Cornell Prelim 1

86. Describe the basic arrangement for a VR system like Google Cardboard. Include the position of the display and the optics required (LaValle and lecture)

- Basic VR system is display, two lenses, and your eyes - Distance between lenses and display has to be 1/number of diopters

45. How does one measure the contrast sensitivity function (CSF) of a human observer? Describe the contrast sensitivity function differences in adults and 3 month olds. What does this imply for information presented to children on a display?

- Give you gratings of different frequencies and reduce the contrast until you can't see it. Find out when it's just enough that you can see it and when it disappears - In adults, peak sensitivity is around 4 cycles/degree, then falls off to about 50 cycles/deg -> Younger has lower acuity, shallower curve --- Need to take into account ages Be careful talking about abilities of an infant, because their acuity is low Infants should be shown lower frequency, higher contrast

10. The famous blue and black (or white and gold) dress is seen differently by different people. Why?

-Different people interpret the reflectance of the dress in different ways: --some people perceive the dress as a blue and black under bright illumination --Others perceive it as white and gold under dim blue-ish illumination

21. What is the relation between lens flare and perceived brightness. Why does this work?

-Lens flares are caused by light scattered in a lens system from a bright light, so we naturally associate these flares to a bright light source -By adding lens flares to objects (eg. candles), it can increase our perceived brightness

67. What is the simplest model of surface texture that creates the perception of surface shape from shading? How is this used to shade a sphere with one light source? What are two additional effects that improve how the shading looks? (W)

-Simplest Model: Lambertian Shading -Light is selectively absorbed and reflected depending on the color and some is scattered back through the surface out into the environment -Specular Shading and Ambient Shading -> Specular shading: the light that is reflected directly from a surface is called specular. Ambient shading: ambient light is the light that illuminates a surface from everywhere in the environment, except for the actual light sources. Cast shadows: an object can cast shadows either on itself or on other objects

71. What is cortical magnification? How does this relate to the eye chart of Anstis with letters of varying sizes as a function of eccentricity? (W)

-Where the number of neurons in the visual cortex responsible for processing the visual stimulus varies as a function of the location of the stimulus in the visual field----I.e. Number of neurons processing image location of the stimulus -Chart of Anstis: When focused at the center, you can both clearly read the small letters as well as the large periphery ones, because less neurons are necessary to process larger stimulus in the periphery. Don't work when sizes are flipped since there aren't enough neurons to process the small letters

52. What is dithering? Why is it effective perceptually?

-strategy of high resolution with low-intensity levels (just creating different densities of dots) -All colors are approximated by colors available from the palette in the intensity levels ---- It is effective because it uses many small points to create the illusion of intermediate intensity levels Takes advantage of our eye's tendency to mix colors together [Visual system averages all the colors (greys)] Creates smooth and better transitions within the image

33. Provide a rough estimate of the spatial frequency of the grating shown on the blackboard (in cycles/deg) and explain how you arrived at this estimate. Approximately, how many lines would there need to be to approach your acuity limit? (also tell us where you are sitting).

1 thumb → 2 degrees 15 lines -> 7.5 cycles 7.5 cycles / 2 degrees → 3.5 cycles/degrees Approximately, how many lines would there need to be to approach your acuity limit? (also tell us where you are sitting). Acuity limit = 50 cycles/degree 100 lines/degree 2 degrees → 200 lines --- -Count lines (½ that for cycles)-Degrees = take thumb (KNOW ANGLE) and go across → ex: 10 lines/1 degree (5 cycles/degree)-Approach Acuity Limit: measure thumb widths across, multiply by 100

9.1. How many "bits" of luminance are available with a display that has only two intensity values (i.e., a monochrome display). 9.2. How many are needed to produce photographic quality images? 9.3. What are three factors that have bearing on this number.

1. 1 bit 2. 10 bits (1024 levels ~~ 1000 levels) 3. Three factors: 1. Screen range: range of intensities the screen can produce 2. Particular image (smooth intensity variations require more bits) 3. Screen gamma (optimizing gamma minimizes the number of bits needed)

85. Describe both astigmatism and presbyopia. In each case, describe the cause and the effect of these. (La Valle and lecture) 28. What is astigmatism? 25. What is presbyopia? Can you avoid it? What does this do to the near and far points?

