Visual system 3 Flashcards
What is the role of area V2 in visual processing?
Area V2 continues the processing of shape that begins in V1 and responds to more complex object properties such as figure/ground segregation, orientation of illusory contours, and retinal disparity.
What do cells in area V2 respond to?
Cells in V2 respond to simple properties of objects such as orientation and spatial frequency, like V1 cells. V2 also extends into crotext
which complex properties do V2 cells also respond to?
figure/ground segregation- analysis of visual scene on basis of what is object in visual scene and what is the background
orientation of illusory contours -
retinal disparity- humans have 2 eyes and because spaced horizontally- image that right eye receives will be slightly different to left eye
How is V2 organized?
V2 is organised in stripes as opposed to columns
what are the 3 types of stripes in V2
thin stripes, thick stripes and inter-stripes (also known as pale stripes)
where does V2 receive input from?
V2 receives input from both magnocellular and parvocellular cells
How does area V2 receive input from magnocellular neurons?
particularly in its thick stripes.
where does area V2 receive input from Parvocellular (PI) neurons?
interstripes
where does area V2 recieve input from Parvocellular (PB) neurons?
thin stripes
What is the primary role of area V3?
Area V3 of visual cortex is involved in processing aspects of motion, specifically, dynamic form and three-dimensional structure from motion
What is dynamic form? (V3)
neurons respond to shape information that is defined by motion differences rather than by luminance or contrast differences alone
Dynamic form helps detect what shape is present based on motion
what do V3 neurons allow us to do?
V3 neurons allow us to see shapes not just by their edges or colours but also by how different parts move (motion)
what is 3D SFM
3D SfM is the ability of the visual system to infer the three-dimensional shape of an object based on its motion, even in the absence of depth cues (lines/shading)
3D structure from motion (3D SfM) helps detect an object’s three-dimensional shape based on movement
Is Area V3 part of dorsal or ventral stream?
both
V3 is often considered part of the dorsal visual stream (associated with motion processing) but it also has connections to the ventral stream (linked to form and object recognition)
what is Area V4 known for
Area V4 is crucial for visual object recognition, with cells that respond to color and simple stimuli, as well as more complex shapes.
The precise role of V4 in visual processing is not fully understood
which area is the first area of visual cortex that is affected by changes in attention?
Area V4
it is not clear how V4 integrates feature analysis and attention processes
what do neurons in V4 respond to?
Some cells in V4 respond to relatively simple stimuli like sinusoidal frequency gratings
Other neurons in V4 respond to more complex concentric and radial stimuli (e.g. colour wheels, shapes spinning)
what impairments do monkeys with V4 lesions have?
Monkeys with V4 lesions are much more impaired on pattern recognition tasks than they are on colour tasks
Monkeys with V4 lesions can still discriminate hue but are impaired in colour constancy
which visual cortex area is concerned with processing colour constancy?
V4 is concerned with processing colour constancy
What is color constancy?
Color constancy allows objects to maintain their perceived color despite changes in lighting.
what is area V5 involved in?
involved in processing motion
what is area V5 also known as?
also known as middle temporal or MT cortex,
what do neurons ins area V5 respond to?
to an object’s position, direction of motion, and speed of motion, as well as providing depth information by responding to binocular disparity
are V5 neurons the same as V1 neurons?
V5 neurons do not differ from some neurons in V1.
V5 neurons have larger receptive fields than V1 neurons; some estimates suggest that they may be ten times larger than V1 receptive fields
How is area V5 arranged?
- in columns
- Each V5 neuron responds preferentially to a particular speed and direction of motion
how are neurons in area V5 grouped?
into direction columns, with direction preference changing systematically either clockwise or anti-clockwise as you move from one column to the next adjacent column
what takes place in the inferotemporal cortex?
Complex object recognition is thought to take place in the inferotemporal (IT) cortical area
what neurons carry out regnotion of whole objects?
Recognition of whole objects appears to be carried out by specialised neurons in inferotemporal cortex
do inferotemporal cells respond to simple or complex stimuli?
Cells in inferotemporal, or IT, cortex respond to more complex shapes that may include combinations of elements as well as motion or texture
Most IT cells do not require a natural object such as a face but require moderately complex stimuli
How do Inferotemporal neurons have such complex receptive fields?
The complex receptive fields of these IT neurons are probably a result of experience and learning
How is the inferotemporal cortex organised?
IT cortex is organised in columns
Within one column, cells are grouped according to category and similarity
All cells in the same column respond to similar but slightly different stimuli
how do cells in inferotemporal cortex respond to complex objects?
Cells in IT will respond to the features of complex objects, and these cells are grouped into columns of cells responding to similar stimulus features
what is the parietal cortex important for?
The parietal cortex is important for depth perception and motion perception
where are spatiotemporal inputs related to depth and motion integrated?
Spatiotemporal inputs related to depth and motion are integrated and interpreted in parietal cortex
what is the two streams hypothesis?
The two-streams hypothesis proposes that the human visual system processes information through two distinct pathways: a dorsal stream for spatial processing and action guidance, and a ventral stream for object recognition and identification.
The two-streams hypothesis proposes two main pathways in the brain: the ventral “what” pathway for object identification and the dorsal “where” pathway for motion and spatial processing.
where does the ventral pathway start and end?
starts in occipital cortex and ends in temporal cortex
which neurons does the ventral pathway receive input from
parvocellular neurons
which brain areas contribute to the ventral pathway?
V1
V2
V4
inferotemporal cortex
where does the dorsal pathways start and end?
starts in occipital cortex and ends in parietal cortex
which neurons does the dorsal pathway receive input from?
magnocellular neurons
which brain areas contribute to the dorsal pathway
V1
V2
V3
V5
parietal cortex
What happens if area V5 is damaged?
Akinetopsia is a severe impairment in the perception of motion resulting from bilateral damage to V5 (dorsal)
Shapes, objects and faces can be identified without difficulty; however, the perception of motion is severely impaired
Motion is perceived as abrupt and jerky with sudden changes in the position of an object rather than the smooth perception of an object in motion
does damage to V5 abolish all motion perception?
no, Damage to V5 does not abolish all motion perception because other cortical areas such as area V3 are also involved in the processing of motion
what can Bilateral damage to the temporal lobes (ventral pathway) result in?
a deficit in object recognition known as visual agnosia
Vision, language, memory and intelligence remain intact
There are no problems with `seeing’ or understanding or communicating
Problem is with the integration and interpretation of visual input in the ventral pathway (seeing without recognising)
How does DF’s case study support the separation of the ventral and dorsal streams?
DF showed impairment in perceptual tasks but normal motor (visuospatial) tasks, suggesting separate ventral and dorsal streams. However, later studies found overlap in these pathways.
What is the “vision-for-action” vs “vision-for-perception” approach?
This approach suggests that the dorsal pathway is for guiding actions (vision-for-action), while the ventral pathway is for object identification and visual perception (vision-for-perception).
