1. Hearing: The Nature of Sound

2. Sound Sound, like light, comes in waves as Sound is vibration
Acoustical transduction: Conversion of sound waves into neural impulses in the hair cells of the inner ear
Features of sound include:
Pitch: sound’s highness or lowness, which depends on the frequency of the sound wave
Hertz: measure of the number of sound wave peaks per second. Hertz determines the pitch of a sound
Decibels: measure of the height of a sound wave, which determines the loudness of a sound

3. Two theories of hearing
Place theory- different frequencies of sound waves are said to vibrate different places on the cochlea. These places are wired to different parts of the auditory cortex in the brain so that the sound can be processed correctly
Frequency theory- the entire cochlea is believed to vibrate at a particular frequency, thus sending the signal of the quality of sound to the brain
100 Hz

4. Amplitude: The physical strength of a wave-the “volume” of the sound
Frequency & Amplitude
Frequency: The number of cycles completed by a wave in a given amount of time-determines pitch
Amplitude: The physical strength of a wave-the “volume” of the sound

5. Hearing: The Structure
of the
Auditory System

6. Divisions of the Ear Ear’s structure can be divided into:
Outer Ear: Pinna. Collects sounds
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
Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs

7. Cochlea
A hearing organ where sound waves are changed into neural impulses
The major organ of hearing
Filled with fluid; a snail shaped body tube

8. Auditory Canal
When your best friend shouts your name across campus, what happens? First, obviously, the vibrations that constitute the sound must travel through the air from your friend’s mouth to your ear. When the sound waves reach your ear, they travel down your auditory canal.
The opening through which sound waves travel as they move into the ear for processing
Ends at the tympanic membrane (eardrum)

9. Tympanic Membrane (eardrum)
The tissue barrier that transfers sound vibration from the air to the tine bones of the middle ear
Can be damaged by objects in the ear or exceptionally loud noises

10. Ossicles
Three tiny bones that transfer sound waves from the eardrum to the cochlea
Hammer, anvil and stirrup

11. Oval Window
The point on the surface of the cochlea which receives the sound vibration from the ossicles
As the oval window vibrates, the fluid in the cochlea vibrates

12. Similar to the rods and cones within the eye
Hair Cells
The receptor cells for hearing in the cochlea that change sound vibrations into neural impulses
Similar to the rods and cones within the eye

13. Auditory Nerve
The nerve that carries sound information from the ears to the temporal lobes of the brain

14. Semicircular Canals
Organs in the inner ear used in sensing body orientation and balance (vestibular sense)
Relies on fluid in the canals
Spinning in circles disrupts the fluid

15. The Process of Hearing
1.) The middle ear transmits the eardrum’s vibrations through a “piston” made of 3 small bones (the hammer, anvil and stirrup) to the cochlea (snail shaped tube)
2.) The incoming vibrations cause the cochlea’s membrane (oval window) to vibrate, moving the fluid that fills the tube. This motion causes ripples in the basilar membrane (hair cells)
3.) The movement of cells triggers impulses in the adjacent nerve fibers which from the auditory nerve that connects via the thalamus to the temporal lobe

16. Hearing: Sound Localization

17. Localization of Sound Locating where sound is originating from
Done through two cues:
Which ear hears the sound first? (sound travels through the air at about 750 mph)
Which ear hears the louder sound?
By the time a sound gets around to the ear farther from the source, the sound is muted enough for your brain to be aware of the difference.

18. Hearing Deficits
Older people tend to hear low frequencies well but suffer hearing loss when listening for high frequencies

19. Deafness
Conduction deafness- involves a blockage of the sound as it travels through the ear. Earwax, foreign objects, and damage to the eardrum or ossicles are the main causes of this kind of deafness
You can replace the bones or get a hearing aid to help
Nerve (sensorineural) deafness- involves damage to the auditory nerve.
Illness, genetic determination, loudness, or traumatic head injuries
NO WAY to replace the hairs
Cochlea implant is possible
---Cochlear implants are electronic devices that enable the brain to hear sounds