Slide 3 Flashcards
What is contrast enhancement?
- mechanism in visual system
- enhances perception of brightness contrast
- between 2 areas
What is an example of contrast enhancement
mach bands
What is the neural basis to contrast enhancement?
lateral inhibition
Define lateral inhibition
- enhancing the effect of a cell
- by inhibiting
- neighbouring cells
During the process of lateral inhibition, what results in a higher firing rate?
more intense light
During the process of lateral inhibition, what cells are inhibited the most?
closest neighbours
What cells are responsible for lateral inhibition in the mammalian retina?
horizontal cells
What is the component (trichromatic) theory?
What are the 3 types of cones?
- short
- medium
- long
What is the opponent process theory?
- 3 sets of cells
- that perceive colour
- in opposing pairs
- if one colour is activated its opponent is inhibited
Name 3 opposing pairs that exemplify the opponent process theory
- red/green
- black/white
- blue/yellow
Evidence for the opponent process theory
complimentary afterimage
What levels of the visual system does the opponent process theory occur at?
- all levels
- beyond receptors
What is an example of the ability of sensory systems to adapt in the opponent process theory?
- adaptation of red receptors
- results in less inhibition of green receptors
What is colour constancy and which of the two theories can explain it (opponent process/component)
- tendency of an object to be perceived as the same colour
- despite large changes
- in the wavelength of light it reflects
Who is responsible for the retinex theory?
Edwin Land
What is the retinex theory?
- perception of colour
- is determined by its reflectance
- relative wavelengths are constant
- so perception is constant
What is reflectance
- proportion of light of diff wavelengths
- which a surface reflects
which areas go beyond the primary visual cortex
- secondary areas
- association areas
There are more than __ visual fields found
30
What are extrastriate areas and how are they identified?
- areas beyond the striate cortex
- V2, V3, V4 etc
- larger receptive fields
- more specialized in function
What is the dorsal stream?
- where pathway
- V1 -> V2 -> posterior parietal cortex
What is the function of the dorsal stream
determining the location of objects in space
What is the ventral stream?
- what pathway
- V1 -> V2 -> inferior temporal cortex
