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Chapter 4.3

PSY100H1 Chapter Notes - Chapter 4.3: Amygdala, Limbic System, Stirrup

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Michael Inzlicht

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Module 4.3 The Auditory System
- Certain scientists believe that we are hard-wired to not just to hear music, but also to feel a
significant emotional connection to it
- Levitin also argues that human identity has music at its core, and that common themes in music
include love, friendship, knowledge, religion, relationships, and joy
Sound and the Structures of the Ear
- Function of the ear: is to gather sound waves
- The function of hearing: is to extract some sort of meaning from those sound waves
- The ear detects sound waves and transforms the info into neural signals
- Sound waves are simply changes in the mechanical pressure transmitted through solids, liquids,
or gases
- Sound waves have two important characteristics: frequency and amplitude
o Frequency: refers to wavelength and measured in hertz (Hz), the number of cycles a
sound wave travels per second
o Pitch: the perceptual experience of sound wave frequencies
- High-frequency sounds (tires screeching) have short wavelengths and a high pitch
- Low-frequency sounds (bass guitar) have long wavelengths and a low pitch
- Amplitude: determines its loudness
o High-amplitude sound waves are louder than low-amplitude waves
o Both types of info are gathered and analyzed by ears
- Humans are able to detect sounds in the frequency range from 20-20,000 Hz
- Loudness (a function of sound wave amplitude) is typically expressed in units called decibels
The Human Ear
- Human ear is divided into outer, middle, and inner regions
- Pinna: the outer (visible) region that helps channel sound waves to the ear and allows you to
determine the source or location of a sound
- Auditory canal: extends from pinna to eardrum
- Middle ear consists of three tiny moveable bones called ossicles:
o Malleus (hammer)
o Incus (anvil)
o Stapes (stirrup)
- Movement of eardrum due to sound vibration moves the ossicles
- The ossicles attach to an inner ear structure called the cochlea
o Cochlea: a fluid-filled membrane that is coiled in a snail-like shape and contains the
structures that convert sound into neural impulses
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- Converting sound into neural impulses is possible because of hair-like projections that line the
basilar membrane of the cochlea
- The pressing and pulling actions of the ossicles causes parts of the basilar membrane to flex.
This causes the fluid in the cochlea to move the hair cells. When the hair cells move, they
stimulate the cells that comprise the auditory nerves and these nerves (made of neurons) fire
as a result of hair cell movement
- The auditory nerves send signals to the thalamus and then to the auditory cortex (located in
temporal lobe)
- Damage to any part of this system can cause hearing impairments
o Cochlear implants are now used to help people regain some of their hearing
A small microphone that detects sound and electronically stimulates parts of the
membranes in the cochlea
Really helpful for kids
The Perception of Sound
Sound Localization: Finding the Source
- Accurately identifying and orienting oneself toward a sound source has some obvious adaptive
o Eolutioarily, failure to do so ould result i a orgais eoig soeoe else’s
dinner or failing to catch dinner
- Sound Localization: the process of identifying where sound comes from
o Sound localization is handled by parts of the brain stem as well as by a midbrain
structure called the inferior colliculus
- Two ways that we localize sound:
o 1) We take advantage of the slight time difference between a sound hitting both ears
to estimate the direction of the source
If your friend shouts your name from your left side, the left ear will receive the
info a fraction of a second before the right ear
o 2) We localize sound by using differences in the intensity in which sound is heard by
both ears
Phenomenon known as sound shadow
If the origin of sound is at your left, the left ear will hear it with more intensity
because the right ear will be in the sound shadow
- The inferior colliculi detect differences in the times when sound reaches the left versus the
right, as well as intensity to identify origin
Theories of Pitch Perception
- How does the cochlea pave the way for pitch perception?
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