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Psych 2115 oct 7.docx

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Western University
Psychology 2115A/B

Psych 2115 October 7 Diagram of the eye from textbook, side view of eye looking up Stuff at the back of the eye In the retina you find the sense organs- the rods and cones. They absorb the light and give work to the phenomenon of vision. In the center of the retina is the fovea- the most sensitive part (looking at things in great detail). The rods and cones collect the light and the start the process of sending info to the brain- the info has to leave the rods and cones and go to the brain through the optic nerve- the rods and cones are connected to bipolar cells, bipolar cells are connected to ganglion cells, these all come together to form the optic nerve. A weird thing is that the bipolar and ganglion cells are in front of the rods and cones, away from the optic nerve, so how do you turn the info around and get it to the optic nerve? When the info hits the rods and cones they send the info to the bipolar and ganglion cells, the bipolar and ganglion cells then converge together and leave the eye through the optic nerve. The blind spot- a little point on your eye where you will not get any sensation of vision because there are no rods and cones there to observe light. When the information is being sent to the brain, and the ganglion and bipolar cells are leaving through the optic nerve, there are no rods and cones at that one spot where they're leaving through (the blind spot)- it's not in the center, they're rotated in a bit at about 16 degrees inward (where the optic nerve is). Cones: about 5 to 6 million cones in an eye. Largest concentration is in the middle (in the fovea), if you want your cones to be working that’s where you want to stimulate. They're very sensitive and the send colour information to the brain. They're sensitive because many of them are connected to a single bipolar cell and then a single ganglion cell- have their own pathway to the brain. This is not always the case but by and large a given bipolar cells will not have many cones feeding into it, and a given ganglion cell will not have many bipolar cells leading to it. Cones are basically all at 0 degrees (middle of the fovea) Rods: Rods tend to be where the cones are not. Rods are clustered at about 20 degrees on either side of the retina (20 degrees to the left and to the right), very few rods in the fovea (in the blind spot - 16 degrees out, no receptors at all). About 120 million rods. Rods do not have individual pathways to the brain, any given rods response wil be feeding into the same bipolar cell and a number of rods in its vicinity, the information that the bipolar cells get will be sort of a "summary" of all the rods that are connected to it- you wont get fine grain info. Rods cannot get you fine grain info but they're very sensitive- you don’t need much light hitting an area to get a response. For one bipolar cell, if just 100 of them have enough activity to be stimulated they can stimulate the ganglion cell to respond to the light (the most sensitive place for this is 20 degrees off the fovea because that’s where most of them are). A bipolar cell can only have rods or cones connected to it, not both. Dark adaptation: adapting to the darkness in a room- one way to measure this is to check what your threshold is. When you first enter you're going to have a threshold for a stimulus which is very high (need a lot of stimulus to see), over time it will go down (1) Found an odd shaped curve. What's happening here is that we're seeing the differential effects of rods and cones. Figured this out by stimulating areas that only have rods or only have cones (ie. fovea and 20 degrees away from fovea). Rods and cones have different dark adaptation. They are maximally sensitive to different wavelengths. There are 3 types of cones and each of those are maximally sensitive to different wavelengths; but all in all there are different wavelengths that rods and cones are maximally sensitive too. Rods: 505nm Cones: 550nm (longer) Purkinje observed that there was a real changing pattern of brightnesses in coloured areas over the course of the day. In the day time the reds seemed very vibrant and the blues seemed less vibrant, the reason this is happening was because in the day light that’s when the cones do most of there work and the cones like those longer wavelengths so the respond better to those colours, but as night comes the rods start to take over and now those reds (which rods don’t like cause they have long wavelengths) now don’t generate much of a response. The blues and greens seem brighter. This is known as Purkinje's shift. Rods don't like red at
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