1. A common vision condition. Cause: the cornea is irregularly shaped or sometimes because of the curvature of the lens inside the eye, distortions at different angles Effect: Blurred vision. 2. a. The lens in the visual system hardens with age. It can't be avoided, but we can correct it with progressive lenses. Cause: The distance between near and far points becomes closer and closer with age. Effect: The near point shifts farther, and the far point shifts closer

14. What causes motion sickness? How does this relate to the mismatch hypothesis? Why might motion cause sickness in the first place? Why is a passenger more likely to get sick than a driver even when they are both keeping their eyes on the road.

1. Active Conflict between vestigial and visual. Semicircular canals with fluid in our ears that tell our brains that we are moving. If there's a violation in our expectations, we feel sick. 2. Motion sickness is caused by a conflict between our visual and vestibular system. Therefore, when we see movement but do not feel movement, we feel sick. 3. Your body think that it has been poisoned since visual/vestibular errors are used as a cue that you've been poisoned. Thus you may throw up 4. Driver has good expectation of motion of the car; passenger cannot as easily anticipate the movements that will happen since they are not in control.

12. Describe two aspects of virtual reality that can make us sick.

1. Active Conflict: Action does not equal vision 2. The larger the visual field, the more likely 3. Update rate for slow computers

20. Describe three recommendations for children to reduce their chance of getting high myopia? What happens to the eyes of those that develop high myopia? Is myopia inherited or is it entirely environmental?

1. Do not wear glasses for close work. If you can read without your glasses, do it. 2. Consider getting progressive lenses 3. Spend more time outdoors - Myopia: Nearsightedness → Eye is becomes too long and too powerful, so the light rays will focus in front of the retina - -Environmental: There are some correlations of myopia with education and urban living (Hong Kong students with their high myopia rates and the Taiwanese medical students with increased rates)--Too much close work (reading books etc.)--Lack of sufficient bright light-Genetic: myopia in offspring from myopic parents with up to 3x highe

13. What are the conditions that produce the appearance of self-motion for a human observer? What was wrong with the drum studies? How would you design a perceptually 'efficient' automobile simulator if the observer limited his/her direction of view to straight ahead?

1. Expansive motion (when you walk toward something everything expands) 2. linear motion in the periphery produces best self-motion 3. radial or expansive flow in center of periphery produces second-best self-motion --- 1. Drum studies not good simulation for normal movement. Showed radian can produce movement in central 10 degrees ----- Think about rides in Disneyland, they're: -linear self-moving -Don't need high-res -lights in periphery to make it feel like motion

4.1. What is the gamma of a display? 4.2. Roughly what is the gamma of your visual system? 4.3. How does the gamma of your visual system affect the apparent luminance of an intensity ramp? 4.4. How does gamma of a digital camera and a screen help in the compression of images

1. Gamma: the distribution of intensities; Output (Brightness) = Input^(y) (Intensity) - If linear → y = 1 2. Visual System: ~0.5, in bright regions the visual system needs larger intensity changes to be visible 3. In brighter regions, the visual system needs larger intensity changes to be visible. A larger gamma creates a larger contrast between light and dark. 4. Compressive non-linearity helps to reduce the range of responses needed to represent an input with a large range of intensities

83. Describe 5 ways to make a spot appear to move.

1. Move it 2. Adapt to motion then observe the dot (motion aftereffect): Caused by an imbalance of neurons responding to motion (fatigue), so neurons will still think image is moving 3. Autokinetic: stare at a stationary point of light → eye fatigued → eye moves → perceived movement in space 4. Induced Motion: move the reference frame (eg. Watching the train leave on the next track over, who is actually moving?) 5. Strobscopic: When the stimulus is viewed in separate stages (flash lights to only show certain frames), can cause the appearance of motion

50. For virtual reality glasses with a visual field of 180 degrees, how many pixels across are needed to be at the acuity limit. If the display is binocular with 120 degrees in each eye, how many pixels are required for each eye?

