ProsopagnosiaAgnosia:
A failure of recognition that is not attributable to a sensory deficit or to verbal or intellectual impairment
Visual agnosia: Specific agnosia for visual stimuliCan see visual stimuli but don’t know what they areAgnosia can often be for a particular aspect of
vision (ex: color, movement, object)Prosopagnosia:
Specific visual agnosia for faces
ProsopagnosiaUsually know it is a face, but don’t know whoseSome see a jumble of facial featuresSome 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 streamSpecifically fusiform face area
Can still recognize faces, just aren’t consciously aware of it
MECHANISMS OF PERCEPTION: HEARING, TOUCH, SMELL, TASTE & ATTENTION
This chapter covers 4 of the 5 exteroceptive sensory systems
1. Auditory (hearing)2. Somatosensory (touch)3. Olfactory (smell)4. Gustatory (taste)
SENSORY SYSTEM ORGANIZATION
Like with vision, the other sensory systems are organized in a hierarchical fashion (in levels)
Primary sensory cortex Receives most of its input directly from thalamic
relay nuclei for that sense Secondary sensory cortex
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 Functional Segregation
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
Psychologists divide the general process of perceiving stimuli into 2 phases
1. Sensation Process of detecting the presence of stimuli
2. 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. Malleus (hammer)2. Incus (anvil)3. 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
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
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
AUDITORY CORTEX
2 STREAMS OF AUDITORY CORTEX
Like the visual system, there are 2 streams of audition
1. Anterior auditory pathway To prefrontal cortex Mostly involved in identifying sounds (what)
2. Posterior auditory pathway To posterior parietal cortex Involved in locating sounds (where)
DEAFNESS IN HUMANS
One of the most prevalent disabilities But total deafness is rare (only 1% of hearing-
impaired) Likely due to the network of the auditory system
2 common classes of hearing impairment1. Conductive deafness
Damage to the ossicles
2. 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 Age-related hearing loss