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PSYC 2390
Lana Trick

thMarch 51 Depth perception Visual angle tells you how far away things are in depth things that are close have large visual angles and small things have small visual anglesBinocular depth cues are cues that allow us to make judgments within a 30 metre range going downstairs threading a needle parking walking down a hallyou are 30 faster and more accurate if you use binocular depth cuesBinocular depth cues involve two eyes and the comparison of the image in between the two eyesWe have a slightly different viewing angle with each eye things appear to move when you look at them with each eyeBinocular disparitydifference what you use inorder to figure out how things areThe degree of difference binocular disparity will tell you how far away something isBinocular disparity retinal disparity mean the same thingJulesz random dot stereogramHow is depth information derived Determine which part on the left eye image matches which part on the right solving the stereo correspondence problemRetinal disparity finding out how far apart the object position is on the left eye as compared to the rightItems on the horopoter the fixation plane the distance away that you are fixating the reference point in the middle of the eye is on the exact same point on the left and right eye if its on the horopterthere is zero disparityItems in front of the horopter the reference point would be on the left side of the left eye and the right side of the right eye crossed disparities the position falls on the opposite sides of the reference pointObjects behind the horopter reference point is on same position on the left and right eye the light rays dont fall on exactly the same point on the retina but they are at least on the right side of the eye uncrossed disparitiesPanums fusion area you can fuse the same image together to get one that looks 3D if something is too much closer than the horopter or too much farther than the horopter you will get a double image but there is an area of space around the horopterThe fact that the tilt after effect transfers from one eye to another it must mean that there are binocular cells that take information from both eyes and transfer to the brain and that they respond to line orientationsStriate cortex and hypercolumns little chunks of tissue that are looking for activity in a particular part of the visual spaceHypercolumns have orientation and ocular dominance columnsCritical period for kittens 4 weeks to 4 months looking for particular experiences to facilitate the development Scientists alternated between placing an eye patch on the left and right eye every day during the critical period cat doesnt have normal depth perception because they caused a disruption in the binocular cells Strabismus is an imbalance in the eye muscles being born cross eyed or walleyed the left and right eye are getting such different information that the brain cannot coordinate them and therefore one eye usually ends up getting suppressed to fix this is should happen before age 4 or 5 because any later will disrupt their depth perceptionChesire cat illusion take a person put them beside a blank wall and balance a mirror in such a way that the blank walls image is being projected on the mirror The person has an image of a friend in their left eye and the wall image in their right and the person will suppress the uninteresting image If you wave your fingers in front of your right eye it will make it appear like they are going through the image of your friendBinocular rivalry one of the images is suppressed and one might be superimposedAmblyopia bad vision might have it in one eyeDifferent actual sizes can produce the same size retinal image the same actual size can produce different retinal sizes different visual anglethThursday March 7 2013we interpret the visual angle of the object and use depth cues to determine size constancy Shape Constancy different shapes can produce the same retinal projection the same shape can produce different shaped retinal projections see the circle when left and right side are the equal distance from you when you rotate it it becomes oblong rotating it in depth one side becoming farther away and one becoming closer but you still see the circleshape constancy is achieved because we take into account depth information ex that the left side is closer than the righteven though the box is a 2D image you cant help but think of it as a 3D box thus you think the dime will fit in itdont touch the page if you manipulate it with your hands the illusion will go awaydouble dissociation were thinking it was a 3D box and your visual system was thinking of it this way similar to the Ponzo illusion applying shape constancy that works in the general worldObject Perception ability to see an object as a whole can take place really quicklyex cow picture very vague need to distinguish the parts from one another figure out what goes together and put it together organizing the information in the imageyou have a pointillistic representation on the retina which means each rod and cone only knows a tiny area on the imagehow does one rod know its on the same object as another rod they donteach only know the tiny area the light shines on drawing all this info together to define a whole object thus is an achievement you may have images that have competing organizationsex Indian rug complicated geometricallyobject recognition is the basis of intelligent behaviourrecognitionrecord the image of object and store it in long term memoryex boy and dog that bit him then you can take a new image say this is what Ive experienced beforestore in the longterm memory the representation of an image ex Biederman machineyou dont need a name associated with something to have object recognition occur you really just need a feeling of familiaritysomething equally as important is object recognitions role in visualmotor coordinationinvolves coordinating your limbs touching avoiding walking etcin order to coordinate your body appropriately you need to represent theobject as a whole you can do that when you have no name and even before you have a memory representation2 approaches to explaining object perceptiontop down approach means you are using your past experience and knowledge andbeliefs to interpret what is in the imagestresses the fact that when you have previous knowledge it can really help you perceive objects when you know what to expect it is easier to see it Richard Gregorydepth perception in the form of reasoning problem solvingalmost as if youre hypothesis testingex A B C D E F then 10 11 12 13 14in the image the B and the 13 are the same but your knowledge and beliefs influence your perception thus you read it correctly in the sequenceperceptual setprepared to see something based on what youexperienced beforeex sax player vs womans face disadvantages of top down theories Missed thisbottom up information from the senses information comes off the eyesretina
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