Visual Perception Flashcards

Question

one foot candle = __ lux

Answer 1

507nm 507nm corresponds to 1700 lumens/watt

Answer 2

if multiple wavelengths are present in a light source, you can add lumens from each wavelength to determine the total luminous power

Answer 3

absorb some of the light incident upon them - this means that light leaving the filter has a different spectral composition (different wavelengths that make up the light)

Answer 4

only allow a smalll range of wavelenghts to pass through specified by 2 quantities 1. location of peak: which wavelength range most easily passes through the filter 2. half-height bandwidth: indicates the selectivity of the filter. higher half-height bandwidth = less sensitive filter

Answer 5

Narrow band filter: allow only a small range of wavelengths to pass through Interference filter: Allow only 1 wavelength to pass through Broadband filter: Allow a large range of wavelengths to pass through Long pass filter: allow only long wavelengths to pass through, blocking short wavelengths that could cause cataract formation

Answer 6

long pass filters Sunglasses can act as a neutral density filter by equally reducing the transmission of all wavelengths

Answer 7

transmit all wavelengths equally, minimizing color distortion this will decrease the amt of light transmitted from the eye to the visual cortex = slower neural response

Answer 8

Pt sees a pendulum swinging back and forth b/c each eye equally transmits visual signal to the visual cortex When you place a ND over one eye the neural response of a visual cortex is SLOWED and the pendulum appears to move in an ellipse rather than back and forth plane - place ND over right eye = counteRclockwise - place ND over left eye = cLockwise

Answer 9

measure density of APD - place ND over unaffected eye until APD affected disappears

Answer 10

same luminance from every viewing angle (matte paper) L = RE L = luminance (foot-lamberts) R = reflectance E = illumination (foot-candles)

Answer 11

unequally scatter light in different directions (shiny piece of silver)

Answer 12

amt of light falling on the retina T = LA T = retina illumination (troland) L = luminance of the viewed surface A = Area of the pupil

Answer 13

general illumination falling on a tilted surface is related to the intensity of light source by inverse square and cosine laws E = Icos(angle)/d6^2 I = intensity of the point source angle = angle of tilt d = distance of point source to surface

Answer 14

T = LA A = pi(R)^2 A = pi(1.5mm)^2 T = (50)(7) = 350 trolands

Answer 15

- Vision under dim lighting (primarily rods) - lack of color discrimination - good sensitivity

Answer 16

Vision under bright light conditions (primarily cones) - excellent VA and color discrimination - poor sensitivity

Answer 17

a photopigment responds to absorption of a photon (quantum of light) in a manner that is completely independent of the wavelength of a photon - the wavelength of a photon only determines the probability of absorption of photon by the photopigment - as a result, once photon is absorbed, all info about wavelength of the photon is lost In simple terms, the principle of univariance means that the information about a color or brightness comes from the total amount of light hitting a receptor, regardless of what combination of colors or brightness levels produced it. So, a receptor (like a cell in the eye) can't tell what combination of colors or brightness levels made the light, it just knows how much light there is.

Answer 18

difference between the sensitivities of the scotopic and photopic system 650 nm = rods and cones are equally sensitive 507nm = scoptic system 555nm = photopic system

Answer 19

- increase illumination = longer wavelengths appear brighter due to shift from scotopic system - helps adapt to different lighting conditions (transition from scotopic to photopic conditions and vice versa) (red and orange appear brighter in photopic conditions while red-green appears brighter in scotopic conditions)

Answer 20

- how threshold changes as we spend more time in the dark (regeneration of rods and cones) - threshold and sensitivity has an inverse relationship

Answer 21

determined by measuring the threshold at a certain wavelength - transitioning from bright light to darkness - rod-cone break = rods take over as primary source of seeing light

Answer 22

- mathematically describes dark adaptation, it says that the photopigment regeneration is the sole cause of dark adaptation

