Visual System V Flashcards
Which cortex is referred to as the “face center”
Inferotemporal cortex
Neurons in the ventral stream exhibit properties that are important for object recognition. At the highest levels in this pathway, visual neruons in the monkey inferior temporal cortex respond preferentially to the presentation of faces.
Describe the columnar organization in extrastriate cortex.
V1, MT and IT
V1: orientation/ocular dominance columns
MT: directions of motions columns. (stimulus has to be moving in a specific direction for these neurons to be active)
IT (inferotemporal cortex): columns response to categories of shapes. (interested in different kinds of object stimuli)
all have overlapping receptive fields
If you had a lesion to dorsal pathway or ventral pathway, what would be the difference?
Dorsal stream - magno input - towards parietal cortex - action pathway
- therefore lesion would result in a lot of difficulty in using vision to guide action
Ventral stream - parvo input - toward inferotemporal cortex - perception pathway
- therefore lesion would result in difficulties with visual perception. eg cant really describe something from visual stimuli (impaired perception) BUT can properly outgo actions.
- eg if asked about orientation of a movement (perceptual) unable to recall but able to perfectly replicate motor actions
What does attention allow for, and what are the two ways it can be controlled,?
Attention allows us to select specific images or features, while ignoring others.
Attention can be controlled voluntarily as well as automatically/reflexively.
automatic/reflexive: Bottom-up (stimulus driven, exogenous) control.
Voluntary: top-down (goal oriented, endogenous).
What is bottom up control? What are the critical structures involved?
- stimulus driven, exogenous control
- driven by unexpected exogenous sensory stimuli
- bottom-up attention happens automatically when novel salient stimuli appear
- critical structures include superior colliculus, thalamus, V1, temporoparietal junction (TPJ), ventral frontal cortex (VFC)
when something new happens in the environment that captures your attention. eg door blowing up in lecture
What is top-down control? What are the critical structures involved?
- goal oriented, endogenous control
- under full voluntary control
- requires no stimuli at all (you can imagine the presence of relevant stimuli or locations)
- critical structures include the fronto-parietal cortical network (front eye fields (FEF), intraparietal sulcus (IPS), superior colliculus (SC))
doug saying “i want you to pay attention to the door” and we voluntarily shift our attention there. Under endogenous control, doesnt require any stimulus
Where is attention control localized in the brain?
localized on the right side of the brain, part of the dorsal stream (right fronto-parietal hemisphere)
Most people that are right handed, speech and visual skills are focused in the ________ hemisphere of the brain (_______ area)
Most people that are right handed, speech and visual skills are focused in the LEFT hemisphere of the brain (BROCAS area)
A right parietal lesion can produce what in terms of attention control?
RIGHT parietal lesion can produce NEGLECT.
this means there is no attention on the left, so if something is happening on the left it WONT capture attention. The patient can still deploy attention to the right side, but completely ignore left.
which is more severe, neglect or exctintion? Which results from which lesion?
NEGLECT more severe than extinction.
Neglect results from lesion to the right hemisphere
Extinction results from lesion to the left hemisphere.
What lesion would a patient probably have if they ate all the food on the right side of the plate but not the left side of the plate?
A right parietal lesion, producing neglect.
T or F: At the highest level in the dorsal pathway, visual neurons in the monkey parietal cortex are selectively activated by stimuli that are behaviourally relevant. Explain why true or false.
True.
- eg, for an action
- when your attention system is looking for something
- very important for filtering out useless visual info
- eg doug standing in front of the classroom, looking at us, the bricks on the wall behind him with all different orientations of lines is ignored because he is paying attention to our faces.
Which one is top-down and which one is bottom-up?
Ventral vs dorsal pathways
Dorsal attention system (top-down)
Ventral attention system (bottom-up)
