VF - Temporal Vision 1 - Week 4

Question 1

Which cells detect flicker, and are they sensitive to colour?

Answer 1

Magnocellular cells, and are colour blind.

Question 2

Define Blochs law.

Answer 2

Within the critical duration, a given amount of luminous energy has the same effect on detection threshold regardless of its distribution in time (Luminance x duration).

Above the critical duration, there is no temporal summation, so threshold simply depends upon luminance, independent of duration.

Question 3

Define Critical Flicker Frequency.

Answer 3

Transition point between a steady light and flickering light.
usually taken as the frequency where there is a 50% probability of the light being seen as flickering.

Question 4

Name 7 factors affecting the critical duration.

Answer 4

Light level
Size of the stimulus
Type of task
Wavelength
Intensity
Spectral composition
Area of the stimulus

Question 5

Define Ferry Porter law

Answer 5

CFF increases with luminance, in direct

proportion to the logarithm of the luminance

Question 6

Describe the neural basis for the Ferry Porter law.

Answer 6

The level of activity of the inhibitory neuron is dependent upon the excitation it receives. The inhibition can be feed-forward inhibition or lateral inhibition.

Question 7

How does wavelength affect the critical duration?

Answer 7

Increases the critical duration.

Question 8

How do light levels affect critical duration?

Answer 8

Darker backgrounds increases the critical duration.

Question 9

How does the size of the stimulus affect critical duration?

Answer 9

Smaller stimuli increases the critical duration.

Question 10

How does the stimulus intensity affect the critical flicker frequency?

Answer 10

Increases with stimulus intensity.

Question 11

What is the Granit-Harper law?

Answer 11

Ferry-Porter relation increases with no change in slope as you increase stimulus size.