Answer 23

- how well an individual can pick out a spot of light from a background of slightly different intensity - increase the intensity of light until just perceived light is detected against a background with slightly different intensity ( difference btw spot of light and background aka JND), the background intensity i sthen increased, and the pts threshold is determined again

Answer 24

when 10% of rhodopsin molecule are bleached resulting in the closure of critical number of Na+ channels within the rod photoreceptor membranes

Answer 25

assumes webers law holds true for stimuli intensities above the threshold

Answer 26

Scotopic system b/c it has larger pixels, 1:1 ratio

Answer 27

photopic system single or few cones with a single ganglion cell

Answer 28

describes the relationship between the intensity and area of a stimulus that is below the threshold for spatial summation. It says that the total number of quanta (photons) for a stimulus is below the critical diameter constant - critical diameter = size of the pixel in the visual system, scotopic system has a larger critical diameter. The size of the test light must be less than the critical diameter for spatial summation to occur - if the critical diameter is greater than the size of the test light then you have to increase the intensity of the stimulus in order for the pt to detect test lights b/c photons from the stimulus are now falling on multiple ganglion cells IA = C I = stimulus A = stimulus area C = constant Summary: - stimuli less than the critical diameter can still be seen if the area is increased - area of stimulus decr = increase intensity of light to see as long as total number of quanta (photon) is constant, and the area of the stimulus is below the critical diameter, the stimulus will be seen by the visual system due to spatial summation **Easier to see a faint light if it has a larger area, or tiny speck of light with a brighter glow*

Answer 29

spatial summation IA = C

Answer 30

- when duration of flash exceeds 100ms, temporal summation of scotopic system no longer occurs = must increase intensity of light in order for the pt to see - longer critical duration in scotopic system = greater sensitivity = poor resolution (multiple flashes of light are summed together within the time pixel - shorter critical duration in photopic system = poor sensitivity (less time for ganglion to absorb light) = excellent resolution (light summed over multiple pixels Summary - stimuli less than the critical duration = decrease intensity of flash to be seen - Decr duration of flash = incr intensity of stimulus to be seen as long as the photons are constant and duration of flash is below critical duration, the flash of light will be perceived by the visual system due to temporal summation *adding up small bits of information to make a bigger picture*

Answer 31

temporal summation (time) describes the relationship between the intensity and duration of stimulus that is below the threshold for temporal summation. It states that the number of quanta (photons) for a stimulus is below critical duration is constant It = C

Answer 32

Cone photoreceptors are MOST sensitive to light that strike orthogonal to the surface (will look brighter compared to other angles) Macular dz like ERM and ARMD may affect this

Answer 33

There are 3 types of cones: L,M,S that absorb different wavelengths - the absorption spectrum for each type of cone PR peaks at a different wavelength S = cyanolobe = 426 M = chlorolabe = 530 L = erythrolabe = 557 Rods = rhodopsin = 507

Answer 34

response of a cone PR to light is independent of the wavelength of light - wavelength only determines the probability of absorption of light by the cone PR - a single cone PR cannot discriminate between colors and intensity - color discrimination is based on the relative response of all 3 cones to a light with a given wavelength which is based on their absorption spectra

Answer 35

S cones, early stage glc pts show s cone VF loss on a b/y VF test even when complete VF loss is not readily apparent

Answer 36

2 visual stimuli that are physically different but appear identical b/c they elicit the same response in all 3 cone PR "colors made of different combinations of wavelengths but in our eyes it looks the same because our eyes cannot discriminate the different colors"

Answer 37

provides general rules for metamers 1. equal amounts of same wavelength of light are added to 2 metamers they will remain metamers 2. if the intensity of 2 metamers is increased or decreased by the same amt, they will remain metamers (but will appear brighter or dimmer than before) 3. stimuli A and B are metamers, stimuli B and C are metamers, then stimuli A and C are metamers

