Trichromacy

•      The theory that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptor types now known to be the three cones

§  Also known as the Young–Helmholtz theory

•      Different mixtures of wavelengths that look identical. More generally, any pair of stimuli that are perceived as identical in spite of physical differences.  Because of relative firing pattern. These are the muted washed out colors, because  there is less contrast and amplitude.  

•      has cells that are maximally stimulated by spots of light

§  Visual pathway stops in ____ on the way from retina to visual cortex

§  cells have receptive fields with center–surround organization

•      A neuron whose output is based on a difference between sets of cones

q  The distance from black in color space

•       theory that perception of color is based on the output of three mechanisms, each of them based on an opponency between two colors: Red–green, blue–yellow, and black–white. See-saw effect. We have gray, which is mix of black and white, but we don’t have anything like that for the other main colors.

•      noticed that some color combinations are legal while others are illegal

§  We can have bluish green, reddish yellow (orange), or bluish red (purple)

§  We cannot have reddish green or bluish yellow.

§  Because if they are perceived oppositely through the on center off surround method then you can’t see them both together because both can’t fire.

§  Any of four colors that can be described with only a single color term: Red, yellow, green, blue

§  For instance, unique blue is a blue that has no red or green tint

§  Step 1: Detection. S, M, and L cones detect light

§  Step 2: Discrimination. Cone opponent mechanisms discriminate wavelengths

q  [L – M] and [M – L] compute red vs. green. Subtract off center and on center

q  [L + M] – S and S – [L + M] compute blue vs. yellow. Subtract out short wavelengths.

§  Step 3: Appearance. Further recombination of the signals creates final color-opponent appearance

§  Further filling in of information of hue, saturation, brightness, etc

•      An afterimage whose polarity is the opposite of the original stimulus

§  Have no cones of any type; truly color-blind and badly visually impaired in bright light

•      : A color perception effect in which the color of one region induces the opponent color in a neighboring region

•      A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other

•      A color, such as brown or gray, that is seen only in relation to other colors

§  A “gray” patch in complete darkness appears white

•      The tendency of a surface to appear the same color under a fairly wide range of illuminants

§  To achieve color constancy, we must discount the illuminant and determine what the true color of a surface is regardless of how it appears

•      Parallel lines remain parallel as they are extended in space

§  Objects maintain the same size and shape as they move around in space

§  Internal angles of a triangle always add up to 180 degrees, etc.

•      Notice that images projected onto the retina are non-Euclidean!

•      The combination (or “summation”) of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone

The two retinal images of a three-dimensional world are not the same

•      The differences between the two retinal images of the same scene

§  basis for stereopsis, a vivid perception of the three-dimensionality of the world that is not available with monocular vision

•      A depth cue that provides quantitative information about distance in the third dimension

•      Lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image as they extend into the distance

•      The apparent point at which parallel lines receding in depth converge

•      A cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures

•      Use of the rules of linear perspective to create a two-dimensional image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion. 

•      Images closer to the observer move faster across the visual field than images farther away

•      The brain uses this information to calculate the distances of objects in the environment

•      The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects). How much we are stretching or flattening the lens. As things get farther away, the more the lens stretches. Use this to calculate approx. distances. 

•      The ability of the two eyes to turn inward, often used to focus on nearer objects

•      The ability of the two eyes to turn outward, often used to focus on farther objects

•      The location of objects whose images fall on geometrically corresponding points in the two retinas. Circle that covers visual field that allows you to focus on anything that is within that plain. 

•      Objects on the ___ are seen as single images when viewed with both eyes.

•      Objects closer or farther away from the horopter fall on noncorresponding points in the two eyes and are seen as two images.

§  Double vision. If visible in both eyes, stimuli falling outside of Panum’s fusional area will appear diplopic

•      The sign of disparity created by objects in front of the plane of the horopter

§  Images in front of the horopter are displaced to the left in the right eye and to the right in the left eye

•      The sign of disparity created by objects behind the plane of the horopter

§  Images behind the horopter are displaced to the right in the right eye and to the left in the left eye

•      A device for presenting one image to one eye and another image to the other eye

•      The technique of converging (crossing) or diverging (uncrossing) the eyes in order to view a stereogram without a stereoscope

§  “Magic Eye” pictures rely on free fusion. Demonstrate stereopsis.

•      An inability to make use of binocular disparity as a depth cue

§  Can result from a childhood visual disorder, such as strabismus, in which the two eyes are misaligned

Most people who have this dont even realize it

•      A stereogram made of a large number of randomly placed dots

§  RDSs contain no monocular cues to depth

§  Stimuli visible stereoscopically in RDSs are cyclopean stimuli

•      Referring to stimuli that are defined by binocular disparity alone

§  If you can free-fuse, you should be able to see the image, which is one square floating above the surface and a square-shaped hole poking into the surface

•      : In binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye

•      The problem is particularly vexing in images like random dot stereograms

§  Blurring the image: Leaving only the low-spatial frequency information

§  Uniqueness constraint: The observation that a feature in the world is represented exactly once in each retinal image

§  Continuity constraint: The observation that, except at the edges of objects, neighboring points in the world lie at similar distances from the viewer

•      How is stereopsis implemented in the human brain?

§  Input from two eyes must converge onto the same cell

§  Many binocular neurons respond best when the retinal images are on corresponding points in the two retinas: Neural basis for the horopter

§  However, many other binocular neurons respond best when similar images occupy slightly different positions on the retinas of the two eyes (tuned to particular binocular disparity)

•      A way of formalizing the idea that our perception is a combination of the current stimulus and our knowledge about the conditions of the world—what is and is not likely to occur

§  Thus, prior knowledge can influence our estimates of the probability of an event

•      A theoretical observer with complete access to the best available information and the ability to combine different sources of information in the optimal manner

§  It can be useful to compare human performance to that of an _____

•      A measure of the smallest binocular disparity that can generate a sensation of depth. How much of a shift in the visual field from eye to eye do we need to be able to perceive depth. 

§  : A misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye, and on the nonfoveal area of the other (turned) eye