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Chapter 8

Chapter 8 detailed

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Department
Psychology
Course Code
PSYB65H3
Professor
Ted Petit

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Chapter 8
[HEARING AND LANGUAGE PROCESSING]
Module 8.1: The Auditory System
Language production was one of the first cognitive abilities to be localized
in the brain
The Properties of Sound
Frequency rate of vibration / the number of wave cycles completed per unit of time
Measured in Hertz (Hz) cycles / second
Human ear can perceive vibrations between 20-20,000 Hz
Maximally sensitive to sounds between 1000 and 4000 Hz (human voice)
Codes for pitch
High frequency = high pitch
Low frequency = low pitch
Range of frequency that an animal perceives varies widely across species
Loudness corresponds to the amplitude (intensity) of the sound wave
Waves of different amplitudes differ in the degree to which the high point
(condensation of air) and the low point (rarefaction of air) of the wave differ from
each other
Measured in decibels (dB) sound pressure of a source when compared to a standard
intensity of 10-12 watts
Conversation: 40-60dB
Timbre complexity of sound
Fourier analysis a mathematical process in which complicated sounds are broken
down into simple component waves
Used to compress complex sounds on computers (MPEG-1, MP3) so that the
series of simple wave forms can be efficiently represented
The Ear
Transduction the ear detects and amplifies very subtle vibrations and transforms
these vibrations into neural signals
Transduction Mechanism:
Sound enters funnellike outer ear, passing through the pinna (outermost visible
portion of the ear) through the hole (auditory meatus) which leads to the external
ear canal
External ear canal amplifies vibrations and channels them to tympanic membrane
(ear drum)
Tympanic membrane vibrates and passes the vibration along the three bones of the
middle ear: malleus, incus, stapes
Collectively, the bones are referred to as ossicles
Each successive bone further amplifies the vibration, and transmits the
vibration through the oval window
Vibration of oval window (which is attached to the stapes) causes liquid vibrations
within the cochlea (filled with cochlear fluid)
www.notesolution.com
Chapter 8
[HEARING AND LANGUAGE PROCESSING]
Vibration of cochlear fluid causes the bending of basilar membrane and tectorial
membrane elicits neural activity in hair cells
Hair cells are receptor cells of auditory system; connects with
vestibulocochlear nerve
Anatomical Divisions of the Ear:
Outer Ear pinna, external ear canal
Catches and amplify sound waves
Middle Ear chamber between tympanic membrane and oval window
Sound waves are transduced from variations in air pressure into mechanical
energy that is propagated and amplified along the ossicles to the oval window
Inner Ear mechanical energy is turned into neural activity
Cochlea contains inner hair cells and outer hair cells
oOuter hair cells outnumber inner hair cells by 3:1
oInner hair cells serve as receptors for auditory system; only 5% of
auditory nerve cells receive inputs from outer cells
oOuter hair cells modulatory role; helps to tune the cochlea
through contraction and relaxation
Inner Hair Cells (auditory receptors) have tiny filaments at their tips cilia that are
arranged in order of height
Tallest cilia kinocilium
When cilia move toward direction of kinocilium: Fibers are stretched,
increased firing in axons of cochlea nerve
When cilia move away from kinocilium (in very quiet situations): firing in
cochlear nerve falls below the normal (resting) rate
Organ of Corti: Hair cells + their cilia + support cells
Different parts of the cochlea respond maximally to different frequencies
Basilar membrane closest to oval window is quite stiff, receptors are exposed
to higher frequencies
Near the helicotrema (apex), the basilar membrane is more flexible, receptors
are exposed to lower frequencies
Efferent projections from the cochlea demonstrate different activation under
different attentional conditions
Inner ear functions can be affected by higher perceptual and attentional
pathways
Auditory Pathways
Pathway #1
1.Axons of cochlear nerve form a branch of vestibulocochlear nerve which synapses
on the ipsilateral cochlear nuclei
2.Pathway A: Most projects lead to ipsilateral or contralateral superior olives
Projections travel ipsilaterally to the inferior colliculus
www.notesolution.com
Chapter 8
[HEARING AND LANGUAGE PROCESSING]
Pathway B: some lead directly to inferior colliculus of the midbrain
3.At the inferior colliculus,
Some projects cross the to the contralateral side eventually projects to
medial geniculate nucleus of thalamus, then to primary auditory
cortex
Some project to the medial geniculate nucleus of the thalamus, then to
primary auditory cortex
Unlike visual system, auditory projections do not necessarily terminate in the cortex
contralateral to their origins
Projections may cross contralaterally at the level of cochlear nuclei and at
level of inferior colliculus
Majority of all auditory projections are exclusively ipsilateral
Most fibres cross sides before the projections reach the cortex
Pathway #2
1.Axons of cochlear nerve form a branch of vestibulocochlear nerve which synapses
on the ipsilateral cochlear nuclei
2.Pathway A: Most projects lead to ipsilateral or contralateral superior olives
Projections travel ipsilaterally to the inferior colliculus
Pathway B: some lead directly to inferior colliculus of the midbrain
3.At the inferior colliculus, projections synapse on the dorsal medial geniculate
nucleus of the thalamus, then project directly to the secondary and tertiary
auditory cortices (BA42, BA22)
Auditory Cortex
Primary Auditory Cortex
Neurons within the primary auditory cortex are highly specialized to respond to
certain frequencies of sound
Is organized in a tonotopic fashion has a frequency-specific sensory organization
Neurons are arranged in columns
oColumns in more anterior regions of cortex respond maximally to
higher frequencies
oNeurons in posterior regions respond more to lower frequencies
Cortical neurons respond to a narrower range of frequencies than do the
neurons located earlier in the processing stream (eg. Cochlea)
Most right-handers have a right primary auditory cortex that is larger than the left
Secondary Auditory Cortex
Areas immediately adjacent to the primary auditory cortex; is located lateral and
anterior to the primary auditory cortex
www.notesolution.com

