2.04 temporal vision Flashcards
What is temporal vision
stimuli that change over time
what are the two types of temporal variations
- temporal flash
- temporal flicker
what is temporal flash
- When the luminance increases to a maximum and then decreases to its starting level over a brief duration
- you must specify the background luminance, change in luminance or maximum luminance in order to describe the stimulus
- flash duration specified in seconds or milliseconds
What is temporal flicker
- to describe this stimulus, one must specify its average luminance, temporal contrast and its temporal frequency
How do you work out the amplitude
lmax-lmin/2
What is the effect on the neurons response when the temporal frequency is high vs low
when low = response is modulated and reflects stimulus presented
when high = response is steady and no longer represents the stimulus presented. Neurons not fast enough to resolve the stimulus and the visual system perceives a steady stimulus.
what is the critical flicker frequency
the flicker rate for which the stimulus appears to flicker 50% of the time and appears fused 50% of the time
what is the Broca-Sulzer effect
the perceived brightness of a suprathreshold flash depending on its duration
what is the Talbot-Plateau law
The brightness of the flickered stimulus will equal that of the steady light with luminance matching the average luminance of the flickered stimulus
Frequency > CFF (steady) exhibits Talbot plateau law
Frequency<CFF (flickering) exhibits the Brucke-Bartley effect
what is the Ferry-Porter law
The effect of luminance on CFF
CFF=klogL + B
L = retinal illuminance
k and b are constants
Increasing retinal illuminance (units Trolands) increases the sensitivity to high temporal frequencies and increases the CFF
What is the Granit-Harper law
Effect of area on CFF
CFF= klogA + b
A = stimulus area
k and b are constants
where in the vision is flicker more noticeable
in peripheral vision
how to work out temporal frequency flicker
add both ON and OFF to get one cycle
then convert ms to seconds and then do 1/seconds to work out how many cycles would be in 1 second
how do you work out contrast threshold if they have given you log contrast sensitivity
do inverse log of CS
do 1 over the answer and times by 100 to get into percentage
Under scotopic conditions the CFF is expected to be what
20Hz
