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50 Cards in this Set
- Front
- Back
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What methods does visual fields use?
ascending limit descending limit constant stimuli stairstep method |
stairstep
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In signal detection theory, what does detectability respresent with regard to signal and noise?
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Ability to distinguish between noise and signal + noise (sensitivity).
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What is sensitivity and specificity?
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Sensitivity = true positive (+=+)
-ie. These people have the dz -For a percentage, divide true positives by total people who have dz (true pos + false neg) Specificity = true negative (-=-) -ie. These people don't have dz |
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What is a type 1 error?
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False positive
ie. 1 boy crying wolf |
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What is a type 2 error?
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False negative
ie. excessive skepticism |
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What is the null hypothesis?
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No relationship exists between 2 things. Theory that is put forward to be tested.
Example: There is no difference between new drug and old drug Result: Reject H0 in favour of H1, or alt hyp (there is a difference; ie. our drug is different!). "Do not reject H0" doesn't mean H0 is true, just that we couldn't prove it wrong. |
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What is the alternate hypothesis?
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There is a difference
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What is probability value (p-value)?
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Probability of getting a result more often than if by chance alone.
Small p-values less than the set statistical significance (p<0.05 or 0.01, or less than 5 or 1%) suggest that the results are statistically significant (reject null hypothesis). |
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How does strict criteria affect detection theory (false/true positive/negative)
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Fewer hits, low false positives.
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How does lax criteria affect detection theory (false/true positive/negative)
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High hits, high false positives. Rarely miss a signal that's actually present.
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Difference between radiometry and photometry?
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Radiometry = energy per time of light (electromagnetic radiation; W)
Photometry = how our visual system responds to light (lumens). |
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Our visual system is most responsive to what wavelength in photopic conditions?
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555 nm produces 680 lumens/watt
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Our visual system is most responsive to what wavelength in scotopic conditions?
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507 nm produces 1700 lumens/watt
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Illuminance vs luminance?
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Illuminance deals with light falling upon a target object (like irradiance but not a measureable quantity; deals w/ our visual system), measured in foot-candles
Luminance deals with luminous power of source (ie light bulb; like radiance), measured in foot-lamberts |
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What do neutral density filters do?
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Reduce all wavelengths equally, thus slowing neural response. Over left eye = pendulum rotates clockwise. Due to Pulfrich phenomenon (ND filter slows down response due to decr illumination in that eye).
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Describe affects of changing illuminance, area, and distance exposed to incident light.
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Triple illuminance = triple luminance.
Triple diameter = increase incident light by factor of 9. Double distance = 1/4 illuminance. |
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Where is the photochromatic interval (difference between scotopic and photopic sensitivies) 0?
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650 nm. Here, photopic and scotopic sensitivities are equal. No rod-cone break is present here.
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What happens to longer wavelengths as illumination increases (Purkinje shift)?
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Appear brighter (shifting from scotopic, peak sensitivity 507 nm, to photopic, 555 nm).
Trick: at night, rods dominate and are best at blue. Everything looks blue at night and we are basically color blind. During the day, we can see red roses better. |
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What happens with threshold after dark adapting
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Decreases (more sensitive). The pigment becomes unbleached (regenerates) and is ready to absorb photons.
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How many rhodopsin molecules must be bleached for rods to become saturated?
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10 %. That is enough to open the critical number of Na+ channels. Cones don't saturate.
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What does Ricco's Law vary when testing sensitivity?
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Area and intensity at each given area. Increase area by factor of 3, threshold intensity decreases to 1/9.
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What does Bloch's Law vary when testing sensitivity (resolution)?
Which has larger critical duration (less sensitive to flashing light), scotopic or photopic? |
Time (temporal summation).
Time pixels are larger in scotopic vision (can't see quick flashes) |
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What is Stiles-Crawford effect?
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Light hitting orthogonal (straight down) to cones is much brighter.
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Photoreceptor pigment and wavelength
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S cones - cyanolabe - 440 nm (affected by dz quicker, ie glaucoma)
M cones - chlorolabe - 534 nm L cones - erythrolabe - 564 nm Rods - rhodopsin - 498 nm |
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What are the following missing?
Protanope Deuteranope Tritanope |
Red (L cone, erythrolabe)
Green (M cone, chlorolabe) Blue/yellow (S cone, cyanolabe) |
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What are hue and saturation?
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Hue is color (wavelength) and desaturation means it becomes closer to white. As brightness increases, our perception of hue changes.
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What is the CIE diagram?
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Helps determine the resulting color of 2 color mixtures. Draw a line connecting the two, make a point on the line closer to the color with higher amount, connect that point to the central "white" mark and extend to find resultant color.