Answer 38

3 channels for color vision 1. R/G 2. B/Y 3. Brightness (mediated by rods) each channel treats 2 colors as opponents - if R/G channels stimulated by equal amts of red and green = no color or net response is 0, same with b/y channel

Answer 39

relative signals of each color channels ex. short wavelengths will signal red and blue = purple

Answer 40

normal color vision has 3 peaks 440nm, 520nm, 620nm these peaks DO NOT correspond to S,M,L cones. This is a result of color opponent processing of M and L cone inputs which shifts location of peaks in sensitivity spectrum

Answer 41

Hue = related to wavelength Saturation = desaturated color, colormetric purity Brightness = related to V function

Answer 42

used to quantify saturation high p value = highly saturated color p = L (luminance of pure wavelength/ L(Luminance of pure wavelength)+L(luminance of white light) p = L(l) / L(l)+L(w)

Answer 43

specifying color based on these 3 concepts: 1. hue 2. saturation 3. brightness

Answer 44

our perception of hue is associated with a given wavelength of light changes as the intensity of the light increases Ex. light wavelenghth of 540 appears green-yellowish, as the intensity of the light is increased it will look more yellow

Answer 45

colors appear the same under different lighting conditions

Answer 46

we can combine red (645), green (526), blue (444) light to create a stimulus that matches any other wavelength on the visible spectrum allows us to quantify how much of each primary color is needed to create another color

Answer 47

missing one of the three cone photopigments - Protanopes: missing erythrolabe (L cone), confused red orange green yellow, red colors appear dim (inherited) - Deuteranopes: missing chlorolabe (M cones), confused red orange green yellow, no dimming of red color (inherited) - Tritanopes: missing cyanolabe (S cones), confuse b/y (mostly acquired)

Answer 48

have all 3 photopigments but absorption spectrum of one of the photopigments is displaced Protanomalous trichromat: L cone (erythrolabe) is shifted towards the shorter wavelength, red orange green all appear green. REds appear dimmer (but not as strong as protanope), RED WEAK Deuteranomalous trichromat: M cone (chlorolabe) is shifted towards a longer wavelength, red orange green all look more red, GREEN WEAK

Answer 49

red tinted lenses that act as long pass filters, resulting in shift of cone PR absorption towards longer wavelenght. can be worn over one eye

Answer 50

how much we need to change a wavelength to perceive change of hue of the stimulus

Answer 51

540nm b/c only M (protanopes) or L (dueteranopes) cones are responding to light

Answer 52

495nm b/c only the M cones are responding to light

Answer 53

color confusion lines on a CIE are lines on the x-y plane along which all colors are indistinguishable. This is because only one cone photoreceptor is responding to the wavelengths of light along the color confusion line, resulting in poor color discrimination Alll color confusion lines originate from one point konwn as copunctal pt

Answer 54

must be conducted in daylight illumination or using macbeth illuminant C lamp in order for the results to be valid Ishihara plates = dx r/g defects HRR plates = dx b/y and r/g defects

Answer 55

- dichotomous test, consists of 15 colored chips dx r/g and b/y - useful for plaquenil testing

Answer 56

- dx r/g defects, CAN distinguish btw dichromats and anomalous trichromats

Answer 57

There's a test field (590nm) and mixture field (contains 670 and 546nm) that both can be adjusted - pt is instructed to adjust the ratio in the mixture field and the radiance of the test field until both fields appear identical - mixture field is adjusted from 0-73 (546-670nm) - the test field can be adjusted from 0-87 (very dim to very bright yellowish light) **3 wavelengths used all fall on the color confusion lines for protanopes and deuteranopes** Normal color vision = mixture scale to 45 and test scale to 17 (will appear yellow) Protanopes = mixture field set anywhere 0 - 73, - mixture field set 73 (670), test field will be low setting - mixture field set 0 (546), test field will be set high (DIMMING OF RED) Deuteranopes = mixture field set anywhere 0-73 - they will set test field to 17 regardless of the mixture field (NO DIMMING OF RED) Protanomalous trichromats = mixture field is set higher than normal b/c they are RED WEAK, they must add more 670nm light to the mixture field Deuteranomalous trichromats = adjust mixture field lower than normal, b/c they are GREEN WEAK, they must add more 546nm light to the mixture field