Acuity limit = 50 cycles/degrees = 100 lines/degree under ideal circumstances = 100 pixels/degree ---- Acuity Limit: 180 degrees * 100 PPD = 18,000 pixels ---- Per Eye: 120 degrees * 100 PPD = 12,000 pixel for each eye

7. What is high dynamic range (HDR) imaging. How does this approach increase the apparent range of an image?

Capturing high dynamic range images and creating images that look high dynamic range on low dynamic range displays ---- Goal: Increase contrast 1. Expands low and high contrasts by photographing the two extremes and thus get contrast on every part of the screen 2. Re-maps luminance to screen range and maintain contrast across different areas of the image

69. Describe both chromatic aberration and spherical aberration in a lens. Describe both the cause and the effect? (LaValle)

Chromatic aberration: When colors are incorrectly refracted by the lens, thus fails to focus all colors to the same pointEg. Blue text vs red text on a black background: people may perceive red text as closer (60%), blue text as closer (30%), or the same Cause: longer wavelengths traveling more quickly through the lens. All wavelengths are not focused equally. Lens is bending different wavelengths differently Effect: a different focal plane for each wavelength of color. Chromatic Aberation: Spherical: Not perfectly spherical in all directions Cause: rays further away from the lens center being refracted more than rays near the center Due to the spherical shape of the lens Effect: some blur that cannot be compensated for by moving the object, lens, or image plane The image might instead focus onto a curved surface rather than the imge plane

63. Describe the four stages of information visualization. What is the role of feedback in these stages (W)

Collecting: Collection and storage of data Preprocessing: A preprocessing stage designed to transform the data into something that is easier to manipulate. Usually there is some form of data reduction to reveal selected aspects. Data exploration is the process of changing the subset that is currently being viewed. Mapping: Mapping from the selected data to a visual representation, which is accomplished through computer algorithms that produce an image on the screen. User input can transform the map, highlight subsets, or transform the view. Generally this is done on the user's own computer Perceiving: The human perceptual and cognitive system (the perceiver). --- Feedback loops are used throughout these stages. The longest feedback loop involves gathering data. There are also feedback loops concerning data exploration and view manipulation of the visual mappings

29. Why is skin so hard to model in computer graphics (two reasons).

Complex reflectance functions and human visual system very sensitive to reading faces

36. Describe the roles that the cornea and lens play in focusing an image.

Cornea has a fixed power of ~40 diopters Lens has a variable power of 10-22 diopters -> Total is 50-62 diopters and allows focusing at different distances --- Light passes through the cornea (starts the focusing) to the lens (changes its focal length). --- Both focus light onto the retina The lens allows the image to be focused on the retina

58. What does it mean when we say that the visual system uses a "sparse" representation?

Data are sparse- events are localized in time and space The visual system is near optimal at finding a sparse* representation of natural scenes *Sparse: a high proportion of neurons show activity near zero

1. Describe the differences between efficient, inefficient and restrictive display systems. Do we need all displays to be efficient?

Efficient: info = limits of sensory system Inefficient: info > limits of sensory system Restrictive: info < limits of sensory system ---- No. Certain images can capture our attention could be above or below limits of visual systems

42. Why doesn't an image normally disappear if I fixate very accurately at one point? What does one have to do to make it disappear?

Fixational eye movements: drift, micro-saccades, tremor keep you from being still Our visual system depends on change in receptive fields, otherwise they will stop firing => Fixate on blurry stimulus so that it will disappear (Blurry enough where it doesn't create a lot of change in receptive fields)

57. Describe four applications that use eye tracking in virtual or augmented reality.

Foveated rendering Avatars with appropriate eye movements Game design (e.g. aim with eye direction) Pay per glance (ads dependent on whether the viewer viewed the product)

66. Describe the three primary stages of perceptual processing according to Ware (W).

In Stage 1 (parallel processing), information is processed in parallel to extract basic features of the environment. In Stage 2 (Pattern perception), active processes of pattern perception pull out structures and segment the visual scene into regions of different color, texture, and motion patterns. In Stage 3 (visual working memory), the information is reduced to only a few objects held in visual working memory by active mechanisms of attention to form the basis of visual thinking.

19. In terms of the power of the lens and cornea, describe the difference between someone near-sighted and far-sighted. Describe how lenses help these people.

Near sighted: Too much power. Unable to see things clearly unless they are relatively close to the eye (Lenses with negative diopters help) Far sighted: Not enough power. Distant objects are seen clearly but near objects appear blurred. (Lenses with positive diopters help) --- Lenses correct their vision by removing extra diopters of power for near-sighted people, and giving far-sighted people more diopters of power.The lens bends the light rays before they enter the eye.

