Visual Perception Flashcards
Why do objects appear coloured?
Because they reflect different wavelengths of light from different parts of the visible spectrum.
What is Hue?
Hue is the quality that distinguishes red from blue.
What is brightness?
Brightness is the perceived intensity of light.
What is saturation?
Saturation characterises a colour as pale or vibrant.
What is a metamer?
A sensory stimulus that is perceptually identical to another stimulus, but physically different.
What are the 3 cone types? What colours do they associate with?
S cones - blue
M cones - green
L cones - red
What is the principle of univariance?
Any single photopigment is colour-blind because an appropriate combination of wavelength and intensity can result in an identical neural response - this is the principle of univariance.
What are dichromats?
Non-primate mammals that rely heavily on sound and smell that only have 2 pigments.
What are pentachromats?
Some birds that rely heavily on vision that have up to 5 pigments.
What type of chromat are humans? Why?
Trichromats, because we have 3 cone types.
Which type of cone do we have significantly less of than the other 2?
S cones (blue).
There are no __ cones in the fovea.
S.
Does cone distribution impact the ability to perceive colours?
No.
What is opponent coding theory?
The idea that colours are grouped into opposing pairs (blue & yellow, red & green).
___________ have chromatically opponent receptive fields. What does this mean?
Parvocellular RGCs.
This means that (for example) the centre might be excited by red light, whereas the inhibitory surround may be excited by green light.
Which layers of the LGN get their input for the achromatic luminance channel?
1 and 2.
Which layers of the LGN get their input for the two chromatic channels?
3 to 6.
What are the cardinal directions of colour space?
Red-green/cyan (0-180 hue angle) or blue/purple-yellow (90-270 hue angle). Nearly all cells at the LGN prefer stimuli modulated along this.
What is a double opponent receptive field?
Where the centre is excited by red and inhibited by green, but the surround is excited by green and inhibited by red.
What is colour constancy? What is the change in perceived colour called?
The ability to assign a fixed colour to an object, even though the actual spectral info entering the eye changes in different illumination conditions.
Chromatic induction.
What is acquired cerebral achromatopsia (CVD) typically due to damage of?
V4.
What are the % chances of colour blindness for XX and XY chromosomes in congenital CVD?
XX chromosomes: 0.5%
XY chromosomes: 8%
What types of cones does congenital CVD usually affect?
M or L cones.
What is an anomalous trichromat?
Where all 3 cone types are present, but one does not work optimally.
What do we use to detect colour vision deficiency?
Ishihara colour plates
Where does object recognition take place? What is this model called?
The two-stream model.
After the visual cortex, info is transmitted via 2 pathways.
1. The ventral stream (the what pathway)
2. The dorsal stream (the where/how pathway)
What functions is the ventral stream associated with?
Object recognition, memory.
What functions is the dorsal stream associated with?
Motion, location, saccadic control.