Exam 2 Material: Vision Flashcards
light
band of electromagnetic radiation (photons)
wavelength determines
color
intensity determines
brightness
what does an object’s color depend on?
wavelength reflected and perceived
- rest of the colors absorbed
transduction
process of turning light into neural signals
how do you get color out of photons?
photons lead to different frequencies which leads to different wavelengths which leads to different colors
what range do we see color in nm
400-700nm
cornea
bends light entering the eye
lens
changes shape to focus light on the retina
Ciliary muscles
adjust focus by changing the shape of the lens
what do the cornea and lens work together to do?
focus light to the back of the retina
help get a clearer picture
Iris
colored ring that expands and contracts the pupil
pupil
allows light to enter the eye
Retina
layer of neurons in back of the eye
fovea
center of the retina
high density of S cones that produce very clear pictures
pupil and iris work together to…
control the size of pupil and regulate how much light comes in
how does the retina receive an image
upside down , but the brain is able to turn the image the right way
accommodation with ciliary muscles
contraction allows for far away objects o come into focus
where does visual processing first occur
retina
Retinal cell types (5)
photoreceptors, bipolar cells, ganglion cells, horizontal cells, amacrine cells
retinal cells that are interneurons
horizontal and amacrine cells
photoreceptors
rods and cones
sensory neurons that detect light
rods
scotopic
low acuity
black and white (no color)
scotopic
dim lighting conditions
cones
photopic
high acuity
color vision (3 types of cones)
photopic
normal, bright light conditions
3 types of cones
S, M, L
S cones
blue
M cones
green
L cones
red
visual acuity
measure of detail, sharpest in fovea
Are there more cones or rods in the retina?
rods
Where are there more cones than rods in the retina?
fovea there are many cones but NO rods
optic disc
no rods or cones, all axons leave the eye to reach brain via the optic disc
the optic disc causes a break in visual field known as a …
blind spot
Blind spot demo with black dot
What happened to the black dot when you read the letters?
it disappeared because the optic disc has no photoreceptors, it cannot see part of the visual field
so there is not a hole in you vision the brain can overcome this
How does the brain accommodate blind spots?
it looks at what is around the blind spot and tries to extrapolate to fill the visual info in for you
visual information received by
photoreceptors
Bipolar cell dendrites receive input from where and synapse where
receive from photoreceptors, synapse on ganglion cells
Ganglion cell axons form the _____
optic nerve
optic nerve
carries information to the brain
what neurotransmitter helps transmit info from photoreceptors to bipolar cells
glutamate
Horizontal cells
in retina, contact photoreceptors and bipolar cells
Amacrine cells
contact bipolar and ganglion cells
horizontal and amacrine cells together…
integrate signals important for filtering info sent to the bipolar cells
- can change activity of rods/cones and the message sent to the ganglion cells
All cell types, except ganglion cells generate ONLY
graded local potentials effecting each other through graded release of neurotransmitter
(little bit of light will cause a little bit of glutamate release)
Ganglion cells conduct
action potentials
each photoreceptor is connected to 1 or more retinal ganglion cells, which convey the signal into the optic nerve towards the
brain
most ganglion cells receive input from ______
multiple photoreceptors
convergence
integration of information
high convergence =
low acuity
if a low convergence that means only 1 message is being dealt with and it will be a
high acuity
the whole area that is visible without movement
visual field
what does the retina represent about the visual field
a 2 dimensional map
organization is preserved as the information travels through the brain as a
topographic projection
much of the topographic projection corresponds to the _____ making high visual acuity possible
fovea
the area in the visual field that a specific cell responds to
receptive field
ex of receptive field
cones respond to specific colors within the visual field
each bipolar neuron only relays information from ______
a small part of the visual field
turning on light in the center of its receptive field excites the cell
on-center bipolar cells
turning off light in the center of the field excites the cells
off-center bipolar cells
the center and its surround are always
antagonistic, opposite
on-center/off-surround
off-center/on-surround
bipolar cells release _______ which always ______ ganglion cells
glutamate
depolarizes
on-center bipolar cells excite _______
off-center bipolar cells excite________
on-center ganglion cells
off-center ganglion cells
bipolar cells release more/less glutamate depending on….
light intensity
changes rate of action potentials in ganglion cells
capacity of an excited sensory cell to REDUCE activity of its neighbors
lateral inhibition
what does lateral inhibition produce?
a contrast effect at the edges of a region
Bipolar cells that relay info from photoreceptors to ganglion cells can also inhibit eachother
some ganglion cells report receiving
less light than they do
can change the message from bipolar cells to ganglion cells
lateral inhibition increases
contrast and sharpness in visual response
what inhibits ganglion cells stimulated by the right-hand edge of each dark panel
cells responding to the lighter band next door
cell getting less light info to sharpen the edges
looks darker because you are shutting down signals of neighboring cells
Herman Grid Illusion
grey dot appears at intersection points of all white lines
- effect is greater from your peripheral vision
- if you focus on a grey dot it disappears
- the intersection falls in the fovea with very little lateral inhibition due to a small receptive field
2 retinal diseases
macular degeneration and retinitis pigmentosa
macular degeneration
leading cause of vision loss
affects central vision
peripheral vision fine
blurs our perception of whatever it is we are trying to look at
retinitis pigmentosa
affects peripheral vision
tunnel vision, cannot see what surrounds your focus
rare genetic disorder
does not usually lead to complete blindness