Answer 58

mixture field is higher than normal (45) protanomalous trichromat

Answer 59

deuteranope

Answer 60

dueteranomalous trichromat

Answer 61

Inherited (Genetic) - most commonly r/g defects - both eyes - does not change drastically over time - X-linked recessive Acquired defects - affect one eye more than the other - may change over time - b/y defect - equal frequency M & F

Answer 62

Outer retinal disease = b/y defects (ex. macular dz) inner retina, ON, or visual pathway dz = r/g defects (ex. optic neuritis)

Answer 63

rod monochromacy (only rods present) - greatly reduced VA and color discrimination

Answer 64

characterized by distortions of color but still able to discriminate color (ex. cataracts - acts as a yellow filter, after cataract sx objects appear more blue )

Answer 65

C = Lmax - Lavg / Lavg used to quantify our intuitive notion contrast Lmax = max luminance (white part of sine wave grating) Lavg = avg luminance of the grating Contrast ranges from 0-100

Answer 66

type of spatial modulation transfer function (SMTF) - describes how well a particular system (a lens) transfers contrast from the input (an object) to the output (an image - defocus lens = poor image contrast, particularly at higher spatial frequency more than moderate and low spatial frequency Summary ** the spatial contrast sensitivity function (CSF) describes how well our eyes can see patterns of different sizes and contrasts. It shows that we're best at seeing medium-sized patterns with moderate contrast. As patterns get either too small or too big, or if the contrast is too low, our ability to see them decreases. Understanding the CSF helps scientists and engineers design better images and displays that match how our eyes work.

Answer 67

600/CPD = snellen denominator

Answer 68

1. pt is shown sine wave grating of known frequency and very low contrast below the pts threshold (will see a uniform luminance NOT white and black stripes) 2. Pt increases the contrast grating until she can perceive sine wave grating (CSF is the reciprocal of threshold value) 3. the procedure is repeated for sine-wave gratings of different frequencies in order to generate the entire CSF

Answer 69

there is a limit to our ability to resolve fine spatial details - high frequency cut off represents the pts measured VA 1. optical limitation (aberration still occurs with perfect focus) 2. The density of photoreceptors is finite, thus our ability to resolve spatial detail is physically limited by the spacing of the PR

Answer 70

Bright b/c cone PR are primarily responbile for high contrast VA

Answer 71

High - even at high contrast, very small letters cannot be resolved by the visual system

Answer 72

represents the angle (measured from the eye) btw 2 bars that are just resolvable. MAR is related to the snellen fraction SF (snellen fraction) = 1/MAR 60 arc minutes = 1 degree

Answer 73

600/15 = 40 20/40

Answer 74

CPD/30 = snellen fraction reduced form

Answer 75

1. lateral inhibition in the retina 2. ganglion cells in the retina shows a center-surround receptive field - stimuli that falls in the center will excite the cell - stimuli that falls outside the center will inhibit the cell - a large stimulus falls on the peripheral part of the receptive field, resulting in inhibition of the cell, thus limiting our VA at low spatial frequencies

Answer 76

simple idea of mathematics that says any fucntion can be broken down into a sum of sines and cosines - visual system works similar to fourier analyzer - visual system can break down almost any visual scene into its individual pixels and analyze each pixel separately and then resemble the pixels to create a complex visual scene Summary ** Fourier analysis of the visual system is a way of breaking down images into simpler components called spatial frequencies. It's like taking a complex picture and breaking it into basic patterns of different sizes. These patterns are akin to the building blocks of the image.

