visual perception 2 NBEO.txt
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How are sensitivity and threshold related?
What subjective testing methods test threshold?
- Method of ascending limits
- Method of constant stimuli
- Stairstep method
- Adjustment method
What method is exploited in automated visual testing?
What semi-subjective methods test threshold?
- Forced choice
- Signal detection
What is the size of resolution acuity?
30 sec arc
What is the size of detection acuity?
1 sec arc
What is the size of vernier acuity?
3 sec arc
What is radiometry?
Measurement of energy per time
What does a watt represent?
- Energy per second produced by a light source
- 1 joule/second
What is radiant intensity?
- Energy per second in a given direction
- Watts per steradian
What is radiance?
Intensity per projected area of source
What is irradiance?
- Amount of radiant power per unit area of surface
- Amount of radiant power that hits an object
What units are included in radiometry?
- Radiant power
- Radiant intensity
What units are included in photometry?
- Luminous power
- Luminous intensity
What is luminous power?
- Total power produced by a light source in all directions
What is luminous intensity?
- Luminance power in a given direction
- Lumens per steradian = candela
What is luminance?
- Amount of light leaving a surface in a specific direction
- Candela per square meter = nit
How many nits are there in 1 foot-lambert?
What is illuminance?
- Power falling on a surface in all directions
- Lumens per square meter = lux
How many lux are there in 1 foot-candle?
What are narrow band filters?
Allow only a small range of wavelengths to pass through
What are interference filters?
Transmit only one wavelength
What are broad band filters?
Transmit large range of wavelengths
What are long-pass filters?
Transmit only long wavelengths
How do sunglasses filter UVR?
By use of long-pass filters
What are neutral density filters?
The transmit wavelengths equally at different intensities
What happens if a neutral density filter is placed over the right eye?
The planar pendulum appears elliptical and moves in a counterclockwise direction
What happens if a neutral density filter is placed over the left eye?
The planar pendulum appears elliptical and moves in a clockwise direction
What percentage of rods need to be bleached in order to saturate?
What are metamers?
Two visual stimuli which are physically different, but appear identical
What nanometer is most sensitive in S cones?
What nanometer is most sensitive in M cones?
What nanometer is most sensitive in L cones?
What nanometer is most sensitive for rods?
What is the Bezold-Bruke phenomenon?
Wavelengths show a slight change in hue as the intensity of light is increased
What is the copunctal point?
Where colors are indistinguishable on a CIE color system
How do you calculate contrast?
- Example problem
- Projected luminance 50 units
- Onto a background of 100 units
- Contrast = (50-100) / (50+100) = 50/150 = 33 percent
What are monocular clues in depth perception?
- Pictoral depth
- Motion parallax
What are binocular clues in depth perception?
- Uncrossed retinal disparity
- Crossed retinal disparity
What is uncrossed retinal disparity?
If the image falls on the nasal side of the retina, the object is perceived to be farther away
What is crossed retinal disparity?
If the image falls on the temporal side of the retinal, the object is perceived to be closer
What is the Troxler phenomenon?
The fading of retinal images that are stabilized
What is the broca-sulzer effect?
Light appears brightest when they last for about 50-100msec
What is the bruke-bartley effect?
Flicker light of the same luminance appears brighter than steady light
What is masking?
When one stimulus (mask) decreases the visibility of another stimulus
What is forward/backward masking?
Mask proceeds/follows the target
What is paracontrast masking?
Mask appears first and target appears second
What is metacontrast?
Target appears first and then the mask second
What does the parvo pathway detect?
Detail color, and object size
What does the magno pathway detect?
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