38. What is foveated rendering? What are the advantages over standard rendering?

Only rendering more clearly what is received by the fovea, because what is in the periphery is not in focus. Technique to put high resolution rendering where the observer is looking ----- Don't need to render the entire image, only what's in fovea area. Computationally less expensive

31. Provide two examples that demonstrate that shadows play a role in the interpretation of objects.

Penumbra: the penumbra of a shadow allows us to tell the difference between the lightness and brightness on a surface (misjudge of changes in material vs a shadowed area) Where a shadow is located can tell us how far an object is above the ground (teapot on a surface)

16. Plot the relationship between scotopic and photopic spectral sensitivity and use this plot to explain the Purkinje shift and why red light or red goggles are often used under scotopic conditions.

Purkinje Shift: As lighting conditions dim, the relative proportions of rod and cone contributions shift, resulting in the luminance of colors changing (reds become darker, blues become brighter). This is because our rods (scotopic) and cones (photopic) have different sensitivities to different wavelengths of light. Our scotopic photoreceptors are more sensitive to smaller wavelengths and our photopic photoreceptors are more sensitive to larger wavelengths Red light or red goggles are used under scotopic conditions because they will shift the wavelengths we perceive back into the range perceived by our photopic photoreceptors (cones). Since our cones have better acuity this helps to see better at night.

26. Describe three cues that observers use to discriminate lightness from brightness.

Ratios: ganglion cells calculate ratios Take ratio of intensity to the surround Penumbra: the softness on the edges of shadows Indicates illumination change Multiplication across borders: ratios of intensity are maintained along illumination borders Co-planar hypothesis: surfaces in the same plane are assumed to have the same illumination without other cues that signal a shadow.

34. Provide a simple map of the pathways that take visual information from the eye to the brain. Include a discussion of the left and right visual fields and the superior colliculus.

Rods + cones → ganglion cells → optic nerve → LGN → (0.9 of LGN) cortex or (0.1 of LGN) superior colliculus ---- Light entering eye triggers photochemical reactions in rods and cones at back of retina → chemical reaction in turn activates bipolar cells → information is sent to visual cortex via thalamus Information from right visual field goes to left eye and information from left visual field goes to right eye, 90% of optic of LGN projects to the cortex while 10% projects to superior colliculus

76. Describe the relationship between stimulus intensity and intensity of perception that Fechner and Stevens found. How does this relate to the monitor gamma? (W)

S= aI^n where S is the perceived sensation, I is the stimulus intensity, law states that S is proportional to L raised to the power n. Just as perceived brightness is a very nonlinear function of the amount of light emitted by a lamp, monitor screens are also nonlinear in the opposite direction. The relationship of physical luminance to the input signal on a monitor is approximated by a gamma function. So a monitor with a gamma of 2 will exactly cancel a brightness power function exponent of 0.5, resulting in a display that produces a linear relationship between voltage and perceived brightness

68. What is saccadic suppression? How does this help with foveated rendering? How can the loss in sensitivity be used to increase the size of a virtual room?

Saccadic Suppression: Acuity drops tremendously during eye movement to block out the blur → large changes in object locations are not detected (blinks, saccades etc.) -Foveated rendering requires accuracy and low-latency eye tracking, but saccadic suppression allows leniency (delays) for update times-Just add to resolution over time instead -With each saccade, the system will alter the room to turn minutely so that the user is less likely to bump into objects/walk too far away, causing you to actually walk in a circle when you think you are walking straight

55. Explain the contrast sensitivity function under scotopic, mesopic and photopic conditions.

Scotopic: low contrast sensitivity (lowest curve) Mesopic: medium sensitivity (middle curve) Photopic: peak contrast sensitivity (highest curve) Acuity drops as you go from photopic → mesopic → scotopic

40. Describe 2 similarities and 2 differences between the processing of objects along the visual pathway and the processing of objects by deep networks.

Similarities They are using a hierarchical nature and multiple layers that have difference receptive fields, and they get more complicated as you move up through the system The kinds of receptive fields they learn is very similar to the brain (learning similar kinds of receptive fields) Differences The way they learn is different- deep networks require huge datasets of labeled data, but the visual pathway does not learn on labeled data The visual pathway has a lot more feedback than deep networks

32. What is a specular reflection? What is a diffuse reflection? How can these two features combine to affect the perception of a material?

