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What is light?
Light is a form of electromagnetic radiation, it differs from other electromagnetic radiation in wavelength
How long is the wavelength for light?
Between 400 and 700 nanometers
What are the wavelengths for the colors:
Red, yellow, green, blue, and violet?
- Violet: 400
- Blue: 500
- Green/yellow: 600
- Red: 700
What is the Wavelength order for colors?
Violet (short)--------->red (long)
3 types of interaction light has with matter
- 1. Absorption
- 2. Refraction (photon's course is bent)
- 3. Reflected (a certain % of photons is reflected depending on thickness of object)
Does color exist in light?
No, wavelengths give off color but there is not color in light
Why is color a psychological variable?
It is created in our brain
What gets refracted more, short or long wavelengths?
Shorter wavelengths get refracted the most leading to long wavelengths
How does a lens form an image?
They bring parallel light waves into focus
The greater the curvature of the lens, the more refraction on the light
What is floater?
Floaters are dead cells floating in the vitreous
What does the cornea do and where is it located?
The cornea refracts light and it is located in front of the pupil/iris
What is the fovea?
A small area in the retina of the eyes where acuity is the highest.
What does the iris do for the pupil?
The iris can change diameter to make the pupil bigger or smaller; this allows for different amounts of light to enter the eye
What does the nervous system do to pupil size?
The parasympatetic reduces pupil size and the sympatetic increases pupil size
Autonomic N.S. is involed with arousal
Where is the retina located and what does it do?
The retina is located all around the back of the eye and it turns light it to neurological information that is sent to the brajn
What happens when the lens in our eyes is flat?
Our vision is focused on objects that are far away
What happens when the lens inside our eyes is round?
There is more curvature and our vision is focused on objects near by
What is myopia?
Myopia is when we are nearsighted; we need a negative lens to spread out light before it hits our internal lens
What is hyperopia?
Hyperopia is when we are farsighted and need a positive lens to focus light a little more before our internal lens
What is astigmatism?
When your eyes have a different radius of curvature so they cant focus a point
What is presbyopia?
Presbyopia is due to aging; it is when the pupils shrink and our ability to accomodate reduces, making is hard to focus on near things
What are the types of cells that the retina is made up of?
In order from the vitreous to the back of the eye:
- Ganglian cells
- Amacrine cells
- Bipolar cells
- Horizontal cells
- Rods & Cones
What do ganglion cells do?
They send informarion to the optic nerve
What do bipolar cells do?
They connect ganglian cells to the rods and cones
What are rods and cones?
They are the photoreceptors in the back of the retina that absorb light
Where are photo-pigment discs located and what do they do?
Discs od photo-pigment are fond in cones and rods.
They absorb photons of light and which break up pigment molecules, becoming hyper polorized
What happens after a photo-pigment is broken down?
After a photo-pigment is broken down, transduction occurs which is changing a physical stimulus into a neuro representation of that stimulus
What is transduction?
The conversion of physical energy into neural activity
What is bleaching?
Bleaching is when a photon has been absorbed by a molecule of photopigment.
The molecule is broken down and the photo receptor is less sensative because the pigment cant absorb light any longer
What is light adaptation?
The reduction in photoreceptor sensitivity following light exposure.
The exposure to light redudes light absorbtion and it takes a while for thr photopigments tp reform
What is dark adaptation?
Dark adaptation is when, you return to a dark area and photopigments slowly reform, increasing sensitivity to light.
What are rods sensitive to?
Rods are sensative to low light and black & white colors.
They are found all around the retina except the fovea
What are cones sensitive to?
Cones are sensative to high light and color.
They can be found abundantly in the fovea.
What is our blind spot?
Our blind spot is where the optic nerve is located. But we can't point it out because our brain fills it in slowly according to what is around us
Why don't we see our retinal vasculature?
We dont see our retinal vasculature because although photons are absorbed by blood vessels, enough light reaches sensitive light receptors and because they remain statonary.
Why can we see floaters?
We can see floaters becuase their constant movement does not let our photoreceptors to adapt
What is more sensitive, a cone that has a blood vessel in front of it or a cone that absorbs light directly?
they both have same amount of sensitivity...the cone that absorbs ligth directly is constantly in bleach so its sensitivity goes down and the cone with the vessel in front of it doesnt get as much light because photons get absorbed by the blood.
What is the optic nerve composed of?
What are the two types of optic pathways?
Tectopulvinar and geniculostraite
What areas does the Tectopulvinar pathway involve?
Optic fibers go straight from the eye and cross at the optic chiasm. Then from there they go to the SUPERIOR COLLICULUS and after to the PULVINAR NUCLEUS and ending at the occipital lobe
What areas does the geniculostraite pathway lead to?
Optic fibers head to the LGN lateral geniculate nucleus then the occipital lobe
What are the two types of optic fibers?
The naisal hemiretina and the temperal hemiratina.
What are the fibers that are located on the outer sides of our eyes called?
Fibers that end up on the same side of the brain are ipsy-lateral. Aka temperal hemiretinal
What are the fibers that are located on the inner sides of our eyes called?
Fibers that end up on the opposite side of our brain are contra-lateral. Aka naisal hemiretinal
How is our visual field set up?
Things that land on the right visual field of both eyes end up on the right side of the brain, and vice versa
Where does visual information go to after the occipital lobe?
After the occipital lobe information is sent to the temperal lobe
What is cortical magnification?
Cortical magnification is the fact that more cortex is devoted to processing central as compared to peripherap vision.
