Colour and perception Flashcards
Where is colour processed?
Retina
Rods = Vision at night
Cones = daylight/ colour vision
What are cells in the retina called?
cones, 3 classes that are sensitive to red, green and blue
where do cells in the retina send their info to?
They pick up different frequencies of light that are then passed to the LGN
Then areas V1, 2 and 3 construct a more detailed colour version
There are different types of color blindness deficiency depending on whether you fail to have a particular type of cone. What are 5 types?
Protanopia = no red
Protanomaly = miss tuned red
Deuteranopia = no green
Deuteranomaly = miss tuned green
Tritanopia - no blue
What are the 2 types of true colour blindness?
Cone monochromats = only one cone type
Rod monochromats = No cones at all
What are the components of Cerebral blindness (cortical colour blindness)
Patient cant see colour at all
Photoreceptors, retina, LGN, V1 all intact
Following a stroke or similar injury
Stokes affects V8 region
What is Colour opponency?
the visual system processes colours in pairs
Receptive fields processes colours in pairs
What are the two colour systems?
ancient luminance plus yellow/blue system
Newer red/green system which is a genetic adaptation
Describe colour in the visual cortex
Colour centre-surround cells in the retina normality transmit only the colour edges
These images only show edges outlined in colour
They pass through the retina to the cortex which automatically fills in the gaps with a sense of colour
What is colour constancy
your ability to see colours is consistent despite the colour of the surrounding light
Where is responsible for the conscious perception of colour
V8
What are the 3 types of cells in cortex area V1 and who proposed this?
Hubel and Wiesel (1950s)
simple cells
complex cells
hypercomplex cells
Describe the components of simple cells
orientation, position and size selective, separate off and on regions.
Length summation (strong response to long bar)
Describe the components of complex cells
orientation and size selective
prefers thin lines
no separate off and on regions
Describe the components of hypercomplex cells
like complex cells, but prefers short lines, hyper sensitive to length
How is a simple cell constructed?
combining the output from many concentric LGN
How is a complex cell constructed?
Connected to many simple cells by an OR function
How is a hypercomplex cell constructed?
3 complex cells, one with an excitatory centre with two inhibitory ends
What is texture?
The detail of an object which is finer that the actual object itself
Textures are defined by statistical properties rather than absolute values (if two textures have the same statistical properties they are the same and vice versa)
How does the brain differentiate texture?
Texton theory
Orientation contrast model
What is the Texton theory?
The physical properties that we see in the world have basic elements (texture atoms)
Therefore if two stimuli have the same number of textiles it should be difficult to differentiate
What is the Orientation contrast model ?
The brain differentiates by looking at the local contrast between one texture and another
How does the brain detect orientation?
Centre surround cells for orientation
There’s two classes of cells in V1 where there are receptive fields sensitive to the orientation stimuli
What are the two classes of cells in V1 where there are receptive fields sensitive to the orientation stimuli ?
One class = single component (orientation sensitive)
Second class = double component (orientation insensitive)
