Vision Primary Visual Cortex Exam 5 Study Guide What are columns in cortex and how do the response properties of neurons in a given column compare to each other What are ocular dominance columns What is a hypercolumn o Columns all cells in a column respond to same type of stimulus neighboring columns respond to similar but not identical stimulus o Hypercolumn 2 sets of columns each covering every possible orientation 0 180 degrees with 1 set preferring input from the left eye and 1 set preferring input from the right eye 18 20 adjacent orientation columns o Orientation column all the cells in that column prefer same lines o Ocular dominance column prefers information from either left or right eye Understand the tilt aftereffect will look slanted o Stare at the diagonal lines then look at the straight ones and the straight ones Because cells that respond to the 20 and 20 degree lines became fatigued from staring upon a new stimulus the cells that were responding best were those to 10 or 20 and 10 and 20 so see image as tilted How does early experience play a role in the development of columns and of visual experience later in life o Critical period for development 1st 3 to 8 years in humans Cortical neurons are still wiring the visual system if one eye doesn t receive appropriate stimulation the neurons destined to respond to that eye don t become properly connected Vision Perceiving Recognizing Objects What is middle vision o A loosely defined stage of visual processing after basic features have been extracted from the image early vision before object recognition and scene understanding high level vision o Goal to organize elements of a visual scene into groups that we can recognize as objects a bunch of individual opinions hopefully emerging into one single answer o Summary Bring together that which should be brought together similarity proximity parallelism symmetry etc Split asunder that which should be split asunder edges that define regions figure ground relationships Use what you know 2D edges tell you about 3D corners or occlusion borders Avoid accidents accidental viewpoints Seek consensus and avoid ambiguity use committees to eliminate all but 1 possibility 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 o The distinction between sensation and perception originates with the Gestalt psychologists one retinal image gives rise to multiple perceptions the perception is greater than the sum of the sensation the whole is greater than the sum of parts o Sensation is a passive analytic process and perception is an active synthetic process Know the gestalt grouping principles good continuation occlusion texture segmentation similarity proximity connectedness common region how do those latter 2 relate to proximity what trumps what parallelism and symmetry Also know dynamic occlusion o Gestalt grouping rules a set of rules describing which elements in an image will appear to group together the whole perceptual world is more than the sum of its sensory parts Good continuation 2 lines will tend to group together if they seem to lie on the same contour 2 bits of an edge make it easier to perceive a 3rd line between them that isn t really there Occlusion if an edge seems to stop the visual system guesses that it is stopping because something else is in the way occluding it Dynamic occlusion when visual regions are discontinuous not only in space but over time something is moving behind objects but we still make sense of it Texture segmentation carving an image into regions of common texture properties texture grouping can be based on similar color size orientation aspects of form Similarity chunks that are similar to each other are grouped together Proximity items near each other are grouped together Connectedness if 2 items are connected they probably belong together Common region if 2 features appear to be part of the same common region they will group together Connectedness and common region trump proximity Parallelism symmetry lines go together that are parallel symmetrical How does color fit in to the gestalt grouping principles What is an ambiguous figure o When 2 cognitive demons shout equally loudly this is the exception that The rule there is usually consensus among committees o Ex the duck bunny pic you cant see both at the same time but you can see proves the rule both What is an accidental viewpoint not present in the world o a viewing position that produces some regularity in the visual image that is What is figure and ground and what principles do we use to decide which is which in a visual scene What is evidence that maybe object recognition precedes establishment of figure ground o Figure ground assignment is the process of determining that some regions of an image belong to a foreground object figure others are part of the background ground o Principles Surroundedness if 1 region is entirely surrounded by the other it is likely the figure Size smaller region is likely the figure Symmetry symmetrical region more likely the figure Parallelism regions with parallel contours are more likely seen as figure Relative motion how surface details move relative to an edge Synchrony elements that change at the same time group together Extremal edges shading of objects tell us about figure ground extremal edges are the set of surface points whose sight lines are tangent to the surface we perceive the thing with EE as closer to us What is the global superiority effect o Properties of the whole object take precedence over the properties of parts of the objects ex word made up of letters you see whole word before little letters making the letters o This is what middle vision does the 1st goal is to carve the retinal image into large scale objects Why do we probably not use templates to recognize objects o Templates matching pixel to pixel or feature to feature to something in memory view point would matter So we would need waaay too many templates What are geons What is recognition by components and what are some criticisms of this approach o Geons are geometric ions o Recognition by components objects are recognized by the identities relationships of component parts so we would only need to store 1 template o Criticism are geons really adequate enough for object recognition Ex cigar box vs books maybe no different geons needed you can change perspective without changing geons
View Full Document
Unlocking...