Primary Visual Cortex and Beyond Flashcards
What does contrast sensitivity vary with?
Spatial frequency
Which retinogeniculate pathway would be required to resolve the highest spatial frequencies?
Parvocellular pathway
Which retinogeniculate pathway would be required to resolve the highest temporal frequencies?
Magnocellular pathway
What is the modulat hypothesis of visual function?
- Functional specialisation of the visual cortex
- Parallel nd separate processing of the image attributes in the different cortical areas (colour, form, motion)
Outline the pathway of magnocellualr cells
- The projections from V1 LGN go to the thick stripe of V2
- Then there are projections to the dorsal MT (V5) to process motion
Outline the pathway fo parvocellular cells
- The projections from V1 LGN go to the thin stripe of V2
- Then there are projections to the ventral V4 to process colour
What do the dorsal and ventral streams detect?
Dorsal - spatial
Ventral - object recognition
What has been used as evidence to support functional specialisation?
- lesion studies
- neuropsychological assessments following focal brain damage in humans
- electrophysiology
- imaging
What are the properties of neurons in the inferotemporal cortex?
- Large RFs extending across the midline usually including the fovea
- Response invariant - retinal size and precise position within the RF doesn’t affect response
- Many cells are ‘face’ cells but other patterns can be effective and may be modifiable with training and attention
What is the neuron doctrine?
- Idea that neural responses become increasingly selective at higher stages in neural pathways
- Specific elements of our perceptions are caused by activation of specific populations of neurons, selective for those elements
- Termed as either cardinal or grandmother cells
- Implies population size must decrease as selectivity increases, sparse coding
What is the function of motion in the visual stimulus?
- Helps figure out ground segregation
- Draws attention
- Location and navigation
How is motion detected?
- Detectors with delay line
- Illusions of visual motion also suggestive of specialised motion processing subsystem
What is the modular hypothesis of visual function?
- Functional specialisation of the visual cortex
- Parallel and separate processing of image attributes in different cortical areas (colour, form, motion)
How is motion processed?
- receives input from M pathway via V1 & V2
- Retinotopically mapped
- Cells sensitive to direction and speed of motion
- Columnar organisation
Global v Elemental Visual Motion
- some V1 cells are sensitive to moving oriented edge
- Consider aperture problem
