Vision Science: Photons to Phenomenology
Course on vision, based on: "Vision Science : Photons to Phenomenology" by Palmer, Stephen E.
51 flashcards · Biology · by lakesare
What's the difference between how these balls reflect light?
matte sphere - reflects light equally in all directions, specular sphere - reflects it coherently, so that the angle of reflection equals the angle of incidence. All surfaces reflect some light except completely black ones (which absorb it all) and completely transparent ones (which transmit it all).And most surfaces are more matte than specular.In reality, there are neither totally black surfaces nor totally transparent ones. Even seemingly jet-black surfaces reflect a few percent of the photo…
What's ambient optic array?
The ambient optic array is the light coming toward a given point of observation from all directions. It is called "ambient" because the observation point is literally surrounded by light converging on it from all directions. This means that if your eye were at this observation point, either light reflected from environmental surfaces or light emitted directly from the radiant source would be available from every direction. Vision is possible at that observation point because environmental surfa…
What's distal stimulus VS proximal stimulus?
distal stimulus - light reflected by the 3-D object. proximal stimulus - 2-D projection on the retina. The size of an object's image in the eye is usually specified by its visual angle: the number of degrees subtended by the image from its extremes to the focal point of the eye. It is important to understand that this angle measures the spatial dimensions of the proximal stimulus, not the distal stimulus.
How to form a 2-D image of the 3-D world?
One way to form a 2-D image of the 3-D world is to place a pinhole at a given distance in front of an image plane or other 2- D surface inside an otherwise lightproof box. Such a device is called a pinhole camera. Because photons travel in straight lines, the light falling on each point of the image plane of the pinhole camera got there by being reflected (or emitted) from a particular point in environmental space.
What's the difference between orthographic and perspective projection?
Orthographic projection: parallel lines. Perspective projection: looking through the pinhole. One way of understanding the relationship between perspective and orthographic projection is to consider what happens when an object is moved farther and farther away from the pinhole of perspective projection.As this happens, the light rays projecting through the pinhole become more and more parallel so that, at an infinite distance, the light rays would be parallel, as they are in orthographic projec…
Why is orthographic projection mathematically simpler than perspective projection?
The mathematical simplification that results from orthographic projection is that the depth dimension of the world distances from image to objects is simply ignored, whereas all spatial information in the plane perpendicular to the viewing direction is preserved without change. This means that when the distance from the image to the object is large relative to the depth of the object (Figure 1.2.8B), orthographic projection is a good approximation of perspective projection. Close up, however, t…
How do we get the Horizon Line?
Same as Spectator height.
How do we get the vanishing point?
We should look at the line parallel to the line we're trying to draw.
What are these plates in rods and cones?
There are photopigments inside... The outer segment contains thin disks with pigment molecules embedded in them. Absorption of light by these molecules results in chemical changes that cause electrical changes in the inner segment. These electrical signals are transmitted to neurons via the terminal.
What's pigment bleaching?
This complex chain of events in the outer segment is called pigment bleaching because the change in molecular shape brought about by light also causes the molecule to change color. Before a rhodopsin molecule is bleached by absorbing light, it looks deep purple; afterward, it is almost transparent. Because it becomes transparent when it absorbs a photon, it is very unlikely to absorb another photon after it is bleached. Once bleached, the pigment molecules are restored to their prior unbleached…
What protein in rods?
Rhodopsin Rhodopsin (also known as visual purple) is a light-sensitive receptor protein involved in visual phototransduction. It is named after ancient Greek ῥόδον (rhódon) for rose, due to its pinkish color, and ὄψις (ópsis) for sight.[5] Rhodopsin is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR). The photopsins are found in the cone cells of the retina and are the basis of color vision. They have absorption maxima for yellowish-green (photopsi…
Name 2 theories of color vision.
1. Trichromatic Theory The first scientific theory of color vision was initially proposed in 1777 by George Palmer and independently rediscovered in 1802 by the British philosopher, Sir Thomas Young. Trichromatic theory assumes that color experiences arise from the activity of three hypothetical types of receptors with overlapping, but different, responses to different wavelengths of light. According to this theory, different patterns of activation correspond to the perception of different colo…
Who proposed Trichromatic theory Opponent Process theory?
Trichromatic theory - Thomas Young. This theory was later refined and extended by Maxwell (1855) and Hermann von Helmholtz (1867/1925), and it has since come to be known as the Young-Helmholtz trichromatic theory. Opponent Process theory - Ewald Hering.