Answer 77

- strip of gradual change in luminance from one end to the other - instead of perceiving a gradual luminance change, the pt perceives a light and dark band - Mach bands occur b/c the gradual change in luminance along the strip is difficult to perceive due to its very low frequency mach bands provide evidence of fourier analyses in the visual system Summary ** Mach bands are a visual illusion that makes edges between light and dark areas appear even sharper than they really are. When you look at a transition between a light area and a dark area, such as where a shadow meets a lit surface, you might notice that the edge looks darker on the light side and lighter on the dark side. It's like a little halo of brightness or darkness right at the edge. This effect happens because of how our eyes and brains process contrast. When there's a sudden change in brightness, our visual system amplifies the contrast to help us see the difference more clearly. Mach bands are an exaggerated version of this phenomenon. They occur because our eyes and brain enhance the contrast at the edge, making it appear even more distinct than it really is. This can help us perceive objects and edges more sharply, even in low-contrast situations.

Answer 78

- Monocular - Binocular

Answer 79

Pictorial depth cues (STAL) - angles - lighting - texture - shadows Motion parallax = relative mvmt btw objects provides clues about positional relationship btw the objects

Answer 80

comparison of location of the image formed on each retina Uncrossed retinal disparity - image falls on nasal side of each fovea = objects perceived to be farther away Crossed retinal disparity - image falls on temporal side of the retina = objects perceived to be closer

Answer 81

INSIDE panums fusional area = stereopsis OUTSIDE panums fusional area = diplopia

Answer 82

object appear to be moving (not true motion) (ex. Christmas tree lights) Beta mvmt = if T (time interval) is chosen properly, spot of light will appear to be moving No motion - if T is very small or very large Phi mvmt = T is slightly too large or too small, the pt will perceive partial motion

Answer 83

motion V5/MT primarily responsible for motion detection - cells in V5 respond to global stimuli (ex. random dot kinematograms). - electrically stimulating this area will alter the perception of motion (in monkeys)

Answer 84

stimulus that contains randomly moving dots - we can use this to measure percept of motion by change direction and mvmt of dots or by measuring how far the dots must move in order for a pt to perceive motion (minimum/max displacement thresholds)

Answer 85

- percept of motion lingers after the stimulus of motion is removed, the perceived motion moves in the OPPOSITE direction (ex. waterfall illusion)

Answer 86

- located in V5 - some are excited w/ upward mvmt and some downard mvmt - stimulus appears stationary when opponent detector cells respond equally - When a pt views a waterfall - downward motion detector cells are excited, after prolonged exposure, the downward motion detector cells adapt and become less sensitive - when a pt views a stationary object, the waterfall will appear to move upwards b.c the upward motion detector cells are responding at a higher rate

Answer 87

60-80 degrees/sec

Answer 88

similar to spatial perception but now dealing w/ changes in visual scenes over time (change in luminance over time) - often measured with a flickering stimulus (similar to sine wave grating) - change in luminance in space

Answer 89

similar to SMTF from spatial vision - based on percentage modulation for a flickering stimulus with a given frequency - plot sensitivity at different temporal frequencies (plot looks similar to CSF, with a high and low frequency cut off)

Answer 90

form of "temporal" contrast Pm = 100 x A/Lavg A = amplitude of stimulus Lavg = time-averaged luminance Pm = percentage modulation

Answer 91

- our vision cannot detect very slow temporal change, we cannot watch the grass grow b/c the change happens on a very slow time scale (ex. we cant see grass grow) Ex. Purkinje Tree, Troxler phenomenon

Answer 92

shine a light on our closed eyelid, we'll be able to make out the structure of the retinal vessels b/c the light results in higher frequency changes in the images on our retina

Answer 93

our visual system has poor sensitivity for very low-frequency stimuli b/c of lateral inhibition in the retina, thus if we continuously stare at an object it will eventually fade away. to combat this our eyes continuously move during fixation, this results in temporal changes in retinal illumination that exceed threshold so the object will remain visible

