thresholds for seeing

Question 1

In order to measure absolute threshold you must optimise:

Answer 1

the state of dark adaptation
position of the light on the retina
the wavelength of the test light 
the size of the test flash
the duration of the test flash

Question 2

explain the order of dark adaptation in photo-pigments in the retina

Answer 2

Cones adapt faster enabling us to initially see in a dark environment
Adaption of rods then decreases the threshold for seeing even further.

Question 3

comment about the composition of photosensitive cells in the forvea

Answer 3

Fovea is absent of cones hence we are blind in our fovea in darkness
also absent blue cones

Question 4

explain the breakdown of light absorption starting from the cornea

Answer 4

90 photon quanta reach the cornea 
3% reflected
Estimated 50% absorbed by optic media
43% reach back of eye
Estimated 20% adsorbed
Therefore at 20 degrees of freedom the probability of more than 1 photon detecting is very low Rods can respond to 1 photon

Question 5

Hect et al’s study on thresholds for seeing follows the psychometric function but what is the psychometric function

Answer 5

A psychometric function is an inferential psychometric model applied in detection and discrimination tasks. It models the relationship between a given feature of a physical stimulus, e.g. velocity, duration, brightness, weight etc., and forced-choice responses of a human or animal test subject.

Question 6

evaluate Hects study

Answer 6

response bias from researcher–observers tendency to say yes or no is going to influence the participants estimation of either they had seen the stimulus.
participant bias depending on weather they have a conservative attitude or not
60% arbitrarily chosen