Download exteroreceptive sensory systems

Chapter 7: Mechanisms of
Perception – Hearing, Touch,
Smell, Taste, and Attention
How You Know the World
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Copyright © 2009 Allyn & Bacon
The Case of the Man Who Could
See Only One Thing at a Time
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This chapter focuses on the four
exteroreceptive sensory systems besides
vision that interpret external stimuli
Why would a man be unable to see two
objects simultaneously when he can see
each individually?
What could cause this deficit?
Copyright © 2009 Allyn & Bacon
Principles of Sensory System
Organization
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Primary – input mainly from thalamic relay nuclei
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For example, striate cortex receives input from
the lateral geniculate nucleus
Secondary – input mainly from primary and
secondary cortex within the sensory system
Association – input from more than one sensory
system, usually from secondary sensory cortex
Copyright © 2009 Allyn & Bacon
Principles of Sensory System
Organization (continued)
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Hierarchical organization
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Specificity and complexity increases with each
level
Sensation – detecting a stimulus
Perception – understanding the stimulus
Functional segregation – distinct functional
areas within a level
Parallel processing – simultaneous analysis of
signals along different pathways
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Two models of sensory system organization
Copyright © 2009 Allyn & Bacon
Auditory System: Sound
The relation between the physical and perceptual dimensions of sound
Copyright © 2009 Allyn & Bacon
The Ear
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Sound waves enter the auditory canal of
the ear and then cause the tympanic
membrane (the eardrum) to vibrate
This sets in motion the bones of the
middle ear, the ossicles, which trigger
vibrations of the oval window
Copyright © 2009 Allyn & Bacon
The Ear (continued)
Semicircular canals
Auditory
Nerve
Cochlea
(unwound)
Round
window
Oval window
Tympanic
membrane
Tectorial
membrane
Hair
cells
Anatomy of the ear
Auditory
nerve
Copyright © 2009 Allyn & Bacon
Basilar
membrane
Organ
of Corti
The Ear (continued)
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Sound wave > eardrum > ossicles (hammer,
anvil, stirrup) > oval window
Vibration of the oval window sets in motion
the fluid of the cochlea
The cochlea’s internal membrane, the organ
of Corti, is the auditory receptor organ
Copyright © 2009 Allyn & Bacon
The Ear (continued)
Organ of Corti
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Composed of two membranes
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Basilar membrane – auditory receptors,
hair cells, are mounted here
Tectorial membrane – rests on the hair
cells
Stimulation of hair cells triggers action
potentials in the auditory nerve
Copyright © 2009 Allyn & Bacon
The Ear (continued)
Cochlear Coding
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Different frequencies produce maximal
stimulation of hair cells at different
points along the basilar membrane
Tonotopic (frequency) organization of
the basilar membrane and most other
auditory system components
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The Ear
(continued)
Some pathways of
the auditory system
from one ear to
the cortex
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Subcortical Mechanisms of
Sound Localization
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The lateral and medial superior olives
react to differences in what is heard by
the two ears
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Medial – arrival time differences
Lateral – amplitude differences
Both project to the superior colliculus
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The deep layers of the superior colliculus is laid
out according to auditory space, allowing location
of sound sources in the world; the shallow layers
are laid out retinotopically
Copyright © 2009 Allyn & Bacon
Primary and Secondary
Auditory Cortex
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Two or three areas of primary auditory
cortex
About seven areas of secondary auditory
cortex
Functional columns (cells of a column
respond to the same frequency)
Tonotopic organization
Secondary areas do not respond well to
pure tones and have not been wellresearched
Copyright © 2009 Allyn & Bacon
Effects of Damage to the
Auditory System
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Lesions of auditory cortex in rats results in few
permanent hearing deficits
Lesions in monkeys and humans hinder
sound localization and pitch discrimination
Deafness in humans
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Total deafness is rare, due to multiple pathways
Two kinds: conductive deafness (damage to
ossicles) and nerve deafness (damage to cochlea)
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Partial cochlear damage results in loss of hearing at
particular frequencies
Copyright © 2009 Allyn & Bacon