Lecture 7: Visual Processing Streams and Agnosia

Weeks 4-7

dorsal stream (who/what/when/where/why/how)

where/how

where is the dorsal stream associated with

inferior parietal lobe

ventral stream (who/what/when/where/why/how)

who/what

where is the ventral stream associated with

inferior temporal lobe

dorsal stream functions

spatial location

dorsal stream functions

topographical orientation

dorsal stream functions

planning and coordination of movement

deficits in the dorsal stream lead to

hemispatial neglect

what is hemispatial neglect

attentional problem (visual fields are fine) where the brain doesn’t pay attention to one side (L or R) of space

most common type of hemispatial neglect and due to what

left neglect due to a RH lesion

deficits in the dorsal stream lead to

apraxia

what is apraxia

difficulty planning movement despite having the ability to do so

types of apraxia

limb-kinetic, ideomotor, conceptual

limb-kinetic apraxia

difficulty with fine motor coordination (clumsy)

ideomotor apraxia

difficulty connecting the idea of the movement to the actual movement; can still spontaneously do the behavior

conceptual apraxia

lost knowledge of the behavior

deficits in the dorsal stream lead to

left-right discrimination problems

ventral stream functions

object recognition

ventral stream functions

matching visual shape/color to internal representations

deficits in the ventral stream lead to

visual agnosia

what is visual agnosia

inability to recognize/name objects

fusiform face area (FFA) function

recognizing faces and other familiar visual stimuli (ex: bird watcher recognizing birds)

agnosia

failure to recognize previously familiar stimuli (can be visual, touch, auditory, smell, etc)

what does it mean for agnosia to be modality-specific

you still conceptually know what an object/sound/taste/etc is, you just cannot recognize it

agnosia and classes of stimuli

agnosia can be limited to certain classes of stimuli

• manmade objects vs natural objects

• person standing vs person running

prosopagnosia

inability to recognize familiar faces

most common cause (where is the lesion) of prosopagnosia

RH

auditory sound agnosia

inability to recognize sounds of common objects

phonagnosia

inability to recognize familiar people by their voices

tactile agnosia

inability to recognize what is placed in one hand

astereognosis

inability to recognize what is placed in both hands (bilateral)

simultanagnosia

inability to recognize more than one object at a time

one of the two overarching types of agnosia

apperceptive agnosia

one of the two overarching types of agnosia

associative agnosia

what is apperceptive agnosia

inability to recognize or name objects

copying objects with apperceptive agnosia

cannot copy unrecognized objects

what is apperceptive agnosia evidence of

sensory-perceptual disturbances can explain the deficit

what is associative agnosia

inability to recognize or name objects

copying objects with associative agnosia

can copy unrecognized objects

what is associative agnosia evidence of

sensory-perceptual disturbances cannot explain the deficit

primary way to differentiate between apperceptive and associative agnosia

copy method

which stream is agnosia associated with

ventral stream

what is sensory-perceptual impairment

perceptions of the object are fuzzy

explanations for agnosia

any impairment in the object → memory → language tract

which type of prosopagnosia is more severe (apperceptive or associative)

apperceptive

where is vision dominant

RH

where is verbal dominant

LH

which hemisphere is a lesion more commonly found with prosopagnosia

RH

specifically where in the hemisphere is a lesion more commonly found with prosopagnosia

temporal lobe

bilateral occipitotemporal lesion in prosopagnosia

extent of damage determines the presence of an apperceptive defect (because apperceptive is more severe, and bilateral is both hemispheres)

tests for dorsal stream deficits

clock drawing

tests for dorsal stream deficits

matching line orientation

tests for dorsal stream deficits

replicate the pattern with blocks