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Form Perception Form perception 1 Structuralism Complex mental processes are created by combining fundamental components. Tichener, 19th Century. In other words, perception is an aggregate of simple elements. Eventually more than 40,000 "elementary sensations" were listed. 2 3 Gestalt ideas of form perception Founder of Gestalt Psychology is Max Wertheimer Wikipedia 4 Gestalt principles of organization (how figural properties determine perceived patterns): grouping due to proximity grouping due to similarity grouping due to common motion closure figure-ground perception A central tenet: The whole is different from the sum of its parts 5 Grouping by proximity A B C Image by MIT OpenCourseWare. 6 Grouping by shape Image by MIT OpenCourseWare. 7 Three general theories of form perception: 1. Form perception is accomplished by neurons that respond selectively to line segmens of different orientation. 2. Form perception is accomplished by spatial mapping of the visual scene onto visual cortex. 3. Form perception is accomplished by virtue of Fourier analysis. 8 1. Orientation of line segments and spatial frequency 9 Form perception with little information about orientation of line segments Image removed due to copyright restrictions. 10 Proof that low spatial-frequency information is used for face recognition Image removed due to copyright restrictions. 11 Image removed due to copyright restrictions. 12 Image removed due to copyright restrictions. 13 2. Topographic mapping 14 extreme isomorphism 15 Cortical layout of neurons activated by arrows 7 90 6 45 5 4 3 2 1 all arrows in visual field 0 0 contralateral hemifield -45 -45 -90 -90 -45 monkey area V1 0 45 0.25 0.25 0.5 0.5 1 90 1 2 2 4 7 7 4 Image by MIT OpenCourseWare. 16 Cortical layout of neurons activated by arrows 7 90 6 45 5 45 4 3 2 arrows across visual field 1 midline 0 0 -45 -45 -90 -90 -45 monkey area V1 0 45 0.25 0.25 0.5 0.5 1 90 1 2 2 4 7 7 4 Image by MIT OpenCourseWare. 17 File: prosthetics14 Cortical layout of neurons activated by a circle 90 Visual field 90 5 5 135 4 45 135 4 45 3 3 2 2 1 1 180 0 180 0 225 315 225 315 270 270 Posterior view of monkey brain showing the striate cortex and activated regions 5 4 5 4 3 4 5 3 3 4 5 3 2 270 2 2 270 2 1 270 1 1 270 1 315 225 315 225 0 180 0 180 45 135 45 135 90 90 90 90 left hemisphere 10 mm right hemisphere left hemisphere 10 mm right hemisphere Figure 5B, C. Schiller, Peter H., and Edward J. Tehovnik. "Visual Prosthesis." Perception 37, no. 10 (2008): 1529. Courtesy of Pion Ltd. Used with permission. 18 The Giotto Story: When Pope Benedict, the 12th, in 13th Century set out to have the walls of the great cathedral of St. Peter redecorated, he sent messengers all over Italy to find out who were the best painters. Specimen were gladly given. When a messenger came to Ambrogio Bondone Giotto (1267-1337), he did not provide a sample painting. Instead, he took a sheet of paper and a pencil dipped in red color, and drew a perfect circle. "Here is your drawing," he said. The Pope, upon examining all the productions submitted, chose Giotto without hesitation. To this day in Tuscany there is the saying: The round O of Giotto 19 C D A B G H E F I K M L Image by MIT OpenCourseWare. 20 3. Spatial frequency analysis Fergus Campbell and John Robson 21 deLange functions Spatial Frequency (cycles/degree) 0.1 1 10 100 0.001 1,000 INVISIBLE Sensitivity(1/thresholdcontrast) 0.01 100 VISIBLE 0.1 10 Threshold Contrast 1.0 1 0.1 1 10 100 Spatial Frequency (cycles/mm on retina) Image by MIT OpenCourseWare. 22 Generating compound gratings from a set of simple ones simple gratings compound graings compound graings at low contrast 23 Frequency-specific adaptation 24 Frequency-specific adaptation Contrast Sensitivity(1/ThresholdContrast) 1,000 1,000 100 100 10 10 Contrast Sensitivity (1/Threshold Contrast) 1 1 Spatial Frequency Frequency specific adaptation Image by MIT OpenCourseWare. 25 Channel model 0.001 Sensitivity of a 1,000 Single Channel Contrast Sensitivity(1/thresholdcontrast) 0.01 100 Threshold Contrast 0.1 10 1 1 0.1 1 10 100 Spatial Frequency (cycles/degree) CHANNEL MODEL Image by MIT OpenCourseWare. 