From the occipital lobe, what are the two pathways that lead to the cortex?
The dorsal (top back) and ventral (front) pathways
What does the dorsal pathway lead to and how does it relate to vision?
The dorsal pathway leads to the parietal lobe and it is related to the "how" of vision; as in how we interact with what we see
What does the ventral pathway lead to and how does it relate to vision?
The ventral pathway leads to the temporal lobe and it is related to the "what" of vision; as in what objects are qnd how we recognize them
What do ganglion cells tell the brain
The ganglian cells tell the brain that rods and cones are getting light
What is a receptive field?
A receptive field is a region of photoreceptors a ganglion cell gets inhibited or exited by.
When the receptive field has either a positive or negative stimulus, signals are sent to the brain
What happens to a ganglion cell when a receptive field is both inhibited and exited by the same amount of light?
The ganglion cells sends no signal because it stays in its resting phase
Can receptive fields overlap?
Yes, when receptive fields overlap there can be neural convergence and divergence
What is neural convergence?
Neural convergence is when many cones and rods influence one ganglion cells
What is neural divergence?
Neural divergence is when one cone or rod can influence many ganglion cells
What is a simple cell receptive field?
A simple cell receptive field is a visual cell that has only one area that exites the cell and the area around it inhibits the cell.
What is a complex cell receptive field?
A complex cell receptive has an area that is stimulated by light coming at a certain orientation.
What is a hypercomplex receptive field?
A hypercomplex receptive field is an area where the neurons only respond to a certain type of movements
What is a parvocellular system?
A parvocellular system has smaller rdceptive fields and sustains responses to color
What is a magnocellular system?
A magnocellular system has big receptive fields and slow responses to moving objects
What is spacial summation?
Spacial summation is adding the responses from two areas in space
What is lateral inhibition?
Lateral inhibition is when surrounding inhibitory rods & cones cancel an exitatory response
Where do parvo-cells lead to in the brain?
Parvo ganglion cells lead to the parvo lateral geniculous nucleus through 3 visual pathways (3rd one is for color) and into the temporal lobe via ventral pathway
Where do magno cells lead to in the brain?
Magno ganglion cells lead to the magno lateral geniculous nucleus through 3visual pathways and then a movement pathway into the parietal lobe via dorsal pathway
How does brightness contrast affect the center of a region?
Our perception of a center region is affected by the surroundings
For brightness of a region, what is our perception influenced by?
Our perception is influenced by how much light is coming at us from an object
What is lightness constancy?
Lightness constancy states that the lightness of an object is based on the % of light reflected by that object
What is constancy and what types of constancy are there?
Constancy is the tendancy to percieve constant properties of objects.
- There is:
- Light constancy
- Size constancy
- Shape constancy
What do the Mach bands tell us about light and dark objects next to each other?
The mach bands tell us that we percive thongs to be light and darker along the edges of an object based on its surroundings
What is the Hermann Grid and what does it teach us?
The hermann grid is a grid of squares that make us percive shadows at intersections when fixated on a point. It teaches us that the areas that dont have our focus are percive to have a shadown because there is lateral inhibition occuriing on the receptive fields.
The alleys between two squares have an exitatory response in the receptive field so they appear to have light
What are the three types of acuities?
- Snellen acuity
- Vernier acuity
- Stereo qcuity
What is Snellen acuity?
Snellen acuity is the ability to see fine details
What is vernier acuity?
Vernier acuity is being able to detect the offset of two objects
What is stereo acuity?
Stereo acuity is being able to tell the difference in location of an object, in our eyes
What is fourier analysis?
Fourier analysis (decomposition) is taking a square wave/complex wave and breaking it down to multiple simple waves like sine waves
What is the contrast sensitivity function?
The contrast sensitivity function tells us how sensative we are to various frequencies (waves lengths) of visual stimulous
What is spacial frequency?
Spacial frequency Is trying to see how many frequencies can fit into a dregree of vision
How is contrast related to spacial frequency?
To see a certain spacial frequency, you need a level of contrast
For spacial frequency, what do bit and small cells respond to?
Big cell receptors respond to simple parts od an object, small cells respond to details of an object
What does fog do to light?
Fog scaters light
What happens when you look at a certain frequency for too long?
Your contrast sensitivity is reduced
What happens when the frequency your are looking at for a long time turns out to be a square wave?
When you are staring at a square wave frequency for too long, you loss sensitivity for multiple frequencies
What is the trichromacy theory?
The trichromacy theory states that by mixing BLUE RED &GREEN you could create any color; simply tweeking the amounts you mix
What happens when you mix colors containing pigments?
Pigments absorb most light so by mixing pigments you subtract the amount of light you can see
How can we obtain the color white?
Becuase color is a psychological variable, the only way to obtain white is by mixing light
What did George Palmer say about the retina?
That there was three color receptors in the retina
What is the opponent Process theory?
The opponent process theory states that there are four primary colors:
Red, blue, green, and yellow
It also states that each color has an opposite which cant be experienced at the same time:
According to the opponent process theory, what happens when you stare at one color for long enough then looked away?
The neuron sensitive to that color would be beyond its resting phase and would be very sensitive to its color opponent (color opponent afterimage)
What did the spectra of cone absorption show?
It showed that every cone haa one of the 3 peek absorbtion. This proved the trichromacy theory
What does it mean to be a trichromat?
It means that the color matches people can is no like normal people
What does a dichromic people see?
They see no difference between red orange and yellow