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70 Cards in this Set
- Front
- Back
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Ascending Limits?
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Steadily Increasing stimulus`
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Descending Limits?
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Steadily decreasing stimulus
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What is a psychometric function?
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Plot of percent correct vs variable of interest
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Method of Constant Stimuli?
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Randomized stimulus
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Automated VF testing uses what method?
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Stairstep Method (gradual increase then decrease to refine threshold)
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Which method eliminates method of individual threshold criteria?
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Forced Choice Method
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How do you define the threshold in FCM?
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Halfway between chance and perfect
Two choices - 75% (50%-100%) |
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What method is used in determining Dark Adaptation Curve?
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Ascending Limits - because it starts very low intensity
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What is the Signal Detection Theory?
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Mathematical basis for how to decipher noise from a signal
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SDT: Define Detectability?
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If a signal is low and noise is high, there distributions will overlap, and D will be very low
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Describe Lax Criteria?
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We click the button alot.
Leads to false + But we never miss a signal (High Sensitivity) |
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Describe Strict Criteria?
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We are cautious, dont click alot
Leads to false - But we never guess a signal is there when it isnt (High Specificity) |
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Describe Sensitivity?
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Chance a test gives a + result, when a + result is actually present
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Describe Specificity?
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Chance a test gives a - result, when a - result is actually present
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False Negative Rate?
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1 - sensitivity
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False Positive Rate
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1 - specificity
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Positive Predictive Value?
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True Positives / Any Positive Result
(I Test positive for AIDS, now what are the chances I have AIDS) |
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Negative Predictive Value?
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True Negative / Any Negative Result
(I Test negative for AIDS, now what are the chances I do not have AIDS) |
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Receiver Operating Curve
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Hits vs False +.
Lax - upper right Strict - lower left |
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Radiometry vs Photometry?
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Radiometry deals with physical properties that are easy to measure. Photometry deals with how our visual systems deal with electromagnetic. So it is how we respond to light
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Radiant Power vs Luminous Power
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RP - energy per second made by a light source (WATTS)
LP - based on response, if a source elicits a greater response, its LP is greater (LUMENS) |
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Luminous Efficiency Function
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Scotopic (Rods): For every watt of power from a light source @ 555 nm, the visual system responds with 680 lumens
Photopic (Cones): @507, 1700 lumens |
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Radiant Intensity vs Luminous Intensity?
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RI - RP in a given direction. (W/angle)
LI - LP in a given direction. (candela, L/Angle) |
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Radiance vs Luminance?
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Rad - Intensity per area of source
Lum - Intensity per area of source How mush light power does a source of certain size make? |
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Irradiance vs Illuminance?
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Irrad - how much light (power) reaches a target
Illum - how much light (power) reaches a target |
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Find the luminous power of 10 W source if:
V=0.5 @ 600 nm and V=0.2 @ 500 nm |
(0.5)(680) = 340 lumens/watt
(0.2)(680) = 136 lumens/watt x 10 =3400 lumens =1360 lumens Note this is for photopic (cone), scotopic we use 1700 I/W |
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What is Abneys Law of Additivity?
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3400 + 1600 = 4760 lumens
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What is the effect of a Neutral Density Filter?
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Decrease overall stimulus magnitude
CW = Over left CCW = Over right |
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Lambert Surface?
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A surface that shows the same illuminance from every viewing angle.
Lum = Reflectance x Illuminance (linear relationship) |
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What is the opposite of a Lambert Surface?
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Specular Surface.
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What is Retinal Illumination, and what is it measured in?
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Amount of light that falls on the retina.
Measured in Trolands T = LA (A=area of pupil) |
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Describe the sensitivity of the Scotopic (Rod) system?
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Think about darkness, you need to be supersensitive to any light.
Your threshold (standards) are low, you will take whatever |
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Describe the sensitivity of the Photopic (Cone) system?
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You are concerned with detail. You want lots of light.
Your threshold (standards) are high, you need alot of light to decipher detail. |
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What equation tells us that dark adaptation is not solely related to rod regeneration?
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Dowling-Rushton.
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What is Rico's Law?
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Spatial Summation. Stimuli smaller then critical diameter are only seen as one stimuli.
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Which system has a larger critical diameter?
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Scotopic system sees less detail, so critical diameter is larger.
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What is Bloch's Law?
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Temporal Summation. States that there is a critical duration that everything below it is summed.
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What is the critical duration for scotopic (rod) system?
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100 ms, everything under this is summed
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What is the critical duration for photopic (cone) system?
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10 ms, everything under this is summed
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When does Stiles Crawford come into play?
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Seen in cone system only, orthogonal hits are seen as brighter
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Describe Hue?
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Our perception of color.
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Describe Saturation?
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How much white a color has
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What is Bezold Brucke Phenomenon?
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Hue and brightness are related. Hue changes for a specific wavelength as intensity increases
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What is color constancy?
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Our brains adapt and see colors the same even under difference lighting conditions.
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What inheritance pattarn does R/G Defects have?
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X-Linked
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Outer retinal diseases have what defect?
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Blue/Yellow
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Inner retinal diseases/ONH/VP have what defect?
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Red/Green
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What are Chromatopsias?
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distortion of color, but not defect
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What equation do we juse to determine contrast?
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Lmax - Lavg
___________ Lavg |
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What is SMTF?
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Spatial Modulation Transfer Function
how a high contrast image is changed after passing thru a lens Cimage _______ Coriginal object |
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SMTF:
A poor focused lens effects what frequencies? |
Higher frequencies more then moderate
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Contrast Sensitivity Function?
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SMTF for humans.
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High Frequency Cutoff
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Limit to resolvable spatial detail.
1. Optical Limitations 2. Density of PR is finite Higher under photopic (cone) because VA is better w/bright light |
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Low Frequency Cutoff
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1. Lateral Inhibition
2. Gang Cells: center surround |
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High freq cutoff is 15 cycles, what is VA?
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15/30, divide by 30
20/40 |
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Fourier Analysis?
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A function can be broken down into sum of its components.
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Mach Bands?
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Suggest our visual system is performing a Fourier analysis into individual frequency components and handling them separately
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Which two regions are most associated with motion detection?
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V5
MT |
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Purkinje Tree?
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We do not see our retinal vessals because lateral inhibition blanks them out. But shining a light on the retina creates high freq changes in our retina (by using shadows).
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Troxler Phenonmenon?
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Lateral Inhibition in the retina leads to poor sensitivity for very low freq stimuli. We use microsaccades to create temporal changes in retinal illumination to exceed threshold
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Ferry Porter Law?
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As retinal illumination increases so does CFF
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Granit Harper Law?
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As Stiumlus area increased, so is CFF.
Why? - peripheral retina is better at detecting flicker |
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Broca Sulzer Effect?
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light flashes bt 50-100ms are brighter then any other
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Brucke Bartley Effect?
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Flickering light appears brighter then steady light with same average luminance
(BELOW CFF, flicker is brighter then steady of same avg) |
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Talbot Plateau Law
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Above CFF, flicker and steady light with same average are seen as the same brightness
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Forward Masking?
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mask precedes target
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Backward Masking?
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mask after target
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Paracontrast?
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mask first, target second, close in space
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Metacontrast?
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target first, mask second, close in space
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Simultaneous Masking?
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more noticeable in amblyopia
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