Specular Reflection: light is deflected from a smooth surface and exit angle = entry angle Diffuse Reflection: light is deflected from rough surface and reflected rays scatter in arbitrary directions. Together, they provide the accurate reflection of light bouncing off an object (directional diffuse) (can go from shiny to matte)

41. Describe the difference between supervised an unsupervised learning.

Supervised learning learns on a labeled dataset, while an unsupervised model provides unlabeled data and tries to extract patterns and structures in the given input data --- Supervised learning has labeled data, direct feedback, and predicts an outcome/future Unsupervised learning has no labels, no feedback, and finds hidden structures in data.

35. Distinguish between hyperopia, myopia, and astigmatism including the symptoms, causes, and possible remedies of each.

Symptoms Causes Remedies ----- Myopia near-sightedness Too much power (too many diopters) Negative lens Do not wear glasses for close work. If you can read without your glasses, do it. Consider getting progressive lenses Spend more time outdoors ---- Hyperopia far-sightedness Not enough power (too few diopters) Glasses with positive correction ---- Astigmatism Distorted vision due to the eye being misshaped, light rays scattered Different angles have different diopters Corrective lenses/refractive surgery

6. Explain why the dynamic range of a display depends on the amount of stray light. Provide an example.

The luminance ration depends on stray light. Therefore, dynamic ranges of displays depend on stray light. Stray light occurs with any display as long as there are objects within the room for the display to reflect light to the object and back onto the screen. Let's think about movie theaters. The exit signs create stray light. If 1% of light is emitted is reflected back onto a screen with 1000:1 range, the screen will become 1010:11 range (due to 10 units of stray light.

24. Explain why a negative lens helps a myope to see better. 87. Why do myopes use concave lenses (LeValle and lecture).

The visual system has too much focusing power, and a negative lens helps reduce focusing power. A negative lens diverges the light that enters the eye, pushing the light towards the periphery, giving the myope less visual power. Concave lenses = negative lenses (one concave surface and are thinner in the center than at the edges.)

73. Provide a brief explanation of the Cornsweet illusion (W) 75. What is the Cornsweet illusion (a picture could be useful)? How has this effect been used by painters? (W)

The visual system perceives the upper surface to be a dark-colored surface exposed to bright illumination, and the lower surface to be a pale-colored surface in shadow, and this gives us the illusion that the reflectance of the lower surface is brighter than the upper surface, while in fact they have the same reflectance. The Cornsweet illusion suggests that the brain constructs surface color based largely on edge contrast information. Painters enhance edge contrast in order to make objects more clearly distinct (esp. given paint's limited dynamic range)

79. Neurons are the basic unit of computation in the brain. How do neurons communicate with each other? Name one way in which they are similar to transistors, the basic unit of computation in a computer. (W)

They communicate by receiving signals in dendrites and sending signals along axon to other neurons it is connected to. The rate of firing can be increased or decreased as the neuron is excited or inhibited. Like transistors, neurons respond with discrete pulses of electricity.

2. What will be perceived as brighter? B) A 100 nit lamp that produces most of its energy in the range of 500 to 540 nanometers or a 100 nit lamp that produces most of its energy between 650 and 700?

They will be perceived as equally bright because nits take into account visual sensitivity.

53. What does the CSF say about the differences between the visual system of the infant and the adult?

Visual system of an infant has less contrast, and adult has more contrast Children have worse acuity

62. Name 4 reasons we may want to convert a non-visual data set into a visual data set (W)

Visualization: 1. Provides ability to comprehend huge amounts of data 2. Allows the perception of emergent properites that were not anticipated. 3. Enables problems with data to become immediately apparent. 4. Facilitates understanding of both large-scale and small-scale features of data 5. Facilitates hypothesis formation

27. What type of lens does a virtual reality display require if the display monitors are mounted 10 cm in front of the lens and are intended to be viewed at infinity? What type of lens is required if the observer normally requires -2 diopters of correction?

