perception 2 Flashcards
what is visible light?
band of energy in electromagnetic spectrum
what are the different wavelengths of light?
400-700nm
what are the different wavelengths of light associated with?
different colour perceptions
what does light consist of?
photons
what is luminance?
number of photons in space, associated with brightness perception
what is absorption?
photons collide with particles of matter
what is reflection?
light strikes opaque surfaces
what is transmission?
light passes through transparent matter
what does the eye use to project an image onto the retina?
convex cornea and lens
what do photoreceptors do?
transform light into an electrical potential
how do light signals leave the eye?
flow through neurons to retinal ganglion cells
then out of eye via optic nerve
where are rods located?
in the peripheral retina
where are cones located?
centre of retina (fovea)
which can operate in low light- rods or cones?
rods
why are rods sensitive to light?
many rods join to one neurone, so many weak generator potentials combine to reach the threshold
why are cones less sensitive to light?
one cone joins to one neurone, so it takes more light to reach the threshold and trigger an action potential
why do rods have low visual acuity?
many rods join to the same neurone, so lights from two points close together can’t be told apart
why do cones have high visual acuity?
one cone joins one neurone, so the brain receives separate action potentials for each form of light
how many photopigments do cones have?
3
what are the different photopigments in cones sensitive to?
short
medium
long
wavelengths of light
what is the visual pathway from the retina to the brain?
retina
optic nerve
optic chiasm (optic nerves cross)
LGN
primary visual cortex (receives and integrates visual info)
what is bottom up brightness perception?
responses to brightness are caused by processes within the retina
what is top down brightness perception?
brain uses knowledge about how light interacts with objects to determine perceived brightness
what is light/dark adaptation?
sensitivity of retina constantly adjusts to compensate for changes in luminance
increases when low, decreases when high
what does light/dark adaptation mean the retina encodes?
contrast=
ratio of object’s luminance relative to the background luminance
what is lateral inhibition?
information processing in retina
retinal ganglion cells receive excitatory and inhibitory input from neighbouring photoreceptors
what is the influence of lateral inhibition?
makes visual system sensitive to changes in luminance
this helps detect the edges of objects
affects perceived brightness
what photopigment do rods contain?
rhodopsin
which photopigments can cones contain?
S cones
M cones
L cones
what are S cones?
blue cones, sensitive to short wavelengths
what are M cones?
green cones, sensitive to middle wavelengths
what are L cones?
red cones, sensitive to long wavelengths
what are the three photopigments in cones known as?
trichromacy
what is monochromacy?
individuals have 0/1 functioning cone types
what is dichromacy?
individuals have 2 functioning cone types
what is anomalous trichromacy?
individuals have a defect in one of three cone types
what is colour opponency?
retinal ganglion cells receive excitatory or inhibitory input from different cone types
=red/green and blue/yellow pathways
demonstrated using negative afterimages
what is colour perception?
top down
tendency for the perceived colour of objects to remain the same, even if the lighting changes