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Description
Chapter 8 [HEARING AND LANGUAGE PROCESSING] Module 8.1: The Auditory System Language production was one of the first cognitive abilities to be localized in the brain The Properties of Sound Frequency rate of vibration the number of wave cycles completed per unit of time Measured in Hertz (Hz) cycles second Human ear can perceive vibrations between 20-20,000 Hz Maximally sensitive to sounds between 1000 and 4000 Hz (human voice) Codes for pitch High frequency = high pitch Low frequency = low pitch Range of frequency that an animal perceives varies widely across species Loudness corresponds to the amplitude (intensity) of the sound wave Waves of different amplitudes differ in the degree to which the high point (condensation of air) and the low point (rarefaction of air) of the wave differ from each other Measured in decibels (dB) sound pressure of a source when compared to a standard -12 intensity of 10 watts Conversation: 40-60dB Timbre complexity of sound Fourier analysis a mathematical process in which complicated sounds are broken down into simple component waves Used to compress complex sounds on computers (MPEG-1, MP3) so that the series of simple wave forms can be efficiently represented The Ear Transduction the ear detects and amplifies very subtle vibrations and transforms these vibrations into neural signals Transduction Mechanism: Sound enters funnellike outer ear, passing through the pinna (outermost visible portion of the ear) through the hole (auditory meatus) which leads to the external ear canal External ear canal amplifies vibrations and channels them to tympanic membrane (ear drum) Tympanic membrane vibrates and passes the vibration along the three bones of the middle ear: malleus, incus, stapes Collectively, the bones are referred to as ossicles Each successive bone further amplifies the vibration, and transmits the vibration through the oval window Vibration of oval window (which is attached to the stapes) causes liquid vibrations within the cochlea (filled with cochlear fluid) www.notesolution.com Chapter 8 [HEARING AND LANGUAGE PROCESSING] Vibration of cochlear fluid causes the bending of basilar membrane and tectorial membrane elicits neural activity in hair cells Hair cells are receptor cells of auditory system; connects with vestibulocochlear nerve Anatomical Divisions of the Ear: Outer Ear pinna, external ear canal Catches and amplify sound waves Middle Ear chamber between tympanic membrane and oval window Sound waves are transduced from variations in air pressure into mechanical energy that is propagated and amplified along the ossicles to the oval window Inner Ear mechanical energy is turned into neural activity Cochlea contains inner hair cells and outer hair cells o Outer hair cells outnumber inner hair cells by 3:1 o Inner hair cells serve as receptors for auditory system; only 5% of auditory nerve cells receive inputs from outer cells o Outer hair cells modulatory role; helps to tune the cochlea through contraction and relaxation Inner Hair Cells (auditory receptors) have tiny filaments at their tips cilia that are arranged in order of height Tallest cilia kinocilium When cilia move toward direction of kinocilium: Fibers are stretched, increased firing in axons of cochlea nerve When cilia move away from kinocilium (in very quiet situations): firing in cochlear nerve falls below the normal (resting) rate Organ of Corti: Hair cells + their cilia + support cells Different parts of the cochlea respond maximally to different frequencies Basilar membrane closest to oval window is quite stiff, receptors are exposed to higher frequencies Near the helicotrema (apex), the basilar membrane is more flexible, receptors are exposed to lower frequencies Efferent projections from the cochlea demonstrate different activation under different attentional conditions Inner ear functions can be affected by higher perceptual and attentional pathways Auditory Pathways Pathway #1 1. Axons of cochlear nerve form a branch of vestibulocochlear nerve which synapses on the ipsilateral cochlear nuclei 2. Pathway A: Most projects lead to ipsilateral or contralateral superior olives Projections travel ipsilaterally to the inferior colliculus www.notesolution.com
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