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