1 Sensation and Perception Exam 6 Study Guide Vision IV Perceiving and Recognizing Objects Part 1 Middle Vision What is middle vision Middle vision visual cortex and is getting us to object recognition loosely defined state of visual processing Happens after primary After basic features have been extracted from the image early vision up to and including striate cortex Before object recognition and scene understanding high level vision Goal to organize elements of a visual scene into groups that we can then recognize as objects Middle vision is like a collection of specialists each with an area of expertise and individual opinions about what the input might mean The goal is to have a single answer emerge out of lots of opinions Middle vision gets us from broken down image to recognizable image Organizes different parts of the visual scene into groups so we can recognize the house flagpole tree on ppt etc Happens in 18 19 broadmans area circled in picture Examples Filling in edges It seems that there is constant edging along the entire arrow however this is not true In certain parts there is no difference in shading between outside background and arrow You perceive a ling because your visual system is filling in that in by using context This isn t happening in the eyes it is happening in the brain We fill in lines that aren t actually there Same with the black and white elephant 2 Illusory contour changes from one side of the contour to the other in the image a contour that is perceived even though nothing There is no arrow in the picture below and there are also no circles This is only what our brain perceives by using context and rules on what we know Our visual system is trying really hard to draw a line for the arrow and circles as if they are behind the arrow It is using good continuation so that the bottom left edge should be contiuous with the bottom right edge Also using occlusion the idea where something appears it is missing then we just assume that something is blocking occluding it We assume that the arrow is in front of the circle In reality all we are really seeing is a bunch of short lines and pac man shaped figures There is no arrow and no continuation of lines Why do you think the Gestalt school of thought was instrumental in identifying how we perceive images To answer this you need to know what Gestalt means 3 Gestalt grouping rules Rules describing which elements in an image will appear to group together Basically rules that help us determine what part of an image is together and what part is different and how those parts go together The original list was assembled by members of the Gestalt school of Grew out of failing of the structuralists who argued that perceptions are the sum of actions of sensation like a crystal is built of atoms thought Gestalt The whole is greater than the sum of its parts The thing that we see is more than just the sensation For example in the previous arrow picture they would say that the picture is more than some half black circles and lines That wasn t our perception that was only the sensation Trying to argue that the perception is exactly what we saw heard It is a faithful representation of the sensation One of the first things we learned about the visual system is actually that what we see is NOT accurate Gestalt school of thought The distinction between sensation and perception originates with the gestalt psychologists They are saying that the perception is not based only on what that sensation is It is based on more than just the retinal image Ex when you are hearing Starbucks lover in the song blank space but then you realize the lyrics say long list of ex lovers you cannot un hear the correct lyrics anymore The sensation stays the same but the perception changes One retinal image gives rise to MULTIPLE perceptions You want to think of sensation as a passive analytic process and perception as an active synthetic process Sensation To sense visual information we just have to have our eyes open We don t have to think hard or anything you just have to look It is also analytic meaning that once info comes in we start immediately breaking it down You have to work hard to see that cube in different orientations It is an active process It is also synthetic where we put all the pieces back together again Fourier synthesis is putting it back together again Perception Know the gestalt grouping principles good continuation occlusion texture segmentation similarity proximity connectedness common region how do those 4 latter 2 relate to proximity what trumps what parallelism symmetry Also know dynamic occlusion Good continuation Two lines will tend to group together if they seem to lie on the same contour Ex Consider the most left line Which one is most likely the best continuation of that line It would be the good bet line Our visual system doesn t make assumptions that it is all of a sudden bending to not likely It makes the better looking assumption that makes sense Color not equal In the image on the right you appear to see a circular shape in the middle kind of bean shaped You are using this perceptual grouping rule of good continuation to group them together and see the circle trumps good continuation as an organizing principle Here all things at The picture looks like an x with curly edges Once you see image B you see it as two separate threads crossing over each other Once you see image C you see two threads touching that are bent like a V Depending on the color we see different things Color is more important than good continuation 5 Texture segmentation properties that seem to go together Carving an image into regions of common texture Texture grouping can be based on similar color size orientation and aspects of form Ex in this picture there are bigger pieces on the top left and also the blue and green color differences stand out too You put together clues and we can look at this with out untrained eyes and still pick out certain pieces regions Parallelism they go together Lines that are parallel or symmetrical to each other usually look like Ex in the picture below lines 2 3 parallel to each other and 7 8 symmetrical look like they go together 6 Similarity chunks that are similar to each other are grouped together Basically things look similar asterisk vs octagon In the image below similarity is based on form overall shape each have 8 points The asterisk is distinct from octagon two categories with similar Ex Proximity Ex items
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