Prosopagnosia

1. 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

2. Prosopagnosia • 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

3. Mechanisms of Perception: Hearing, Touch, Smell, Taste & Attention

4. This chapter covers 4 of the 5 exteroceptive sensory systems • Auditory (hearing) • Somatosensory (touch) • Olfactory (smell) • Gustatory (taste)

5. 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

6. 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)

7. The brain transmits sensory information to/from multiple places at multiple levels in multiple directions from multiple senses & integrates it all together!

8. Sensory System Division • Psychologists divide the general process of perceiving stimuli into 2 phases • Sensation • Process of detecting the presence of stimuli • Perception • Higher-order process of integrating, recognizing & interpreting complete patterns of sensations

9. 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

10. 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) • Malleus (hammer) • Incus (anvil) • Stapes (stirrup)

12. 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

14. 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

15. Ear to Primary Auditory Cortex • No major pathway, but a network of pathways • Each auditory nerve synapses in the ipsilateralcochlear nuclei, then to the superior olives on both sides, to inferior colliculi, to medial geniculate nuclei (MGN of thalamus) to primary auditory cortex

16. 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

17. Auditory Cortex

18. 2 Streams of Auditory Cortex • Like the visual system, there are 2 streams of audition • Anterior auditory pathway • To prefrontal cortex • Mostly involved in identifying sounds (what) • Posterior auditory pathway • To posterior parietal cortex • Involved in locating sounds (where)

19. 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 impairment • Conductive deafness • Damage to the ossicles • 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