1. Auditory System: Sound

2. The Stimulus Input: Sound Waves
Sound, like light, comes in waves, which are characterized by their frequency (pitch) and amplitude (decibels). The height of the wave gives us the amplitude of the sound. The frequency of the wave gives us the pitch of the sound.
Sound is vibration. The vibrational energy of vibrating objects, such as guitar strings, transfer the surrounding medium-air as the vibrating objects push the molecules of the medium back and forth. In space, there is no air, so the sound wave would have no medium to push. Any explosion, for example, would be eerily without sound.
Frequency --> number of cycles completed
by a wave in a given amount
of time determines pitch
**Pitch --> sound’s highness or lowness
measured as hertz (Hz)
High pitched sounds
Amplitude --> physical strength of a
wave--the “volume” of a
sound; measured in
decibels
Low pitched sounds

3. The Stimulus Input: Sound Waves
Locating where sound
is originating from
requires two cues:
--Which ear hears
the sound first?
the louder sound?

4. The Stimulus Input: Sound Waves
4,186 Hz Highest note on a piano
1,000 Hz Highest pitch of human voice
100 Hz Lowest pitch of human voice
27 Hz Lowest note on a piano

5. The Stimulus Input: Sound Waves
Discovering PSY p. 94 Figure 3.7
Above are examples of Frequency & Amplitude/decibels
Timbre – distinctive quality of a sound determined by the complexity of the wave and its different combinations of frequencies. (Figure C is more complex than Figures A or B)

6. Distinguishing Pitch
Frequency theory -- basilar membrane vibrates at the same frequency as the sound wave
The higher the frequency wave, the faster the firing of hair cells
Theory used to explain how you hear low frequencies
Place theory -- different frequencies cause larger vibrations at different locations along the basilar membrane
Different pitches stimulate different areas on the basilar membrane
The brain receives these messages and interprets them as different pitches
Theory used to explain how you hear high frequencies
Use both theories when you listen to sounds with both high and low frequencies

7. Auditory Masking
Piccolo, soft
Bassoon, loud
Piccolo, loud
Bassoon, soft
Distance along basilar membrane
(a)
(b)
Effect of bassoon on basilar membrane
Vibration
amplitude
of basilar
membrane
Effect of piccolo on basilar membrane
Low frequency sounds effectively mask high frequency sounds
High frequency sounds cannot effectively mask low frequency sounds
Hockenbury Powerpoint (schulman)

8. Visual Capture The most accessible example is a movie theater.
Imagine being in a movie theater. Where does the
sound originate? The sides of the room we are in,
because we can picture in their minds the big
speakers hanging on the sides of the movie
theater. When we are watching a movie, we
believe the sound comes from the front of the
room. When the actors are talking on-screen, the
sound appears to come from their mouths because
of visual capture - the eyes overrule the ears.
Hockenbury Powerpoint (schulman)

9. The Process Of Hearing (How Sound Waves Become Auditory Sensations)
Auditory perception occurs when sound waves
interact with the structures of the ear
Audition (sense of hearing) results in sound waves
being collected in the outer ear, amplified in the middle
ear, and converted to neural messages in the inner ear.
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).
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).
The movement of cells triggers impulses in the adjacent nerve fibers which form the auditory nerve that connects via the thalamus to the temporal lobe.

10. Parts Of The Ear

11. Parts Of The Ear Revisited
Hockenbury Powerpoint (schulman)

12. Anatomy Of The Cochlea: Another View
Outer ear
Middle ear
Inner ear
A sound causes
the basilar
membrane to wave
up and down
Basilar
membrane
Hair cells
Tectorial
Round window
Eardrum
Oval window
Cochlea,
partially
uncoiled
Stirrup
Anvil
Hammer
Sound
waves
Auditory
canal

13. Parts Of The Ear
Pinna --> Sounds waves enter it and are funneled to the auditory canal
Auditory Canal --> Connects the outer ear with the eardrum (tympanic membrane)
Ear Drum --> Tissue barrier that transfers sound vibrations to the ossicles; can be damaged by
objects in the ear or exceptionally loud noises
Ossicles (hammer, anvil, stirrup) --> Three tiny bones that transfer sound waves from the ear drum
to the cochlea; in old age, they may become brittle or damaged,
resulting in conduction deafness
Oval window --> 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, moving hair
cells along the basilar membrane
Cochlea --> A hearing organ where sound waves are changed into neural impulses
Hair cells --> Receptor cells for hearing in the cochlea that change sound vibrations into neural
impulses. When they move, they trigger action potential in the base of the hair cell
(transduction).
--Similar to the rods and cones within the eye
--If these are damaged (due to prolonged loud noises), then you have nerve deafness
which cannot be helped by a hearing aid.
Auditory Nerve --> Stimulated by the hair cells in the basilar membrane of the cochlea, it carries
sound information from the ears to the thalamus then to the auditory cortex in the
temporal lobes of the brain

14. Position And Movement
Vestibular sense: The sense of body orientation with respect to gravity
The receptors for this information are tiny hairs in the semicircular canal of the inner ear

15. Types Of Hearing Loss (Deafness)
Conduction Hearing Loss --> Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.
Surgery
Sensorineural Hearing Loss --> Hearing loss caused by damage to the cochlea’s receptor cells (i.e. hair cells) or to the auditory nerve, also called nerve deafness.
Hearing aid to amplify sound
Cochlear Implant