Want to see the display as though its at infinity Want positive lenses because we want to make something very close look very far Like adding a magnifying lens 10 cm = 0.1 m 1. Need a 1/0.1 = 10 diopters lens 2. Need a 10 - 2 = 8 diopters lens

78. Explain Weber's law regarding lightness differences. How much more luminance does a patch need to have to stand out from the background? (W)

Weber's Law: If we have a background with luminance L and superimpose on it a patch that is a little bit brighter (L + δL), then the value of δ that makes this small increment just visible is independent of the overall luminance. Thus, δL/L is constant. Note that this law only applies to small differences. When large differences between gray samples are judged, other factors become significant. Typically, under optimal viewing conditions, we can detect the brighter patch if δ is greater than about 0.005. In other words, we can just detect about a 0.5% change in brightness.

56. How can flicker above the critical fusion frequency still have an effect on a human observer?

When eyes are moving, it's strobing when it moves around (flashing three colors), you won't notice any problem when stationary but when moving it starts to strobe --- think purple ball vs. red-blue-green circle

77. How does the visual system factor out the amount and color of the illumination when making lightness decisions? (W)

When making lightness decisions, the visual system factors out the amount and color of illumination through adaptation (allows the visual system to adjust overall sensitivity to ambient light levels- decrease sensitivity at high light levels and increase sensitivity in low light levels) and lateral inhibition (as brightness increases, neurons are stimulated more but also inhibited more creating perception of constancy).

82. What is the uncanny valley? Provide a graph (label the axes). Describe the perception at different points along the curve.

With the human form, graphically "nearby" can be eerie/disgusting (polar express/Shrek). Graph: familiarity vs. human likeness. sharp dip is the uncanny valley

54. Are natural scenes redundant? Describe 3 forms of statistical redundancy. Why is this important for understanding compression? Describe how the visual system takes advantage of this?

Yes - 1. Nearby points are highly correlated 2. Data are sparse- events are localized in time and space In an area where nearby points are not correlated, there is likely an edge 3. Data show continuity across space, time and frequency The sparse structure shows continuity across space and scale - We can represent data with a minimum number of units - Spatial resolution: respond only to local differences, periphery- the local range is larger Temporal resolution: respond to only local changes over time

44. Who was Frank Rosenblatt and what is the Perceptron? What can a Perceptron learn and not learn? How is this different from 'deep' learning techniques?

a. Frank Rosenblatt was a psychologist at Cornell who invented the Perception. The Perceptron was the first artificial neuron-based computer. It was a 500-neuron, single-layer neural network and was attached to a 400-photocell optical array. b. The Perception can learn to classify data, but it cannot learn hidden patterns. Can only learn linearly separable data c. Deep learning techniques involve multi-layer hierarchical networks They include massive amounts of labeled data and more powerful dedicated computers

8. Describe four differences between foveal and peripheral processing.

foveal 1. mostly cones (less sensitive to light) 2. more sensitive to high wavelengths 3. more detail needed 4. responds faster to flicker peripheral 2. rods 2. low wavelengths 3. less 4. slower

30. How does the early visual system compute ratios? Why is this a good thing?

log(center) - log(surround) = log(I1) - log(I2) = log(I1/I2) (calculates ratios) Yay b/c Due to light constancy, our perceived brightness of an object is unchanged despite changes in illumination

3. Calculate the visual angle of your thumb at arms length, the screen in front of you and your phone. Show your calculations.

thumb at arm's length = 1 visual degree

5. Roughly, for a single image, what is the range of intensities found in the real world, hard copy (e.g., magazines)?

~1000 levels (10 bits) 1. Real world: 500:1 luminance ratio 2. Hard copy: 30:1 luminance ratio

43. Describe the five different types of eye-movement and an example of when each is used (or describe the eye-movements that occur as you are running around your house trying to catch your cat - or playing tennis).

1. Saccades --> Shifts center of gaze from one visual field to another, used for orienting gaze towards object of interest 2. Smooth Pursuit --> Eye tracks movements of an object 3. Fixational --> Maintain the visual gaze on a single location 4. Vestibular Ocular Reflex --> Movement of the head produces change in eye position to allow stabilized vision 5. Opto-kinetic nystagmus --> Involuntary response to movement

51. Describe the steps for producing anti-aliasing on a computer screen. Why is this done and what does it achieve?

1. Take high resolution images 2. Blur (remove frequencies before aliased) 3. Subsample Removes artifacts from normally sampling an image and creates an image an image that appears to have better resolution.