What Trichromatic theory does not explain?
It provides no explanation of why color experiences are always lost in certain pairs: either red and green or blue and yellow always disappear together. The subjective experience of yellow does not appear to be a mixture of red and green in anything like the sense that the subjective experience of purple looks like the mixture of red and blue. Rather, yellow seems to be psychologically just as "primary" as red, green, and blue. As we just mentioned, there are colors that appear to be both red a…
What's a dual process theory?
Hurvich and Jameson realized that Helmholtz's and Hering's theories are not necessarily in conflictprovided one disregards Hering's claim that the opponent process mechanism resides in the receptors. In an elegant theoretical synthesis, they determined how two different stages of color processing might be able to account for a wide variety of findings.
What is the inverse problem when it comes to color?
Eye receives information about only one proximal variable (luminance), which is determined jointly by two distal variables (reflectance and illumination).
The ability to perceive the reflectance properties of surfaces despite changes in illumination and other viewing conditions is called _______________________.
color constancy
What phenomenon does this picture demonstrate?
Color constancy.
Name 2 ways to define categories.
Aristotle: instances of a category are all equally good, since each belongs via the iff condition. Berlin And Kay: category is built around the best examples. Not all colors are equally good, - not all reds are equally 'red'. We have a prototype 'red' in our minds. One of the key problems Berlin and Kay faced in their research on basic color terms was how to define color categories.The classical view can be traced to Aristotle, who proposed that membership in categories was defined by the prese…
What 'Et al.' stands for?
'Et al.' is an abbreviation of the Latin phrase et alia, which means 'and others'.
What's linguistic relativity?
Linguistic relativity claims that the structure of a language affects its speakers' world view or cognition, and thus people's perceptions are relative to their spoken language. Also known as the Sapir–Whorf hypothesis or Whorfianism. The origin of formulated arguments against the acceptance of linguistic relativity are attributed to Noam Chomsky.
Name strong and weak versions of linguistic relativism.
The principle is often defined in one of two versions: the strong hypothesis, which was held by some of the early linguists before World War II, and the weak hypothesis, mostly held by some of the modern linguists. Strong version: language determines thought and that linguistic categories limit and determine cognitive categories. Weak version: linguistic categories and usage only influence thought and decisions.
Explain, when it comes to linguistics: linguistic relativity (or Sapir–Whorf hypothesis, or Whorfianism) universalism
Lenneberg was also one of the first cognitive scientists to begin development of the Universalist theory of language that was formulated by Chomsky in the form of Universal Grammar, effectively arguing that all languages share the same underlying structure. The Chomskyan school also holds the belief that linguistic structures are largely innate and that what are perceived as differences between specific languages are surface phenomena that do not affect the brain's universal cognitive processes…
Classical set theory VS fuzzy set theory?
classical set theory: element either belongs to a set (1) or doesn't (0) fuzzy set theory: element can belong to a set in between 0...1. Classical set theory is compatible with the Aristotelian notion of category membership in the sense that each object either is a member of a given set or is not; there is no middle ground. Classical set membership can thus be conceived as a function that assigns to each object a value of 1 if it meets the necessary and sufficient conditions for set membership…
What's Berlin and Kay theory?
Berlin&Kay claim that as languages evolve, they acquire new basic color terms in a strict chronological sequence. The sequence is as follows: Stage I: Dark-cool and light-warm (this covers a larger set of colors than English "black" and "white") Stage II: Red Stage III: Either green or yellow Stage IV: Both green and yellow Stage V: Blue Stage VI: Brown Stage VII: Purple, pink, orange, or gray All cultures have terms for black/dark and white/bright. If a culture has three color terms, the third…
Name 1 example of linguistic relativity, and linguistic universalism.