Answer 94

- our visual system has a high frequency cut off - frequency that can be resolved at max modulation - because neurons take a finite, nonzero time to respond to stimuli and therefore time "pixels" are not infinitesimally small **smallest details that our eyes can distinguish**

Answer 95

Above CFF = perceive constant light Below CFF = perceive flickering light

Answer 96

Above CFF = the light will appear constant

Answer 97

Ferry-Porter Law Granit-Harper Law Broca-Sulzer Effect Brucke-Bartley Effect Talbot-Plateau Law

Answer 98

High frequency CFF scales linearly with log of retinal illumination this is likely b/c the response of the retina speeds up following increased light adaptation

Answer 99

the high-frequency CFF increases as the stimulus area is increased; this is because the peripheral retina (larger time pixels) is better at detecting flicker than the central retina

Answer 100

Light flashes above the threshold appear brightest when they last for 50-100msec. Longer or shorter flashes of light with the same intensity appear dimmer

Answer 101

flickering light appears brighter than a steady light of the same avg luminance (Lavg)

Answer 102

Stimulus that is flickering at a frequency greater than the CFF (appears constant) appears equally bright as a non-flickering stimulus with a luminance equal to the time-avg luminance of the flickering stimulus

Answer 103

Forward masking: mask is presented before the target Backward masking: mask is presented after the target Paracontrast: maks first and target 2nd, with both being close to each other in space Metacontrast: target first, mask second, with both being close to each other in space Simultaneous masking: mask and target appear at the same time

Answer 104

simultaneous masking - explains why pts often have a better VA when they are shown single letters instead of lines of letters

Answer 105

visual phenomena that originate from the eye itself

Answer 106

Light reflects off the front and back surface of the lens and cornea, forming unintended "ghost image" I = anterior cornea, virtual/upright/small, very bright (reflection) II = posterior cornea, virtual/upright/very small, bright (reflection and refraction) III = Anterior lens, virtual/upright/large, dim IV = posterior lens, real/inverted/smallest, very dim I-III = created from convex surface IV = concave surface (that's why its unique)

Answer 107

I > II > III > IV Image III moves forward, image IV moves backward (toward the retina)

Answer 108

Retinal break or detachment, vitreous syneresis and traction - vertical streaks or flashes of light in the peripheral VF

Answer 109

pt ability to perceive retinal blood vessels if we shine a moving light on the retina

Answer 110

due to birefringence of the radial Henle's fiber layer in the macula - used to diagnose eccentric fixation - pt stares at a blue object through a rotating polaroid, she will perceive a rotating yellow brush centered around point of fixation - if pt uses eccentric fixation, he will see a haidingers brush centered on a point other than the fixation target

Answer 111

- based on fact that blue wavelengths of light are primarily absorbed by pigment within the macula rather than the cone photoreceptors - If pt fixates a purple light (composed of blue and red wavelengths), he will perceive a red spot located at the point of fixation b/c all of the blue light has been absorbed by the macular pigment - maxwell's spot can also be used to dx eccentric fixation - if pt has eccentric fixation, red spot will be located away from the point of fixation

Answer 112

1. Maxwell's spot 2. Haidinger's brush

Answer 113

flash of light due to mechanical or electrical stimulation of the retina, or 2' to neural noise ex. eye rubbing

Answer 114

- most commonly seen when a pts views a dim light in a dark room - blue arcs will originate form the source of light and extend towards the physiological blind spot

Answer 115

Parvocellular pathway: detection of detail and color, associated with object size/shape/details. includes neurons in central retina that are sensitive to high spatial frequencies (CONES) Magnocellular pathway: detection of motion, includes peripheral retinal neurons that are sensitive to low spatial frequencies (RODS)

Answer 116

Magnocellular vision is suppressed just before, during, and after a saccadic eye mvmt to prevent blurring of an image

Visual Perception Flashcards

(146 cards)