2. What will be perceived as brighter? A) A 100 watt lamp that produces most of its energy in the range of 500 to 540 nanometers or a 100 watt lamp that produce most of its energy between 650 and 700?

100 watt lamp that produces most of its energy between 500 to 540 nanometers will be brighter because that is where we are most sensitive to light. (Based on a curve)

22. Why would late night stores blast 17,000 hertz tones?

A frequency that mostly only teenagers can hear, this will deter underaged youths from going to such late night stores. Our sensitivity decreases as we age, and it is painful to hear those noises.

65. Provide an example of a stage in visual processing where there is considerable compression (hint the optic nerve). What is the magnitude of the compression?

About 1.2 million nerves in the optic nerve 120 million photoreceptors in the eye Massive compression in optic nerve Really good resolution in periphery but the optic nerve compresses it losing that extra detail -> 100:1 compression

64. Are abstract visual representations based only on cultural knowledge? Explain (W)

Abstract visual representations have some grounding in cultural knowledge based on different cultures' unique perceptions of different things, but they aren't only based on cultural knowledge; it is possible to have a new semiotics based not on philosophical claims for symbols being arbitrary, but instead on scientific evidence.

37. Why is accommodation a problem for virtual reality. Why is this not a significant problem for those older than 60?

Accommodate is adjusting lens for something really close -VR headsets have a fixed focal length -Distance of the screen is fixed, but Young try to accommodate when focusing on close vs. far objects - Older than 50 (60) cannot do this

17. What is the Hermann grid and what is the current explanation? 74. Explain the illusions created by the Hermann Grid and Chevreul/Mach bands in terms of receptive field spacing. Diagrams would be useful here. (W).

An image with black boxes and white lines in between each box such that when you look at the image, you see block dots in the intersection of each black box but they aren't really there. Current Explanation: the center/surround cells that signal the white of the intersections are more suppressed than are the center/surround cells that signal the white of the lines between the intersections. In the Hermann grid, we see gray spots at the vertices of the grid because the surround/inhibitory parts of the receptive fields are stimulated more at the vertices than at edges, and the response is therefore lower at the vertices. The receptive field of the visual system is divided into center and surround areasFor on-center ganglion cells, the cells' response are maximized when there's stimulation to the center only, and not to the surround. When both the center and surround are stimulated, the response decreases.

23. What role does lateral inhibition play in lightness constancy?

As overall illumination increases, ganglion cell is more excited but also more inhibited by neighbors, creating constant perception of brightness -Lateral Inhibition: When an excited neuron reduces the activity of its neighbors -Lightness Constancy: Our ability to perceive the reflectance of a material despite changes in illumination. Uses proportionality (ratios) with its surroundings to perceive independent of its intensities -Lateral inhibition is important for edge detection, it increases the contrast of the colors. We use lightness constancy to use ratios to detect these differences independent of intensity

18. Suppose that you have a near point of 10 cm and a far point of 25 cm. a. What is your condition? (e.g., hyperope?) c. How should this person be corrected? d. After correction where will this person's near point and far point be located?

MATH -Max D = 1/NP = 1/.1 = 10 D Min D = 1/FP = 1/.25 = 4 D (person is like 40 years old) Therefore range is 4D-10D We want FP to be infinity → new Min D is 0, Max D is 6 D, and therefore, new Np = ⅙ = .167 m = 16.7 cm a) Myopia (negative correction), also presbyopic c) Use progressive lenses where -4D lens: on top +2D lens: on bottom d) np = 1/maxD = 1/6m 0D = 1/fp, fp = infinity

48. For a 1 meter wide television with 4000 pixels across, how far away should it be, to be at the highest visible resolution (assume 100 pixels/deg PPD).

MATH 4000 pixels * (1 degree/100 pixels) = 40 degrees tan(𝜃) = size/ distance tan(40) = 1 m/distance 1/tan(40) = distance/1m therefore, Distance= 1m/tan(40)

49. For a 1.5 meter television screen at 1 meter, how many lines are required to be at the highest visible resolution (assume 100 PPD).

MATH tan(𝜃) = size / distance = tan(𝜃) = 1.5/1𝜃 = 56.3 degrees (number might be off; think i converted to degrees on Python lol) 56.3 degrees (100 PDP) = 5630 pixels