Equations for Sensation and
Perception
Linear
Interpolation for determining threshold:
Method of Constant Stimuli
Threshold=
|
(50%-Lower%)*
|
(UpperVal-LowerVal)
(Upper%-Lower%)
|
+LowerVal
|
Forced-Choice Method
Threshold=
|
(75%-Lower%)*
|
(UpperVal-LowerVal)
(Upper%-Lower%)
|
+LowerVal
|
Calculations
Related to Measurements of Visual Intensity:
Reflectance =
|
Luminance
Illuminance
|
Contrast Ratio=
|
Luminance_Max
Luminance_Min
|
Calculation of
Dioptric Power of a Lens:
Diopters (D) =
|
1
Focal Distance (m)
|
Weber's Law
Fechner's
Law
S=klog(I)
Steven's Power
Law
S=cIb
Reflectance
Reflectance =
|
Luminance
Illuminance
|
Contrast Ratio
CR =
|
Lmax
_____________
Lmin
|
Conversion from Cycles/Screen to Cycles/Deg
- Step 1 Develop Conversion Ratio (CR):
- CR = (Known Cycles/deg)/(Known Cycles/Screen)
- e.g. for the demonstration in class: standard = 3
cycles/deg & setting 128 cycles/screen on my monitor
- CR = 3/128
- Step 2: Conversion
- Multiply your mean results by this value.
- You can only do those results from a given screen.
If you change monitors, you will need a new CR for the screen values from
that monitor.
Calculating Perceived Distance
Relative Distance = (ViewingDistance*Disparity)/InterpupillaryDistance
(all units should be mm)
Actual Distance = ViewingDistance-RelativeDistance
Size Constancy
Both of the following equations hold simultaneously:
Sr α 1/dp
Sp ~= k
Emmert's Law
Both of the following equations hold simultaneously:
Sr = k
Sp α dp
Calculation of decibels