VOP - The Light Sense II - Topic 3 Flashcards
Define the term increment threshold.
The increment threshold is the smallest amount of energy which must added to a stimulus in order to detect a change in the stimulus.
How do we calculate increment threshold (JND
)?
Δ𝐿= k x 𝐿𝑏
ΔL = increment threshold (JND) Lb = background luminance K = Weber’s constant (or fraction)
What is Weber’s Law?
jnd (ΔL) is directly proportional to the background Luminance
Δ𝐿/𝐿_𝑏 =𝑘
Describe the essential parts of the tvi curve in photopic vision.
- Log threshold intensity is plotted against background luminance.
- At high background luminances, cones determine the threshold
- At low luminances rods are the determining factor.
What does ‘tvi’ curve stand for?
threshold vs intensity curve
What is the Effect of stimulus size on increment threshold?
as the stimulus size increases, the ability to detect the stimulus improves (threshold gets smaller).
What is the jnd threshold equal to for small stimuli sizes?
For small stimuli sizes, the jnd threshold, ΔL, is inversely proportional to the area of the stimulus.
What is Ricco’s Law?
the luminance of the increment required for detection, decreases as the size of the spot increases – up to a certain critical point (Ricco’s Area).
What is spatial summation?
two stimuli falling on nearby areas of the retina add their effects; though either alone may be inadequate to evoke the sensation of light, they may do so when presented simultaneously.
Define Ricco’s Area and what it represents
is the largest area for which complete spatial summation occurs
-represents the underlying pooling
What is ricco’s area in the fovea?
5 min arc
When does Ricco’s area become larger?
At peripheral retinal locations
-indicating greater pooling of retinal signals
