Light perception Flashcards
What experimental factors important in light perception?
- -Stimulus location
- -State of subjects eye- dark adaptation
- -Wavelength of the test flash-spectral sensitivity curve v lamder
- -Size of stimulus- spatial summation
- -Duration of the test flash-temporal summation
- -pupil diameter
Where is the peak density of cones?
centre of fovea
What cones are found at the centre of fovea?
L and M cones
What field does the centre of fovea have?
small field tritanopia
What do you not find in the centre of the fovea?
Rods
Where is the peak density of rods?
Eccentricity of 20 degrees from fovea
What two types of cells do you find ?
Transient and sustained cells
What are sustained cells?
Cells that give sustained response with light falling on them
What cells give sustained response ?
Midget cells
What do transient cells do?
Cells that only respond to when there is a change in light
What happens in dark adaptation?
Very bright light rhodopsin and cone pigments get bleached after 5 mins rods start to recover but cones are morse sensitive so more dominate
What photoreceptors recovery is faster?
Faster recovery for cones
How long does it take to reach maximum sensitivity?
30- 40 mins
What are the 4 points in dark adaptation? point 1
Rods and cones start dark adapting at the same time
What are the 4 points in dark adaptation? point 2
the more sensitive systems determines the threshold at any one time
What are the 4 points in dark adaptation? point 3
Cones adapt faster than rods 8-10 mins versus 30 mins for rods
What are the 4 points in dark adaptation? point 4
The lowest threshold obtained with rods is much less than that with cones because they are more sensitive
What does the normal retina look like?
Orangish
Why does the retina look orangish?
Photopigments absorb blue-green and bit of yellow light leaving back red-yellow light to be reflected
What happens to a bleached retina?
Photopigments are saturated and cant absorb any more light. All light reflects back and appears white
What is photopigment concentration?
How photopigment density can contribute to adaptation
What is the recovery time for rhodopsin?
Rhodopsin recovery time matches the dark adaptation curve
do retinal cells or photopigments cells respond faster to changes?
Retinal cells faster than photopigments
What wavelength does human eye respond to?
380-780nm
