1. Copyright © 2009 Allyn & Bacon
Chapter 7: Mechanisms of
Perception – Hearing, Touch,
Smell, Taste, and Attention
How You Know the World
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2. The Case of the Man Who Could See Only One Thing at a Time
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?
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3. Principles of Sensory System Organization
Primary – input mainly from thalamic relay nuclei
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
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4. Principles of Sensory System Organization (continued)
Hierarchical organization
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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5. Copyright © 2009 Allyn & Bacon
Two models of sensory system organization
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6. Copyright © 2009 Allyn & Bacon
Auditory System: Sound The relation between the physical and perceptual dimensions of sound
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7. Copyright © 2009 Allyn & Bacon
The Ear
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
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8. Copyright © 2009 Allyn & Bacon
The Ear (continued)
Semicircular canals
Auditory
Nerve
Cochlea
(unwound)
Round
window
Oval window
Tympanic
membrane
Tectorial
membrane
Hair cells
Organ
of Corti
Basilar
membrane
Anatomy of the ear
Auditory
nerve
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9. Copyright © 2009 Allyn & Bacon
The Ear (continued)
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
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10. Copyright © 2009 Allyn & Bacon
The Ear (continued)
Organ of Corti
Composed of two membranes
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
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11. Copyright © 2009 Allyn & Bacon
The Ear (continued)
Cochlear Coding
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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12. The Ear (continued) Some pathways of
the auditory system from one ear to
the cortex
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13. Subcortical Mechanisms of Sound Localization
The lateral and medial superior olives react to differences in what is heard by the two ears
Medial – arrival time differences
Lateral – amplitude differences
Both project to the superior colliculus
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
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14. Primary and Secondary Auditory Cortex
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 well-researched
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15. Effects of Damage to the Auditory System
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
Total deafness is rare, due to multiple pathways
Two kinds: conductive deafness (damage to ossicles) and nerve deafness (damage to cochlea)
Partial cochlear damage results in loss of hearing at particular frequencies
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16. Somatosensation: Touch and Pain`
Somatosensory system is three separate and interacting systems:
Exteroceptive – external stimuli
Proprioceptive – body position
Interoceptive – body conditions (e.g., temperature and blood pressure)
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17. Somatosensation: Touch and Pain (continued)
Exteroceptive System
Touch (mechanical stimuli)
Temperature (thermal stimuli)
Pain (nociceptive stimuli)
Specialized receptors respond to the various stimuli
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18. Somatosensation: Touch and Pain (continued)
Cutaneous Receptors
Free nerve ending
temperature and pain
Pacinian corpuscles
adapt rapidly, large and deep; onion-like
sudden displacements of the skin
Merkel’s disks – gradual skin indentation
Ruffini endings – gradual skin stretch
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19. Touch and Pain (continued)
Four cutaneous
receptors that occur
in the human skin
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Figure Cutaneous receptors

20. Somatosensation: Touch and Pain (continued)
Cutaneous Receptors
We respond to change – when there is no change, no sensation
Stereognosis – identifying objects by touch
Dermatome – the area of the body innervated by the left and right dorsal roots of a given segment of spinal cord
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21. Two Major Somatosensory Pathways
Dorsal-column medial-lemniscus system
Mainly touch and proprioception
First synapse in the dorsal column nuclei of the medulla
Anterolateral system
Mainly pain and temperature
Synapse upon entering the spinal cord
Three tracts – spinothalamic, spinoreticular, spinotectal
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22. medial-lemniscus system Antero-lateral system
Dorsal-column
medial-lemniscus system
Antero-lateral system
Two
Major
Somato-
sensory
Path-
ways
(continued)
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Figure 7.12 , p.173