Perception of Colour and Motion Flashcards
In what layer of the cortex (V1) do M cells terminate?
4Ca
In what layer of the cortex (V1) do P cells terminate?
4Cb
What are the other 3 main outputs from V1 and the associated layers?
Layer 3 and 4B: to other (extrastriate) cortical areas
Layer 5: superior colliculus and pons
Layer 6: LGN
What is the cellular pathway involved in detection of motion?
M ganglion cells project to magnocellular layers of LGN
M cells from LGN project to layer 4Ca of V1
Cells in layer 4Ca project to layer 4B
When does mixing of ipsilateral and contralateral visual information occur?
After input into V1
Describe the concept of “directional selectivity”. Where are neurons displaying directional selectivity found?
Some neurons show preference for the direction of motion of the target
In layer 4B, area MT
What % of the cortex is involved in vision?
40%
What are the 2 cortical streams of visual processing and what is each responsible for?
Dorsal pathway: where in the visual field an object is
Ventral pathway: what the object is (shape and colour)
What is area MT and what is its role? Which stream is it associated with (ventral or dorsal)
Middle temporal lobe, associated with dorsal stream
For processing object motion
From what cortical areas does area MT receive inputs?
V1 (specifically cells in layer 4B), V2, V3
How is white observed?
Via red, green and blue light causing equal activation of the 3 types of cones
What is a colour opponent centre surround?
Phenomenon exhibited by some P ganglion cells in which they are excited by 1 colour falling on their centre and inhibited by another falling on their surround
What pairs of colours are compared (e.g. in colour opponent centre surround)?
Green vs. red
Blue vs. yellow
What is area V4 and what is its role? Is it associated with the dorsal or ventral stream?
Associated with ventral stream
Important for perception of shape and colour (object recognition)
From what cortical areas does area V4 receive inputs?
Blob and interblob regions of V1, via V2
Are neurons in area V4 directionally selective?
They are both directionally selective and colour selective
Where is area V4’s major output to?
Area IT (inferior temporal)
What do neurons in area IT respond to? What is the major role of area IT?
Neurons respond to a wide variety of abstract shapes and colours
Important for visual memory and perception (especially of faces)
What are the 3 groups of colour blindness?
Monochromacy
Dichromacy
Anomalous trichromacy
What is monochromacy?
Individuals have only 1 type of cone
What is dichromacy?
Individuals have only 2 functional cones
What is anomalous trichromacy?
Individuals have all 3 cones, but 1 expresses abnormal pigment and doesn’t work as well as normal cones
What are the 3 different type of inherited colour vision deficiency?
Protan
Deutan
Tritan
Are M cells wavelength sensitive or insensitive?
Insensitive (do not detect colour)
What is the relative frequency of rate of AP firing in R+G- ganglion cells when stimulated a) with R just at the ON centre, b) with R at the ON centre and at the OFF surround, and c) with R at the ON centre and G at the OFF surround? Give some explanation if required
a) Maximal excitation
b) Less excitation than in a) (green cones are excited by red light and so provide some inhibitory input, but not as much as would be produced by green light)
c) Maximal inhibition (low output - similar to no light)
What is a protanope vs. a protanomal?
Protanope: no red cones
Protanomal: abnormal red cones
What is a deutanope vs. a deutanomal?
Deutanope: no green cones
Deutanomal: abnormal green cones
What is a tritanope vs. a tritanomal?
Tritanope: no blue cones
Tritanomal: abnormal blue cones
What are some of the everyday deficits experienced by protanopes?
Fail to see red lights and signals as easily, and require larger stopping distances when driving
What are some of the everyday deficits experienced by deutanopes?
Can confuse red and yellow traffic lights
