How Do We Detect Light? Flashcards
light
electromagnetic radiation
electromagnetic wave that we can detect (aka photons)
what distinguishes the different colors of light
wavelength of light
red light= higher wavelength, lower frequency (moves slower)
purple/indigo light= lower wavelength, higher frequency
frequency
cycles per second (Hertz)
some electromagnetic radiation we cannot detect
UV rays, infrared, etc.
radio waves
higher wavelength, lower frequency
travels through the air, radio takes the wavelengths-> transforms them into things we can hear-> how we have a radio
human vision vs. dog vision
dogs don’t have the ability to see as many colors as we do
we only see colors based on the cones and number of cone receptor cells we have
dogs
2 cone receptor cells
humans
3 receptor cells
human vision vs. snail vision
snails see in black and white, but don’t see in the same acuity as humans
snails see within our visual spectrum, but with less acuity (shockness, clearness)
acuity
clearness
human vision vs. gecko vision
gecko’s can receive and detect spectra that humans cannot see and protect
can see into the UV light spectrum (lower wavelength, higher frequency)
pheromones
all mosquitos detect and if you get eaten, its cause you have sweet pheromones
human vs. snake
snakes can detect heat
see wavelengths (longer) than we can see, on the infrared spectrum
human vision vs. bird vision
can see shorter wavelengths (UV spectrum)
can see more bright things
human vision vs. mantis shrimp vision
12 photoreceptors that detect color vs. 3 photoreceptors in humans (3 colors)
physics of light
white light is made up of the spectrum of all the colors (ROYGBP).. put white light into a prism, (rain causes) light bends at different angles depending on wavelengths-> see a rainbow
see the separation of white light into all of those colors
when we see colors
colors are being absorbed
black= absence of wavelength (0 photons coming into my eyes)
packet of energy
photons, which are both particles and waves
energy from lights come into our eyes
number of photons emitted by source
brightness
bright white light or dim white light (it will be white either way)
frequency of photon waves
color
wavelengths determines the color
light -> vision
white light bounces off the background of the slide… wavelengths bounce off and come into our eyes
black and red
black- no wavelengths bounce off
red- only red wavelengths are being bounced off and entering eye
all other color wavelengths are being absorbed, no red wavelengths to bounce back… apple looks black
shine only green light onto a red apple
green wavelengths get absorbed, no red wavelengths to bounce back… apple looks black
Class Question: The frequency of light waves conveys information about ____, while the frequency of sound waves conveys information about ____
A. Color; loudness
B. Color; pitch
Wavelength or frequency of the light = color
C. Brightness; loudness
Brightness = number of photons
D. Brightness; pitch
B. color;pitch
structural features of the eye
cornea
retina
lens
pupil
iris
cornea refracts and is inverted
light entering the eye so that it is transferred to retina
inverted top-bottom and reversed left-right
lens
focuses image on retina by changing shape
pupil
opening in the iris
pupil controls
how much light enters
brightness
optometrist dilates pupil by blocking acetylcholine transmission in iris muscles
retina has
photoreceptors
visual processing begins in the retina
photoreceptor cells
rods and cones
rods
scotopic
1 photoreceptor, 100 million
more common in peripheral parts of retina
very high sensitivity-> respond in low light conditions, and saturated in bright light
wavelength insensitive (gray)
cones
photopic
3 photoreceptors, 4 million
more common in fovea
low sensitivity-> only active under brighter conditions
wavelength sensitive (colors)
fovea
center of the retina (more cones)
transduction
photoreceptor cells transduce light to electrical signals to chemical signals
transduction steps
light deforms rhodopsin in rods (photopsins for cones)-> releases transducin (like a G-protein)-> transducin activates PDE (phosphodiesterase)-> PDE reduces cGMP levels-> less cGMP causes Na+ channels to close-> hyperpolarization
*1 photon closes hundreds of Na+ channels and blocks 1 million Na+ ions
light _____ the photoreceptor cell->
hyper polarizes-> leading to less glutamate release
cones have the same general mechanisms as
rods
but, photopsins are deformed by specific ranges of wavelengths
three separate opsin proteins
three type of cones
color blindness
usually only can distinguish short wavelength from long wavelength
retinal cells include
photoreceptor cells
bipolar cells
horizontal cells
amacrine cells
photoreceptor cells
release glutamate onto bipolar cells
bipolar cells
synapse onto ganglion cells, whose axons form the optic nerve fibers
lateral interactions
horizontal cells
amacrine cells
horizontal cells
contact photoreceptor and bipolar cells
amacrine cells
contact bipolar and ganglion cells
bipolar cells integrate
a bipolar cell receives info from multiple photoreceptors, so can monitor and integrate what they are all “seeing”
two types of bipolar cells
photoreceptor cells steadily release glutamate onto bipolar cells
light causes less glutamate release
on-center vs off-center
on-center bipolar cells
turning light on in the center of the field (less glutamate) excites them
off-center bipolar cells
turning off light in the center of the field (more glutamate) excites them
bipolar cells release glutamate, which always…
depolarizes ganglion cells
What happens to an off-center bipolar cell when you turn off a light in the center of its field?