Bottom left starts w/blue, point is green, right is red. |
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Protanopia:
-Dimming of colors? -inher/cong? -how is spectrum shifted? |
-Dimming of colors involving R/G
-Inherited -L cone spectrum shifted to shorter wavelengths (look greener) |
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Deuteranopia:
-Dimming of colors? -inher/cong? -how is spectrum shifted? |
-NO dimming of colors
-Inherited -M cone spectrum shifted to longer wavelengths (look more red) |
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What does the X-chrom contact lens do?
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Help overcome R/G color deficiencies (it's red; it shifts color towards red)
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Under what lighting do you do color testing?
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Daylight or Macbeth Illuminant C lamp
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What does the Farnsworth D-15 test assess?
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Diagnoses all 3 (protan, deutan, tritan), but cannot distinguish between dichromats and anomalous trichromats (both R/G defects).
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What does the Nagel Anomaloscope test?
Describe the findings w/each color deficiency. |
Distinguish dichromacy and anomalous trichromacy in R/G defects.
-Dichromat (prot/deut) perceive match w/test stimulus along the confusion line (mixture field), but prot increase the intensity while deut don't) -Protanomalous trichromat - red-weak (must increase intensity of red to achieve match) -Deuteranomalous trichromat - green-weak If patient can't match, then he's anomalous! |
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1) What color do cataracts affect?
2) What color does outer retinal dz affect? 3) What color does inner retinal, opt nerve, visual pathway problems affect? |
1) yellow filter blocks blue light
2) B/Y 3) R/G |
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What is the peak sensitivity for human contrast sensitivity function (the top of the CSF curve)?
What is the high SF cutoff? |
Peak: 4 cycles/degree.
Cutoff: 40-60 cyc/degree. |
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1) What limits our CSF high frequency cutoff?
2) What limits our CSF low frequency cutoff? |
1) optical limitations, density of photoreceptors
2) Lateral inhibition from ganglion cells (center surround) |
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What is MAR in relation to:
-The eye -20/20 Snellen E |
-MAR = Minimum Angle of Resolution = inverse of Snellen = represents the angle (as measured from the eye) between 2 just resolvable points
-Ea 1 of the 5 bars of the Snellen E=1 arcmin -1 cycle = 2 arc minutes |
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What does 20/40 mean w/Snellen and MAR?
(p. 188 Schwartz) Conversion of: -Snellen to Arcmin -MAR (arcmin) to degrees, cycles/degree, Snellen |
The measurement was taken at 20 ft, the smallest optotype the pt can read subtends 5 arcmin @ 40 ft, the details of this optotype subtend 1 arcmin @ 40 ft, and the pt's MAR is 2 arcmin
-20/40 = 2 arcmin (MAR) -1 arcmin = 1/60 degree = 30 cyc/degree = inverse Snellen |
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Shortcut to converting snellen to cycles/degree and MAR
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MAR (arcmin) is the inverse of Snellen
Divide 600 by cyc/degree to get Snellen eg. 4 cyc/degree to Snellen 600/4=150=20/150 Snellen eg. 20/150 to cyc/degree 600/150 = 4 cyc/degree |
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How many cycles/degree can a typical adult see?
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40-60 cycles/degree (MAR = 0.75)
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What is uncrossed retinal disparity?
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Object is beyond fixation, falling on nasal retina.
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What pathway processes motion, and what area does it end up in?
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-Magno pathway
-V5 (temporal area, MT) |
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What happens in motion aftereffects?
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After watching motion, such as waterfall, you become less sensitive to it and when stopped, the stimuli appears to move in opposite direction.
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Bezold Brucke phenomenon
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Perceived hue is closely tied with the luminance of an object, and increasing the luminance will alter a person's perception of hue. The phenomenon goes by the name Bezold Brucke.
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Photopic system critical duration?
Scotopic? |
Photopic: 10 msec
Scotopic: 100 msec With a stimulus shorter than these numbers, threshold changes linearly w/flash duration. If stimulus is longer, it almost changes linearly (just slightly less than) |
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Broca Sulzer effect
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The Broca-Sulzer effect says that light flashes of duration 50-100 msec appear brighter than flashes of other durations. That is, there is a peak in the perceived brightness vs. duration curve, and the peak occurs at t approximately 50-100 msec.
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How long does it take for cones to dark adapt (ie rod-cone break on adaptation curve)?
Rods? |
Cones: 10 min
Rods: 30-40 min |
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Describe inheritance of R/G defect
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X-linked recessive.
If dad has it and mom is carrier, son has 50% chance of getting it. Daughter either has it or is a carrier. |
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Weber's Law
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Weber's law says that the increment threshold is directly proportional to background intensity (or luminance) under photopic vision (see Region E of the light adaptation curve).
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Review all the laws at the end of the chapter (p.238)
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Ferry-Porter
etc |
