LCS 11: Cognitive Science 1. Gestalt principles 2. Recognition by - PowerPoint PPT Presentation

Agenda Pomona College ֠ Object perception LCS 11: Cognitive Science 1. Gestalt principles 2. Recognition by components theory Object recognition 3. Hoffman’s transversal intersection ֠ Presentation signup sheet Jesse A. Harris ֠ Reading for Wednesday: Hoffman, 1998: ch 5 ֠ Radiolab podcast (optional, but awesome) April 28, 2013 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 1 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 2 What is this? What is this? I challenge you to tell I challenge you to tell me: me: 1. What is its 1. What is its purpose? purpose? 2. Where does it come 2. Where does it come from? from? 3. What is the name 3. What is the name for this type of for this type of object? object? http://marksvegplot.blogspot.com/2010/12/identify-mystery-object.html http://marksvegplot.blogspot.com/2010/12/identify-mystery-object.html Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 3 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 4

Guesses What is this? Hazel Mystery object revealed: Salt? Snuff? Spittoon? Holder for some rare spice from the 1. It is used for Spice Islands? Finger bowl? Hard to tell how big it is. DRINKING millet Sherie Buck beer. I think it is old, not something you can go and buy now? Spice 2. It comes from crusher of some sort? NEPAL. Sherie Buck 3. It is called a Does it hold insects? TONGBA. Kim Swins http://marksvegplot.blogspot.com/2010/12/identify-mystery-object.html Is it a Bento Box? They are japanese lunch boxes. Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 5 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 6 What is this? Object recognition What makes object recognition complex? What really basic The problem of perceptual segregation: questions were NOT 1. Massive overlap in environment – where does one object asked? stop and another one begin? 1. Where is the 2. Objects of the same type vary in characteristics – on object? what basis do we categorize them as the same? 2. What are its parts? 3. Objects perceived as the same, despite differences in viewing – how are we able to account for viewpoint? http://marksvegplot.blogspot.com/2010/12/identify-mystery-object.html Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 7 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 8

Massive overlap in environment – where does one object stop Objects of the same type vary in characteristics – on what and another one begin? basis do we categorize them as the same? Gestalt psychology Fundamental principle of Prägnanz We tend to perceive and experience the world as regular, orderly, symmetric, and simple. Of several geometrically possible organizations [the] one [that] will remain will actually occur which possess the best, simplest, and most stable shape. (Koffka, 1935) Objects perceived as the same, despite differences in viewing – how are we able to account for viewpoint? Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 12

Proximity Gestalt psychology Fundamental principle of Prägnanz We tend to perceive and experience the world as regular, orderly, symmetric, and simple. Gestalt laws Reconstruct and reify objects according to several principles, including: Proximity Group nearby things as one. Similarity Group similar elements together. Continuation Avoid disrupting straight or smoothly curving lines. Closure Fill in missing parts if need be. Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 13 Similarity Similarity

Continuation Continuation Closure Closure

Closure Figure/ground Models of object perception Deriving shape information 1. Primal sketch Makes available basic features ◮ Early selectivity such as blobs, edges, groups, ◮ Three stages of representation stereopsis, and boundaries to derive shape information 2. 2.5 sketch ◮ Transform primitive features of Inferences about orientation, the objective stimulus to a depth, basic relationships figure in 3D space between features and objects ◮ Object-centered representation inferred transformed to viewer-centric 3. 3D model representation representation Components of object Published 1982 represented in “volumetric” and Published 1982 shape primitives. Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 23 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 24

Biedermann’s 1987 component geons 3D representation 36 fundamental geon types were originally proposed. Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 25 Biedermann’s 1987 Recognition-by-components Viewpoint invariance Major prediction of theory is that we consult geons in a Edge extraction viewpoint invariant representation. Early stage sensitive to surface characteristics, like luminosity Familiar objects (Biedermann & Gerhardstein 1993) Deletion of non-accidental properties ◮ Orientation didn’t a ff ect priming e ff ect of familiar 1. Extract invariants, like curvature, parallelism, symmetry. objects. 2. Construct geons Unfamiliar objects (Tarr and colleagues) Parsing concavity ◮ Novel objects show viewpoint dependence, but Attend to concave joints, as in Hoffman performance improves over time. Components + match ◮ Performance dependent on object type: speed increases Determine components and match to object representations. with expertise, but accuracy still viewpoint sensitive Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 27 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 28

Greebles Transversal intersection Concave crease Sharp edges pointing into object (vs. convex creases, which point out ) Can tell where arbitrary shapes interpenetrate by concave crease at surface. Rule of concave creases. Divide shapes into parts along concave creases. http://www.tarrlab.org Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 30 Transversal intersection Boundaries Which side of a curve corresponds to Minima rule. the object (figure)? Divide shapes into parts at negative Check both sides of curve and minima , along lines of curvature of choose the figure leading to a the principal curvature (where recognizable object. curvature grows least). Salient boundaries Gradient relationships Choose figure and ground so that the The more evidence you have for figure has the more salient transversal intersections, the easier boundaries. they are to spot. Evidence includes Salient parts salience of cusp boundary in accordance with sharpness of cusp Choose figure and ground so that the angle (Rules 17, 18) figure has the more salient parts. Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 31 Jesse A. Harris: LCS 11: Cognitive Science, Object recognition 32

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