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
5
4
3
2
1
45
visual field
0
all arrows in
contralateral
hemifield
0
-45
-45
-90
-90
-45
monkey area V1
0
45
0.25
0.5
1
2
4
7
90
0.25
7
4
2
1
0.5
Image by MIT OpenCourseWare.
16
Cortical layout of neurons activated by arrows
7 90
6
5
4
3
2
1
45
visual field
45
arrows across
midline
0
0
-45
-45
-90
-90
-45
monkey area V1
0
45
0.25
0.5
1
2
4
7
90
0.25
7
4
2
1
0.5
Image by MIT OpenCourseWare.
17
Cortical layout of neurons activated by a circle
90
5
135
Visual field
3
90
5
45
4
4
135
2
1
0
180
270
1
4 5
270
5 4 3
2
1
1
2
3
4 5
270
270
315
225
315
0
180
0
135
45
10 mm
right hemisphere
2
1
225
135
90
90
left hemisphere
5 4
3
180
45
90
90
left hemisphere
315
225
Posterior view of monkey brain showing
the striate cortex and activated regions
270
270
0
180
315
225
3
45
3
2
1
2
File: prosthetics14
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
A
C
B
E
I
H
G
F
D
K
L
M
Image by MIT OpenCourseWare.
20
3. Spatial frequency analysis
Fergus Campbell and John Robson
21
deLange functions
Spatial Frequency (cycles/degree)
0.1
1
1,000
0.001
INVISIBLE
100
0.01
VISIBLE
0.1
10
1.0
Sensitivity (1/threshold contrast)
Threshold Contrast
100
10
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/Threshold Contrast)
1,000
100
100
10
10
1
1
Contrast Sensitivity (1/Threshold Contrast)
1,000
Spatial Frequency
Frequency specific adaptation
Image by MIT OpenCourseWare.
25
Channel model
Sensitivity of a
Single Channel
1,000
0.01
100
0.1
10
1
Contrast Sensitivity (1/threshold contrast)
Threshold Contrast
0.001
1
0.1
1
10
Spatial Frequency (cycles/degree)
100
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
o
5
A
B
1
C
-.01*
D
-.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
o
5
A
C
B
1
.12*
D
.32*
.89*
SU 0162
F
E
.09*
G
.03*
H
.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???
David Hockney
Painting is in public domain.
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
Subjective contours at high contrast
B
Subjective contours at isoluminance
Image by MIT OpenCourseWare.
52
Response to subjective contours in V2
UNIT 3GD5
27.7
4.6
+
A
B
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
A
SIZE
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 Dimmer
60
Brightness discrimination, greater and lesser targets
Figure removed due to copyright restrictions.
61
Greater and lesser size discrimination
Target Larger
Target Smaller
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.