linguistic relativity - Benjamin Lee Whorf, claims that Hopi treat time differently because their language doesn't have a concept of time. linguistic universalism - Berlin And Kay, claim that all languages acquire new basic color terms in strict chronological sequence. The universalist theory that color cognition is an innate, physiological process rather than a cultural one was introduced in 1969 by Brent Berlin and Paul Kay in their book Basic Color Terms: Their Universality and Evolution. Th…
What's Hopi time controversy? Hopi is a native american tribe
The Hopi time controversy is the academic debate about how the Hopi language grammaticalizes the concept of time, and about whether the differences between the ways the English and Hopi languages describe time are an example of linguistic relativity or not. In popular discourse the debate is often framed as a question about whether the Hopi "had a concept of time", despite it now being well established that they do. Whorf's study of Hopi time has been the most widely discussed and criticized ex…
What did Hubel and Wiesel receive a Nobel Prize for in 1981? Nobel Prize in Physiology or Medicine
firstly, their work on development of the visual system, which involved a description of ocular dominance columns in the 1960s and 1970s. secondly, their work establishing a foundation for visual neurophysiology, describing how signals from the eye are processed by visual parcels in the neo-cortex to generate edge detectors, motion detectors, stereoscopic depth detectors and color detectors, building blocks of the visual scene. 1. OCULAR DOMINANCE COLUMNS By depriving kittens from using one eye…
What's ocular dominance column?
Ocular dominance columns are stripes of neurons in the visual cortex of certain mammals (including humans) that respond preferentially to input from one eye or the other. The columns span multiple cortical layers, and are laid out in a striped pattern across the surface of the striate cortex (V1). Cross section through the lateral geniculate nucleus (LGN) of a macaque monkey. The dark layers receive input from the intact left eye; the light layers receive input from the blind right eye. The out…
Draw the architecture receptors horizontal cells bipolar cells
Neural inputs to an on-center, off-surround bipolar cell. The direct path (black connections) comes from receptors in the center of the receptive field. The indirect path of opposite polarity (gray connections) comes from receptors throughout the receptive field via horizontal cells. Retinal receptor cells synapse directly onto both bipolar cells and horizontal cells. The horizontal cells, in turn, synapse onto bipolar cells, thus completing an indirect pathway from receptors to bipolar cells i…
What 3 types of cells did Hubel and Wiesel discover in striate cortex?
SIMPLE CELLS The vast majority have an elongated structure, firing most vigorously to a line or an edge at a specific retinal position and orientation. Because such cells respond most vigorously to a luminance edge in the proper orientation and of the proper polarity (light-to-dark or dark-to-light), they are often called edge detectors. Other simple cells have receptive fields with a central elongated region that is either excitatory or inhibitory, with an antagonistic field on both sides of i…
Why do cataracts developed before 8th year of life have devastating effect on vision? Cataracts that develop after the 8th year of life have almost no lasting effects once they are removed. But cataracts that are present from birth have devastating effects on vision if they are not removed surgically during the first few months of life.
Wiesel and Hubel experiments showed that cortical cells in deprived kittens were still orientation selective, but they were not nearly as selective to edge orientation or direction of movement as those of normally reared kittens. These and other studies indicate that the visual system exhibits a critical period: an interval of time during which it undergoes rapid development owing to the effects of environmental stimulation. Both before and after the critical period, few effects of experience a…
On/off receptive fields & below visual acuity :-o
How is this afterimage explained?
A useful example of the doctrine of psychophysiological isomorphism is the opponent process theory of color perception (Hering, 1878/1964). It states that there are six psychologically primary colors structured into three pairs of opposites: red versus green, blue versus yellow, and black versus white. This analysis was based on insightful observations about the nature of color experiences.
Edge detectors VS line detectors?
When it comes to top-down VS bottom-up process - what is what?
bottom: retinal image top: temporally subsequent interpretations farther along the visual pathway are located at higher and higher levels Many people's naive intuition is that vision is essentially a bottom-up process. It begins with the sensory information in the retinal images and goes "upward" to perceptual and then conceptual interpretations. Most theorists concur that the early stages of visual processing are indeed strictly bottom-up. But there are good reasons to think that this cannot b…
What does back-propagration algorithm find?
Local error minimum Local versus global minima. Back propagation is guaranteed to find a local minimum on the error surface but not necessarily the global minimum. This graph shows an error surface with two local minima as well as a global minimum.
Why is additive color mixture - sums photons subtractive color mixture - multiplies % of photons transmitted? Additive mixture of lights (A) produces a combined spectrum that is the sum of the component light spectra.Subtractive mixture of pigments (B) produces a combined spectrum that is the product of the component transmission spectra.
When these lights are combined by superimposing them on the screen, their combination is literally additive: It is the simple sum of the photons from both beams. When the gels are combined by superimposing them, light must get through both filters, so there will be less of it than came through either filter alone. The mathematical rule for determining the combination of two color filters, when expressed as fractions or probabilities, is simple multiplication. To understand why, consider what ha…
Name 2 consequences of the fact that filters (paints, dyes) can't be metamers. Paints, dyes, and inks act as filters in the sense that they selectively reflect or transmit light at different wavelengths, removing the wavelengths that are absorbed.
