1. Chapter 4 Powerpoint: Hearing

2. Warm up
How do we hear?

3. Audition Audition Sound Frequency Pitch Decibels (Db)
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

5. 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

6. 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.

7. Parts of the Ear
Eardrum = 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.

8. The Intensity of Some Common Sounds
A recent U of Tenn. study found that 60 percent of college students suffer some high-frequency hearing loss
Loud music is believed to be the culprit
Live concerts—120 + decibels, louder than jack hammer, chainsaw
OSHA says that 85 decibels (food processor) 8 hours, 5 days a week will eventually cause permanent hearing loss
For each 5 decibel increase, the time it takes to cause lasting injury drops by half
Try: hold finger up as if taking a court room oath, rub thumb, finger together and should hear a scrtiching sound---if not, MAY have hearing loss

9. 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…

10. Sound Localization Tells us where sound is from Stereophonic hearing
Localization of sounds
Intensity
Speed of the sound
A just-noticeable difference in
direction corresponds to a
time-difference of sec!
If sound equidistant from both
ears it is harder to localize

11. Audition Conduction Hearing Loss Nerve Hearing Loss (Sensorineural)
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
Ringing in the ears is called tinnitus, affects more than 36 million Americans
Most common cause is exposure to loud noises, but also can be caused by certain drugs, ear infections, food allergies
In most severe form, this ailment is incapacitating
Cochlear Implant
Electronic device that translates sounds into electrical signals and sends it to brain
Can correct some sensorineural deafness
Only works if once could hear

12. Thinking Question:
How is hearing psychological?

13. Sound Lab
Answers follow…

14. 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.

15. 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.

16. 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.