Chapter 4-Color and depth perception Flashcards
Color
Secondary quality that can help discriminate objects and have semantic associations
Romantic Red
Colors can elicit emotions
Wavelength and color
Close correlation between wavelength and color but light waves themselves are colorless
-620-700nm = Red
-590-620nm = Orange
-575-620nm = Yellow
-500-575nm = Green
-450-490nm = Blue
400-450nm = Violet
Visible color spectrum
We can distinguish hundreds of colors but tend to perceive colors categorically
-Primary
-Secondary
-Tertiary
Additive color mixing
Combining of reflected light waves
Subtractive Color Mixing
Mixing physical substances “cancelling” wavelengths
-Pigment combinations absorb more(subtract) wavelengths
Principle of Univariance
Infinite set of wavelength and intensity combinations can elicit the same response from a single photoreceptor
Three cones
Three cones on the retina differing in their spectral sensitivity
-S = Blue
-M = Green
-L = Red
Trichromatic Theory
Under photopic (normal illumination) conditions, all 3 cones are active
-Having three cones allows us to differentiate wavelengths/colors
-Unique pattern of activation across three cones determines what color you perceive
Why three?
Metameric matching experiment shows you need 3 cones to create metamers
-Two is not enough and more than 3 does not help
Opponent Color Theory
-After visual info leaves retina it stops in LGN
-LGN has cone (color) opponent cells with center-surround organization
(Cone signals are combined in LGN)
-Theory proposes color perception depends on the output of three color opponent neurons or channels
Chromatic Channels:
-Red/Green
-Yellow/Blue
Achromatic Channels:
-White/Black
-Perception depends on the output of these channels
-Evidence for theory:
-Illegal color combos:
-Illegal color combos are when you combine two opponent colors, you can’t see any original colors in product
-Negative Afterimages
Color vision deficiencies
Cone Dichromats (Two functioning cones)
-Deuteranopia (Missing L cones)
-Protanopia (Missing M cones)
-Tritanopia (Missing S cones)
Monochromatism (One or no cones)
-Cone monochromat (One cone)
-Rod monochromat (No cones)
Color Constancy
Surfaces tend to be the same color under a wide range of illuminants
Color Assimilation
Two different colors ‘Blend’ into each other or ‘average’ each other out
-Each color takes on some of the chromatic qualities of the other
Issues with depth perception
-World exists based on Euclidean Geometry but retinal images are Non-Euclidean
(Images are distorted and flipped)
Monocular v. Binocular depth cues
Visual cues provide info about depth
-Monocular:
Available when the world is viewed with one eye (both are ok too)
-Binocular:
-Must rely on both eyes
Monocular cue: Occlusion
Does not provide exact distance to objects just the relative ordering of objects
Monocular cue: Shading
Light comes from above, so shadowed areas suggest depth
Monocular cue: Familiar size
Familiar size of an object can aid depth perception, if the object is a known size
Monocular: Relative Size
When smaller retinal images of same object are perceived farther away
Monocular: Relative height
Relative height is based on an objects height in the visual field
Lower = closer
Higher = farther
Monocular: Ariel perspective
Light is scattered all over the place
-The farther light travels and more scattering that occurs, the bluer things appear to be
Monocular: Texture Gradient
When we see objects up close we can easily see distance between them
Monocular: Linear Perspective
When parallel lines are perceived to be parallel indefinitely
Monocular: Motion parallax
Images closer to an observer move faster across the visual field than images farther away
Binocular depth perception
Based on binocular disparity created between retinal images
-Binocular disparity:
-Difference in retinal images between the eyes produced by the same objects in visual field
Corresponding v. Non-Corresponding retinal points
Corresponding:
-Image is at the same point on each retina
E.g, Any image at the fovea
Non-corresponding:
-Image locations differ between retinas
Horopter (Vieth-mueller circle)
-Imaginary plane in the visual field that passes through an object of focus and the retina
-Objects on the horopter have corresponding retinal points
Crossed v. Uncrossed disparity
Crossed:
-Created by objects in front of the horopter
-Closer to you
Uncrossed:
-Created by objects behind the horopter
-Farther than you
Stereopsis (binocular summation)
-Combining retinal images from the two eyes
-Indicates the visual system has overcome the correspondence problem
Perceiving Size
-Visual angle is insufficient to perceive distance or size of an object because a visual angle is able to be produced with an infinite # of size/distance combos
Size Distance Scaling Function: S = R x D
-Perceived size (s) is a product of:
-Retinal Image size (R)
-Distance (D)
Size constancy
Objects of a familiar size are perceived to remain the same size
Mueller-Lyer Illusion
Perceived size illusion that may be due to misapplied depth cues
-Misapplied size scaling:
-Retinal image size is the same in both
-But Distance is perceived greater judged greater in #2
Better explained by Conflicting cues
-Perception of size is influenced by object AND surround
Ex:
<——>
>——-<
Ponzo Illusion
Misinterpretation of size induced by linear perspective
Moon Illusion
Moon appears smaller at zenith than on the horizon
-Misapplied size scaling?
-Conflicting cues(relative size)?
