Lecture 2 notes
Lecture 2 notes Psyc4106W
Popular in Sensation and Perception
Popular in Psychlogy
This 6 page Class Notes was uploaded by Jennifer Gittleman on Wednesday October 28, 2015. The Class Notes belongs to Psyc4106W at George Washington University taught by Dr. Philbeck in Fall 2015. Since its upload, it has received 16 views. For similar materials see Sensation and Perception in Psychlogy at George Washington University.
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Date Created: 10/28/15
The eye 0 O O Cornea Clear transparent tissue Lens does a lot of focusing of the light Stronger lens than crystalline lens Without it things will look blurry Crystalline lens Another lens in our eye Sclera White part of your eye Choroid Aqueous humour Liquid uid lris Colored part of our eye Muscle that can expand and contract to make a smaller or larger pupil Pupil gets smaller in light and larger in dark ReUna Where rods and cones are take the light energy and change it into electrical energy Rods and cones are connected to ganglion cells carry electrical signals out of the eyeball Optic nerve Collection of the ganglion cell pieces that are exited the eyebaH Where blind spot is no rods and cones can t see anything there Vitreous humour Denser uid Helps keep eyeball spherical Ciliary muscle Control shape of crystalline lens Ligaments Lens power affects image location 0 O O O Sharper image when you have a fat lens and focuses light down more Change the optical power of lens if its at light rays don t get bent as much and the image is farther away Fat lens it moves the point where light rays come together closer If you can t change shape of lens you only see things at one focus Object distance affects image location 0 On top object is far away o On bottom object is close Accommodation 0 Changes shape of crystalline lens to make objects at different distances come into focus 0 Start to increase shape of crystalline lens make it fatter point of convergence goes on retina so you have a clear image 0 If you move object closer to eye you can still create a sharp image but you have to make crystalline lens even fatter 0 Near point closest thing you can look at without losing focus 0 Changing crystalline lens let s us focus things up close and far back Hyperopia farsightedness 0 You can see far things clearly 0 You have trouble seeing near things clearly it looks fuzzy o No matter how much you try to change fat in your lens it won t bring point of convergence up to your retina if something is close up you need to make your lens fat 0 Corrective lens help focus light more Myopia nearsightedness 0 You can see near things clearly 0 You have trouble seeing far things clearly it looks fuzzy o Converging inside your eyeball Stigmatism 0 Where your eye doesn t have the same amount of optical power in all directions Presbyopia 0 quotold eye or old visionquot 0 Eye gets more rigid and harder to change shape of lens 0 Lens gets stuck in one shape Measurement of Image Quality 0 Snellen Chart 0 Landolt Rings If you have trouble seeing they would not be able to see the gap 0 2040 you can see something clearly at 20 feet that a normal person can see at 40 feet away 0 2020 you can see something clearly at 20 feet that a normal person can see at 20 feet away ReUna o Rods and cones Cells that take light energy and change it into electrical signals that the brain can use Where the transduction process happens is in the outer segments Rods have a squared off shape at top and cones come to a point at the top Connect to horizontal cell tend to connect rods and cones to each other Bipolar cells connect horizontal and amacrine Amacrine cells connections between bipolar and ganglion Outer segments have platelike structures in plates are photopigment molecules change their physical con guration when light strikes them changes chemical properties of cell and changes electrical properties of cell 0 Thresholds vs Sensitivity o lnversely related if you re highly sensitive you have a low threshold and vice versa Ex if you are not sensitive to pain you have a high threshold for pain 0 Absolute Thresholds 0 What s the smallest amount of light that let s you see 0 Hecht Schlaer Pirenne Sit in the dark for at least 30 mins Not look directly at the light Fovea densely packed with cones Give them a xation point and then put a spot of light off to the side 20 degrees where we have the most rods Bluishgreen light maximizes sensitivity to rods Reddish light minimizes sensitivity to rods Photon little packet of light energy smallest amount of light energy that you can have Shows you all the things you have to do to get to max sensitivity and when only 7 are excited we have a perceptual experience 0 Duplicity Theory von Kries o Rods Things tend to look blurry because of lower acuity and convergence Lots of sensitive cells feeding into one ganglion cell it s more sensitive o Cones Requires more light for them to respond More of a onetoone relationship 0 Dark Adaptation Experiment 0 Just turned off lights and looking at a screen 0 Given method of adjustment can control spot in front of you with a knob until you can barely detect it o Sitting in the dark for a while doing this OO 0 First part of curve is cone vision and second part is rod vision Threshold experiment Around about 710 minutes you don t make any more adjustments cone vision but after 10 minutes you can see it again and keep turning it down rod vision You can test cone vision if you have a light that only hits the fovea only uses cones You can test rod vision by getting someone who only has rods due to a genetic mutation We have two different types of photoreceptors one that s