Prosopagnosia
 Agnosia:
 A failure of recognition that is not attributable to a
sensory deficit or to verbal or intellectual impairment
 Visual agnosia:
 Specific agnosia for visual stimuli
 Can see visual stimuli but don’t know what they are
 Agnosia can often be for a particular aspect of vision (ex:
color, movement, object)
 Prosopagnosia:
 Specific visual agnosia for faces
Prosopagnosia
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Usually know it is a face, but don’t know whose
Some see a jumble of facial features
Some can’t recognize themselves!
Some evidence suggests that this is really an inability
to identify individual items from a group; not just
faces
 Often associated with damage to ventral stream
 Specifically fusiform face area
 Can still recognize faces, just aren’t consciously aware
of it
MECHANISMS OF PERCEPTION:
HEARING, TOUCH, SMELL,
TASTE & ATTENTION

1.
2.
3.
4.
This chapter covers 4 of the 5 exteroceptive
sensory systems
Auditory (hearing)
Somatosensory (touch)
Olfactory (smell)
Gustatory (taste)
SENSORY SYSTEM ORGANIZATION
Like with vision, the other sensory systems are
organized in a hierarchical fashion (in levels)
 Primary sensory cortex
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Secondary sensory cortex
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Receives most of its input directly from thalamic
relay nuclei for that sense
Input from primary & other areas of 2ndary for that
sense
Association cortex

Any area of cortex that gets info from more than one
sensory system; usual from 2ndary
SENSORY SYSTEM ORGANIZATION

Hierarchical Organization
As you go up levels, the neurons respond to stimuli of
greater specificity and complexity
 Adds another layer of analysis as it to a new level
 The higher the level of damage in the system, the more
specific & complex the sensory deficit
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Functional Segregation
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Each level of the cortex in each sensory system contains
functionally distinct areas that specialize in different kinds
of analysis
Parallel Processing

Info in sensory systems flows through multiple pathways &
undergo simultaneous analysis in different ways along
these different paths (not a serial system)

The brain transmits sensory information to/from
multiple places at multiple levels in multiple directions
from multiple senses & integrates it all together!
SENSORY SYSTEM DIVISION

1.
Psychologists divide the general process of
perceiving stimuli into 2 phases
Sensation

2.
Process of detecting the presence of stimuli
Perception

Higher-order process of integrating, recognizing &
interpreting complete patterns of sensations
AUDITORY SYSTEM
Function: perception of sound
 Sounds: vibrations of air molecules that
stimulate the auditory system; come in waves
 Human hearing is within the 20-20,000Htz range

THE EAR & SOUND
Sound waves are caught & funneled into the ear
by the pinna
 Sound travels from the outer ear down the
auditory canal & causes the tympanic
membrane (eardrum) to vibrate
 The vibrations are then transferred to the 3
ossicles (tiny bones of the middle ear)

1.
2.
3.
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)

Vibrations of the stapes cause the oval window
membrane to vibrate, which sends the vibrations to
the fluid in the cochlea

The cochlea is a long coiled tube with a membrane (the
organ of Corti) running along it

This is the official auditory receptor organ
Each pressure change at the oval window sends a
wave down the organ of Corti, which shifts its 2
membranes: basilar & tectorial
 These membranes are covered in hair cells (auditory
receptors) & when they bend due to the shift in
membrane, they fire APs within the auditory nerve
 The vibrations ultimately are dissipated by the round
window
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VESTIBULAR SYSTEM
The vestibular system is responsible for
dealing with information regarding the direction
& intensity of head movements; essentially
balance & staying upright
 The receptive organs of this system are the
semiciruclar canals

EAR TO PRIMARY AUDITORY CORTEX
No major pathway, but a network of pathways
 Each auditory nerve synapses in the ipsilateral
cochlear nuclei, then to the superior olives on
both sides, to inferior colliculi, to medial
geniculate nuclei (MGN of thalamus) to
primary auditory cortex
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SUBCORTICAL MECHANISMS OF SOUND
LOCALIZATION
You determine the location of sound based on the
fact that a sound will reach one ear slightly
earlier and louder than the other
 Neurons in the medial superior olive responds to
the different timing
 Neurons in the lateral superior olives respond to
the different amplitude
 The olives send the signal to the superior
colliculus, which maps out the location of the
sound
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AUDITORY CORTEX
2 STREAMS OF AUDITORY CORTEX

1.
Like the visual system, there are 2 streams of
audition
Anterior auditory pathway
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2.
To prefrontal cortex
Mostly involved in identifying sounds (what)
Posterior auditory pathway
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To posterior parietal cortex
Involved in locating sounds (where)
DEAFNESS IN HUMANS
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One of the most prevalent disabilities

But total deafness is rare (only 1% of hearingimpaired)

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1.
2 common classes of hearing impairment
Conductive deafness
Damage to the ossicles

2.
Likely due to the network of the auditory system
Nerve deafness
Damage to the cochlea or auditory nerve
Most common cause is loss of hair cells
Partial damage to cochlea results in deafness for
only some frequencies
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Age-related hearing loss