Colour Vision & Depth Perception Flashcards
What are the three steps to colour perception?
detection, discrimination, appearence
What is involved in the detection step of colour vision?
detecting wavelengths, need photoreceptors to convert light into signals in nervous system
What is involved in the discrimination step of colour vision?
neurons that compare input from different photoreceptors, how we tell difference between wavelengths
What is involved in the appearence step of colour vision?
how wea assign perceived colours to surfaces
What wavelength do short-wavelength cones peak at?
420 nm
What wavelength do medium-wavelength cones peak at?
535 nm
What wavelength do long-wavelength cones peak at?
565 nm
What wavelenghts do rods peak at?
~500nm
What does the graph of a photoreceptors response to wavelengths look like?
roughly an arc shape with a peak in the middle, x axis is wavelengths, y axis is the response
What is the principle of univariance?
that an infinite set of combinations of different wavelenghts/intensities can cause the exact same response from a single photoreceptor
What explains the lack of colour in dimly lit scenes?
univariance
What is the solution to problem of univariance?
trichromatic solution
How does the trichromatic solution solve univariance?
using all 3 types of cones we can get a unique response for the entire range of visibile light
Explain why humans having three cones allows us to see colour at different intensities?
specific light produces a set of three responses by the 3 cones, so when intensity is changed the response size will change but the relationship between the three responses will not
What are metamers?
different mixtures of wavelengths that look identical
Does mixing wavelenghts change the physical wavelengths?
no, the mixture is only perceived
What is a additive colour mixture?
mixture of lights, all the lights are reflected off the surface to the eye, perception is the effects of the lights added together
What is a subtractive colour mixture?
if pigments A and B mix, some of the light reflected will be subtracted by A and some by B, only the remainder will affect perception
What is the neural basis of discrimination of colours?
compute the differences between cone responses
ex. L - M and (L + M) - S
What does our brain convert the three cone signals to?
L - M, (L + M) - S, L + M
What are cone opponent cells?
found in retina, LGN, and visual cortex, they subtract one cone input from another
What are some examples of cone opponent cells?
L - M, M - L, (M + L) - S, S - (L + M)
What does equilumient mean?
stimuli that vary in colour but not luminence
What is the smallest number of correctly chosen lights that can create all possible colours that humans can see?
Three
New colours generated by combining filters are? While new colours generated by mixing lights are?
Subtractive, additive
Which pigment is most important for regulating the circadian clock?
Melanopsin
What are opponent colour pairs?
a pair of colours that our brain can only recognize one at a time, they oppose one another
Whatt are some examples of opponent colour pairs?
black/white, red/green, blue/yellow
Is greenish red something that we could see according to opponent colour pair theory?
no (its an opponent pair)
What is a non spectral hue?
any colour that is not seen in the spectrum of colours made by splitting white light with a prism (anything not in rainbow)
What is achromatopsia?
inability to see colour due to damage in brain
What is colour assimilation?
how the visual system sometimes makes colours appear more similar to neighbouring colours than they actually are
What is a related colour?
a colour that can only be seen in relation to other colours
What is the image seen after the removal of a stimulus called?
afterimage
What is occlusion?
monocular cue, produced by partially overlapping objects
What is relative size?
monocular cue, judges how clsoe/far something is based on relation to other objects
What is texture gradient?
monocular cue, gradual change in appearnece of objects from coarse to fine (more to less distinct)
What is aerial perspective?
monocular cue, objects that are furhter away look bluish/blurry
What kind of information is provided by occlusion as a depth cue?
nonmetrical depth
What is nonmetrical depth describe?
provides info about the dpeth order but not depth magnitude
What is a horopter?
the surface where all points have zero disparity
What is binocular disparity?
difference in image location of an object seen by the left and right eyes
A typical depth cue depicted on a canvas by an artist is a?
pictorial depth cue
What is motion parallax?
monocular cue, objects that are closer look like they are moving faster
What is familiar size?
our knowledge of how big things are may effect our perception of their size
What is convergence?
binocular cue, how much our eyes converge to focus on an object
What is the vanishing point?
point where parallel lines seem to merge in the distnace, monocular cue
What is stereopsis?
component of depth perception gained through binocular vision
What is a common cause for stereoblindness?
strabismus
What is stereoblindness?
inability to see in 3D using stereopsis
What is strabismus?
cross eye
What is unique blue?
a hue that people see containing blue but no red or green
What is colour constancy?
the ability to perceive surface colour correctly despite changes in the colour of the illumination
What is a spectral power distribution?
a plot showing the amount of power that a light source has at each wavelength
What is a metrical depth cue?
provides quantitative information about distance in the third dimension
What are some examples of metrical depth cues?
vergence, accomodation, familiar size
What is the vieth muller circle?
an imaginary circle through the two eyes and the fixation point
What is panum’s fusional area?
the zone in which an object must appear for the two images of it in the two eyes to be fused instead of being seen diplopically
What is the first area in the visual pathway that contains binocular neurons?
V1
Give some examples of pictorial depth cues?
occlusion, texture gradient, relative height, relative size, familiar size
What is diplopia?
double vision, such as occurs when disparities are too great to be fuse
What is an unrelated colour?
a colour that can be expereienced in isolation
What is a negative afterimage?
afterimage whose polarity is the opposite of the original stimulus (red makes green after image, light makes dark, etc)
What is a spectral reflectance function?
the percentage of a particular wavelenght that is reflected from a surface
What is crossed disparity?
image falls in front of horopter, falls on left of left retina and right of right retina,
Do images appear close than the object of fixation ofr crossed disparity?
yes