specialized in higher light levels and lower light levels and they dark adapt at different rates Photo pigment molecules do not regenerate all at once once they get hit by light they are not able to catch more light so when you spend more time in the dark they become sensitive again and are able to catch light the more time you spend in the dark the readier they are to catch light be able to draw curve and have that notch in it label both axis specify if we re talking about threshold or sensitivity if it is sensitivity you have to ip the hi and low low at top and high at bottom of axis what is it that causes the dark adaptation regeneration of photo pigments we have rods and cones that adapt at different rates and at what times are they most sensitive is Light Light has a wavelength Visible light a part of a larger spectrum of electromagnetic radiation what our eyes are sensitive to and can see 400700 nanometers Newton s Prism Experiment Cut a hole so that the red part would pass through one hole and for each color on the other side you had the lights come out on the other side the prism isn t generating the colors all the colors are part of the original white light coming in When you recombine the colors you get the white light again white light is made up of different kinds of light which vary in wavelength Intensity the intensity of light is how hard it s raining you want to know how long you re collecting if you re measuring for a couple of seconds or an hour you re going to catch more rain if you use a big pot Monochromatic light only has one wavelength Microspectrophotometry pass light through tube and have a detector so you know what intensity of light you re shooting into it and measure how much comes out on the other side if the photoreceptor isn t sensitive to the light so most will come out on the other side 0 Short wavelength sensitive to 419 nm 0 Medium wavelength sensitive to 531 nm 0 Long wavelength sensitive to 558 nm Dendrites where cell gets signals from other cells inputs come in from here Nucleus metabolic needs take place Cell body contains nucleus averages all the inputs that are coming in through dendrites Axon long process signals get carried over long distances Terminal branches make contact with dendrites with a different cell Synapse where the cells communicate with each other when the signals are going to terminal branches you have little pockets of chemicals called neurotransmitters and when you get a lot of action potentials it makes the pockets migrate to the boundary of the terminal branch and they ll open and release chemicals between gap between the two cells the dendrites on the neighboring cell are looking for the neurotransmitter molecules when the molecules match up it causes an electrical change in the dendrite it s an electrical and chemical process between neurons it s a chemical process Action potential changes the electrical charge of the cell early on resting level of electrical charge then spikes up very quickly then comes down and rebound always looks the same doesn t get bigger you just have more of them we can measure action potentials Lateral inhibition a lot of our visual processing is done by a way of having interactions between neighboring neurons direct demonstration of communication between neurons 0 Limulus horseshoe crab has large visual neurons light coming in on A and have an electrode poked into it which determines if cell is producing action potential 0 If you shine a light on B you see a decrease in A o The more light you shine on B the less ring rate of A 0 Showing that somehow A and B are connected and sending signals to each other Misapplied size constancy allusion our ability to take account into changes of distance Ganglion carry visual signals out of eyeball through the blind spot bundle of ganglions are optic nerve Rods and cones difference how they connect to ganglion cells rods are more sensitive to light than cones rods are lower in acuity than cones 0 Diagram left is rods right is cones many rods feed into one ganglion one cone feeds into one ganglion for cones it has higher resolution because of onetoone relationship rods and cones are converging onto ganglion cells higher level of convergence for rods rods are more sensitive because ganglion cell is catching light from all different rods lower left each individual ganglion cell isn t as sensitive for cones lower right Receptive elds 0 0 Single unitcell recording cat diagram You poke electrode in cell visual neuron Put spots of light onto screen in front of animal Number of action potentials would increase in certain regions Number of action potentials would decrease in certain regions Receptive eld on center off surround bulls eye in middle 0 Put light where are Receptive eld off center on surround bulls eye in middle 0 Put light where the are Area of retina that when stimulated put light on it in uences ring rate of cell Mach band illusion of it being darker on one side emphasizes the edge 0 Lateral inhibition diagram 0 O O O Dots show that they are inhibiting each other d is getting inhibited my something else B would be active at 100 but 10 is taken away Can explain mach band and simultaneous contrast The more neuron is ring because more light is hitting it it takes away some ring from its neighbors if cell is more active turns down neighbors more Simultaneous contrast 0 O Decrease in ring rate of cells from left increase in ring rate of cells from right Getting more inhibition from its neighbors because there is more light around it left Getting less inhibition from its neighbors because there is less light around it right
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