26 Four essential properties of spatial frequency analysis: spatial frequency contrast orientation phase When information about these four properties is available, one can reconstruct any visual pattern 27 Shape-selective responses in inferotemporal cortex 28 IT neuron response to various shapes CELL 1 5o A B C D 1 -.01* -.04* .44* MO 03124 E F G H 20i/s .09* .20* .31* .15* 5s Image by MIT OpenCourseWare. 29 IT neuron response to various shapes CELL1 5o A B C D 1 .12* .32* .89* SU 0162 E F G H .09* .03* .15* .36* 10i/s 5s Image by MIT OpenCourseWare. 30 Image by MIT OpenCourseWare. 31 Intermediate level vision 32 Basic visual capacities color brightness pattern texture motion depth Intermediate visual capacities constancy selection recognition transposition and invariance comparison location 33 Transposition and invariance 34 Hirschfeld Image removed due to copyright restrictions. 35 Image removed due to copyright restrictions. 36 Image removed due to copyright restrictions. Voltaire, 18th French Enlightment writer of more than 2,000 books and pamphlets 37 The Art World Secret Knowledge by David Hockney 38 Masolino da Panicale, 1425 Robert Campin, 1430 Images are in the public domain. 39 Image by MIT OpenCourseWare. Camera obscura 40 Jan van Eyck 1436 Painting is in public domain. 41 Bacchus, c1597 by Caravaggio Camera obscura??? Painting is in public domain. David Hockney 42 original image camera obscura image rotated camera obscura image Painting is in public domain. 43 The marriage of Giovanni Arnolfini with Giovanna Cenami Jan van Eyck, 1434 C4amera obscura??? David Hockney Painting is in public domain. 44 The recognition of faces 45 The recognition of faces Photos removed due to copyright restrictions. 46 The recognition of faces Photos removed due to copyright restrictions. 47 The perception of subjective contours 48 49 50 51 A B Subjective contours at high contrast Subjective contours at isoluminance Image by MIT OpenCourseWare. 52 Response to subjective contours in V2 UNIT 3GD5 + A 27.7 B 4.6 Image by MIT OpenCourseWare. 53 Response to subjective contours in V2 A B 0.5s (20) (A) (B) Image by MIT OpenCourseWare. 54 The effects of V4 and MT lesions on intermediate vision 55 Match to sample task 56 The effect of V4 lesions on object matching Figure removed due to copyright restrictions. 57 Intermediate vision tasks SIZE A B C OCCLUSION A B C CONTOUR A B C 58 The effect of V4 lesions on object transformations Figure removed due to copyright restrictions. 59 Greater and lesser brightness discrimination Target Brighter Target D immer 60 Brightness discrimination, greater and lesser targets Figure removed due to copyright restrictions. 61 Greater and lesser size discrimination Target Larger Target S maller 62 Size discrimination, greater and lesser targets Figure removed due to copyright restrictions. 63 Confusing and interesting percepts created by great artists 64 Courtesy of The M. C. Escher Company, B. V. Used with permission. Maurits Cornelis Escher (b. 1898) 65 Courtesy of The M. C. Escher Company, B. V. Used with permission. 66 Courtesy of The M. C. Escher Company, B. V. Used with permission. 67 Summary, form: 1. Three theories of form precessing in the brain are (a) analysis by orientation of line segmens, (b) spatial mapping onto a topographically organized brain region and (c) Fourier analysis. 2. Areas V2, V4 and IT play important roles in intermediate vision. 3. Neurons responding to subjective contours have been found in V2. 4. Recognition of objects transformed in various ways is compromised by V4 and IT lesions. V4 lesions also produce major deficits in visual learning and in selecting "lesser" stimuli. 5. Some IT neurons are selective for objects including faces, but most respond to a variety of objects whose recognition is based on the differential activity of a great many neurons. 6. How we process and deal with ambiguities in perception remains a mystery 68 MIT OpenCourseWare http://ocw.mit.edu 9.04 Neural Basis of Vision and Audition Fall 2013 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms..
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