near or far away a sound's source is.• Timbre - (also called tone color), the perceived quality of any

sounds' multiple frequencies changing through time.

How does Phone Work• How the Telephone Works• When a person speaks into a telephone, the sound waves created by his

voice enter the mouthpiece. An electric current carries the sound to the telephone of the person he is talking to. A telephone has two main parts: (1) the transmitter and (2) the receiver.The Transmitter of a telephone serves as a sensitive "electric ear." It lies behind the mouthpiece of the phone. Like the human ear, the transmitter has an 14 eardrum." The eardrum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds, depending on the variations in air pressure caused by the varying tones of the speaker's voice.

How does record player work

• As you probably know, sound is made up of vibrations.

The surface of the record is carefully pressed to make the needle of the record player vibrate in exactly the right way to recreate the music. These vibrations are then amplified so you can hear them.