As mentioned above, physically different filters and therefore physically different paints, dyes, and inkscan be considered "metameric" only with respect to certain specific lighting conditions. Pragmatically, this means that two paints, dyes, or inks that look the same in one light may look different in another light. For example, two articles of clothing that appear to be perfectly matched under the fluorescent lights of a store may look noticeably different in daylight or incandescent light.…
Is it possible to use paints to produce additive colors?
Somewhat surprisingly, there are ways of using two paints together that produce additive rather than subtractive color mixture. Instead of being mixed as liquids before they are applied to a surface, the paints must be applied separately in small regions at adjacent but non-overlapping positions. An example of this is shown in Color Plate C.2, where several areas filled with blue and yellow squares of different sizes are displayed side by side. When viewed from far enough away that the distinct…
Name 2 theories of vision: hierarchical feature detector model _____________________?
Spatial Frequency model An alternative to the hierarchical feature detector model of vision arose at the end of the 1960s; this model is known as the spatial-frequency model (F. W. Campbell and Robson, 1968; R. L. De Valois and De Valois, 1988), which is not at all intuitive. The spatial-frequency model proposes that the visual system analyzes the number of cycles of light-dark (or color) patches in any stimulus.
What does spatial frequency theory propose?
Just like any sound can be presented via the combination of simple waves using Fourier analysis, - any image can be presented using simple waves. Spatial-frequency theory proposes that the visual system analyzes the frequency of waves in the image, thus allowing to glean either borders (high-pass filter) general image (low-pass filter). If we pass the image A photograph of two penguins subjected to spatial filtering: (e) normal photograph; (f) high spatial frequencies filtered out; (g) low spat…
What's CSF in context of Spatial Frequency theory?
Contrast Sensitivity Function Demonstration of the shape of the contrast sensitivity function for luminance gratings. Spatial frequency increases continuously from left to right, and contrast increases from top to bottom.
Given these operators: convolute this cross:
The next step in calculating the convolution of the image with this edge operator is to "slide" the edge operator one pixel to the right and compute the output in the same way for the next two pixels in this row. Continue this procedure for each pair of pixels in each row of the image, and you will have computed the convolution of this local edge operator with the image. Note that the vertical edge operator has responded strongly to the vertical edges in the original image and nowhere else. Thi…
3.3 upwords - missed read all appendixes except for 1st 5.3.3 Computational Theories - missed I'm at page 588.
Bg: https://www.pexels.com/photo/low-light-photo-of-mountain-with-pine-trees-covered-with-fogs-1287081/ Spatial frequency, better understood: http://www.psy.vanderbilt.edu/courses/hon185/SpatialFrequency/SpatialFrequency.html
What does MT stand for [in visual cortex]?
Middle Temporal visual area or V5
What's a chromatic grating?
Explain the problem of depth ambiguity
Photons reflected by a surface at point A strike the retina at point A', but photons from A could also have come from: A1, A2, or anywhere along the ray from A' through A.
What's meant by the natural image as opposed to just random image?
Random image: looks like TV static Natural image: trees, cities random image natural image
What's the proof of binocular rivalry?
Grossly mismatched images in the two eyes result in the observerseeing only one image at a time, a phenomenon known asbinocular rivalry or binocular suppression. Withsmall patterns subtending 1° of visual angle or less, rivalry tendsto be holistic, the two entire images alternating in perceptualexperience over cycles lasting about 1-4 seconds. With largerimages, rivalry tends to lead to piecemeal perception of differentparts of the two images at once. Binocular rivalry. Fuse the two squares usi…
Provide 2 explanations for why we perceive the rotating figure. Why might the visual system be selectively ''tuned" to perceive rigid rather than plastic motions? The kinetic depth effect. A 3-D bent-wire object is illuminated from behind, and its shadow is cast onto a translucent screen viewed by an observer. When stationary, it looks like a flat 2-D figure; but when rotated, it pops into a compellingly 3-D rotating object.
empirical probability - rigid motions are much more probable than corresponding plastic ones if the image motion is consistent with a rigid motion gestalt principle of Prägnanz (most simple explanation) - the visual system prefers the simplest interpretation, given the prevailing conditions of stimulation. The rigid interpretation can be counted as simpler because it does not involve changes in the object's shape over time and so could be more economically represented and processed. This is ano…