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Lecture 15

PSYCO104 Lecture Notes - Lecture 15: Chemical Substance, Olfactory Bulb, Menstrual Synchrony

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Eric Legge

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PSYCH 104 – LECTURE #15 – Sensation and Perception Pt. III
Sensory Processing in the Ear
o3 major parts
1. Outer (external) Ear
Sound waves travel into auditory canal leading to eardrum (movable
membrane that vibrates in response to sound waves) – aka tympanic
2. Middle Ear
Ossicles: Hammer (malleus), anvil (incus), stirrup (stapes)
Amplifies sound waves
A. Hammer is attached to ear drum
B. Stirrup attached to oval window (boundary between middle and inner ear)
3. Inner Ear
Cochlea: Coil-shaped structure containing sound receptors and filled with
Contains basilar membrane: Runs length of cochlea and
contains organ of Corti
oOrgan of Corti: Embedded in basilar membrane
containing hair cell receptors for sound
Hair cells synapse with neuron to auditory nerve
Nerve sends impulses via auditory relay station in thalamus to
auditory cortex
How are sound waves transmitted?
1. Sound waves strike eardrum
2. Pressure created at oval window by ossicles sets fluid inside cochlea into motion
3. Basilar membrane vibrates and membrane above it
4. Hair cells in organ of Corti bend and triggers release of neurotransmitters in neurons
of auditory nerve
Theories of Hearing (Pitch Perception)
1. Place Theory: Sound frequencies are coded in portion of basilar membrane where
fluid varies in cochlea peaks. Account for perception of frequencies >4000 Hz
Perception of pitch correspond to vibration of different portions
2. Frequency Theory: Number of nerve impulses sent to brain by hair cells of cochlea
corresponds to frequency of sound waves; is accurate at low frequency
oWhich theory is correct?
Depends on PLACE AND FREQUENCY coding of vibrations
Low frequency tones appear to be translated into pitch through
frequency coding
High frequency pure tones appear to rely on place coding
Complex tones depending on complex combinations of place and
frequency coding
Perceiving Sources of Sound
oAuditory (sound) localization: Locating source of sound in space
Sounds arrive first and loudest at ear closest to the sound
If in front, reaches both ears at the same time and intensity
There are extremely minute time differences of when a sound reaches
each of the ears
When we can’t hear
o1 in 1000 people are deaf
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