Visual System Part 3 Flashcards
V2 Prestriate cortex
receives visual information from V1
receptive fields are larger than V1
receptive fields are now binocular
receptive fields begin to show contextual effects
cells respond to imaginary lines
neurons show different firing if objects is in foreground or background
Where does V2 send information
dorsal or ventral stream
Dorsal stream
path that identifies location and direction of objects
also provides identification of certain types of movements
Dorsal V3
receives information from V2 and V1
responds to large movements
very large receptive fields
first stage in processing changes in visual stimuli when you move
MST/MT/V5
cortical center for perception of movement
neurons in this area integrate information from ground/figure movement, head movement, and line/object movement
Area MT: Dorsal
global changes in visual motion
compensates for body’s movement in the environment
Optic Flow
as we move around, entire scene shifts, magnifies around us
Area MT: Ventral
identifies objects in motion responds to motion responds to images that depict motion Cells in MT can be selective to accelerate, direction, speed
Simultagnosia
Difficult in perceiving multiple items
Ventral simultagnosia
Can only be aware of one ‘thing’ at a time
Dorsal simultagnosia
Can be aware of multiple objects but can only identify one at a time
Hemispatial neglect
patients appear to neglect half their visual field
Akinetopsia
an inability to perceive motion
vision is replaced by frozen images
Ventral stream
identifies contents of visual field
important for object, identification, colour, and form
Ventral V3
receives information from V1/V2
passes information on to V4
Ventral V4
encodes more complicated visual information
colour, and simple shapes make neuron fire
helps keep colour information consistent in the brain
neurons fire faster when stimulus is being attended to
Globs
areas of V4 that are sensitive to colour
Colour Constancy
mechanism that allows us to see colour in a similar way even in different lighting situations and distances
How do we see 3D
the mind creates an illusion using shading, lines, patterns, and contours
integrates information from both dorsal and ventral stream
Final output is in the inferotemporal Cortex which is activated by 3D shapes
What is the 3-D model of recognition
inside our brain is a 3D model of the object which we match to what we are perceiving
Recognition of components
objects are brown down into simple geometric shapes which can be combined to form shapes
Viewpoint dependent
specific orientation of object is stored, and there are many memories of the same object
Multiple Views
mix of all the other theories
suggests components/3D model for general objects, but viewpoint dependence for specific things
Lateral Orbital Cortex
recognizes objects
neurons fire when they recognize a texture but fire the most when they recognize an object
Parahippocampal place area
activated when viewing landscapes, cityscapes, houses, or rooms
Fusiform face area
activated when shown faces, cartoon faces, drawing of faces
Theory for FFA function
because of face’s importance, we evolved an area specialized for faces
because of face’s importance, we evolved an area specialized for differentiating between very similar things
Prosopagnosia
after damage to the face, they are unable to recognize faces
Blindsight
patients are perceptually bind, report no vision
blindness is typically from V1 damage
when forced to choose, will show better than chance performance on a variety of tasks
will sometimes ‘dodge’ objects while moving
How can patients with blindsight dodge objects?
LGN sends some projections directly to extrastriate areas of visual cortex
these limited projections aren’t enough to allow subjects to perceive vision, but can subtly influence rest of cortex
