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10 Cards in this Set

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  • Back
Ricco's Law
-Spatial Summation @ Fovea.
-ONLY applies to stimuli less than 10 min of arc.
-Luminance X Area= Constant absolute threshold.
- Increase luminance of stimulus, can have a smaller stimulus and still maintain threshold.
- Increase Area of stimulus, you can decrease luminance of stimulus and keep same threshold.
-Receptive field= region of retina when stimulated by light. There is convergence, overlapping a,d divergence, which influences firing rate of cell.
Piper-s Law
Spatial summation NOT at fovea, but rather between fovea and 10 degrees away.
- Lunminance X Area (to the 1/2 power)= Constant threshold
Pieron's Law
Spatial summation NOT at fovea, but rather beyond 10 degrees from fovea.
- Luminance X Area (to the 1/3 power)= Constant threshold.
Not a complete summation.
Bloch's Law
-TEMPORAL summation less than 100 ms.
-Luminance X time= Constant threshold
- If time of stimulus is increased, you can decrease luminance and maintain cosntant threshold.
100 ms describes realtionship to PERIPHERY.
10 ms relation to center of FOVEA. -Increase time by 2, decrease luminance by 2.
Weber's Law
Used in measing threshold of a flsh stimulus on an illuminated background, with either the background or stimulus changing in illumination.
- Want to know how much more additional light to the background is needed for the spot to be seen.
- Weber's Law, more simply stated, says that the size of the just noticeable difference (i.e., delta I) is a constant proportion of the original stimulus value. For example: Suppose that you presented two spots of light each with an intensity of 100 units to an observer. Then you asked the observer to increase the intensity of one of the spots until it was just noticeably brighter than the other. If the brightness needed to yield the just noticeable difference was 110 then the observer's difference threshold would be 10 units (i.e., delta I =110 - 100 = 10). The Weber fraction equivalent for this difference threshold would be 0.1 (delta I/I = 10/100 = 0.1). Using Weber's Law, one could now predict the size of the observer's difference threshold for a light spot of any other intensity value (so long as it was not extremely dim or extremely bright). That is, if the Weber fraction for discriminating changes in stimulus brightness is a constant proportion equal to 0.1 then the size of the just noticeable difference for a spot having an intensity of 1000 would be 100 (i.e., 0.1 X 1000 = 100).
Weber-Fechner Law
Law applies only when Weber's law depicts a flat curve and the ration of change in illumination/illumination if constant, The law breaks down at very low and very high backfround luminance.
( Weber law info: n one of his classic experiments, Weber gradually increased the weight that a blindfolded man was holding and asked him to respond when he first felt the increase. Weber found that the response was proportional to a relative increase in the weight. That is to say, if the weight is 1 kg, an increase of a few grams will not be noticed. Rather, when the mass is increased by a certain factor, an increase in weight is perceived. If the mass is doubled, the threshold is also doubled.)
Devries-Rose Law
Change in illumination= Illuniation to the 1/2 power. Increment change is equal to the sqaure root of the background.
Michelson contrast
Contrast= (Luminance max (of wihte)- Luminance min (of black))/ (Luminance max +Luminance min)
Troxler phenomenon
Image motion on retina will give you continuous visual perception of the real world, no matter how small. Comare box with fuzzy eduges to one with sharp ones. The shar box will stay sharp and contrast will stay same. Box with fuzzy border will show change in contrast.
Ferry-Porter Law
As illumination is increased, Critical flicker frequency is increased. CFF= a constant X log of Intsensity of fluckering stimulus.
- ONLY applies to linear function regions. There is a certain frequency where you can no longer make out the flicker of a stimulus, and it appears as only 1 steady light.