A. It is inhibited
B. It is excited
C. Nothing
B. It is excited
ganglion cells integrate
a ganglion cell receives info from multiple photoreceptors (via bipolar cells), so can monitor and integrate what they are all “seeing”
ganglion cells receptive fields
on/off center surround ganglion cell
bipolar cell responses
changes in polarization
ganglion cell responses
action potentials
pathway to the brain
optic fibers pass through the retina
blindspot or optic disc
where ganglion cell axons (optic nerves) cross retina to enter the brain
ganglion cell axons-> optic chiasm
the optic nerves (ganglion cell axons) from each eye join at the optic chiasm
side of chiasm
some axons with stay on same side (ipsilateral) and some cross (contralateral)
visual fields
left and right visual fields
binocular vision
in the center region of visual field
depth perception
requires visual field overlap
in the end
all axons carrying information about the left visual field end up on the right and vice versa
which optic nerve fibers stay on the same side?
the temporal (lateral) retina views a shared part of the visual field, so those fibers stay on the same side
which optic nerve fibers cross?
the nasal (medial) retina views the non-overlapping part visual field, so axons cross over
Which retina (A or B) will detect the
orange circle?
Which side of the brain will information
about this orange circle be received?
A B
both retinas- orange circle is close to the middle
B- left visual field is transferred to the right
optic fibers -> lateral geniculate nucleus
optic fibers (ganglion cell axons) pass through optic chiasm and synapse in lateral geniculate nucleus (LGN: part of thalamus)
lateral geniculate nucleus layers
the LGN has six layers
each layer receives input from only one eye
magnocellular & parvocellular
magnocellular layers
(1 and 2) receive information from rod cells
depth and motion
large receptive fields
1 from one eye, 2 from the other eye
parvocellular layers
(3 to 6) receive information from cone cells
fine detail and color
small receptive fields
3 and 5- one eye, 4 and 6- other eye
LGN-> primary visual cortex (V1)
LGN axons send information to the primary visual cortex (V1)
retinotopic (location) map in V1- topographic organization
V1 is retinotopically organized-> neighboring cells tend to receive information from multiple nearby ganglion cells
V1 cells receptive fields are bigger than LGN fields
V1 “simple neuron” receptive fields
each “simple cell” monitors a small stripe of the visual field
responds to bars and edges present in that location
orientation matters- horizontal, vertical, slanted
V1 “complex neuron” receptive fields
each “complex cell” monitors a larger stripe of the visual field
responds to movement
orientation matters
complex V1 neurons receive from
simple V1 cells<- LGN cells<- V1
retinotopic maps in V1 allows for
detection of bars/edges and movement in spatial representation
a second level of topographic organization
ocular dominance column/slab
ocular dominance column/slab
vertical column of neurons in V1 that respond to one eye
adjacent column of neurons respond to other eye
same receptive field
third level of organization
orientation column
orientation column
vertical column of neurons that respond to rod-shaped stimuli of a particular orientation
two pathways of higher order visual processing
dorsal (where) pathway & ventral (what) pathway
starts at the occipital lobe
ventral “what” pathway
V1-> V2
V2-> V4
V4-> IT
V1->V2
V2 combines information from multiple V1 neurons to build complex representations
textures
multiple actual features and some illusionary features
filling in gaps of shapes
V2-> V4
V4 neurons respond to complex radial and concentric stimuli
wavelength (color) specific receptive fields
V4-> IT
inferior temporal cortex responds to complex shapes, sensitivity to color and texture
facial recognition (fusiform face area)
prospagnosia or “face-blindness”
IT
inferior temporal cortex
What will a patient with damage to V4 be likely unable to perceive?
A. the brightness of the lights on the roller coaster
B. the color of the roller coaster
C. the motion of the roller coaster
B. the color of the roller coaster
dorsal “where” pathway
V1-> V5
V5-> posterior parietal cortex
V1-> V5
V5 neurons perceive speed and direction of moving stimulus
motion blindness
V5
medial temporal lobe
V5-> posterior parietal cortex
neurons tuned to spatial location of objects
planned movements, visuomotor transformation
lesions in the posterior parietal cortex
hemi-spatial neglect
visual->motor is biasing one side over the other (able to engage both sides when prompted)
What will a patient with damage to the medial temporal area (area
V5) be likely unable to perceive ?
A. the brightness of the lights on the roller coaster
B. the motion of the roller coaster
C. the color of the roller coaster
B. motion of the roller coaster
