7/31/2017
• Outline
» Chap. 3
◊ Visual Perception
–
–
–
–
–
Unconscious inferences
Preattentive organization
Retinal vs. cortical effects
Gathering Visual information
Visual Sensory Memory
Study Questions.
Describe the unconscious inference theory of Helmholtz. How
does the theory explain some visual illusions?
Describe the gestaltist principles of grouping
Define visual sensory memory. How did Sperling empirically distinguish between a
capacity and a duration hypothesis.
Perception and Pattern Recognition
• Visual Perception
Perception and Pattern Recognition
• Visual Perception
Perception
• Perception is in the brain
» Melzak : “Pain is in the brain”
◊ Phantom limb pain
» Filling in the blind spot
» Complimentary colour mixing
» Visual illusions
◊ E.g., The moon illusion
◊ Other illusions
Perception
• The unconscious inference theory (helmholtz)
» Analyze cues in sensory input
» Construct a perception with depth, size and motion.
» Send perception on to conscious mind.
• The Müller-Lyer illusion
Perception
• Problems with the unconscious inference
explanation.
Perception
• The frame illusion
Perception
» Assimilation theory: We incorporate nearby elements into an
object’s boundary when assessing size.
Online Demo
Perception
• Size illusions based on linear perspective
Example 1
Chasing illusion
A great size constancy illusion: The power of persective
Shadow and ball illusion
Coding of Contrast and Contour
• Three examples of exaggerated contrast
Coding of Contrast and Contour
• Receptive fields and on-off areas
-
•
-
+
+
-
-
Contrast heightening
+
-
+
-
-
-
Hermann - Hering grid
• Receptive fields and the Hermann-Hering illusion
Gestalt Perception
• Sensation and bottom-up processing
• “The whole is greater than the sum of its parts”
-> Perception involves an interplay between bottom-up
and top-down processes.
• Context and top-down processing.
• Pitting the gestalt against sensation
• Illusions deriving from top-down processing
Gestal principles of grouping
• Proximity.
Gestal principles of grouping
• Similarity.
Gestal principles of grouping
• Closure.
Gestal principles of grouping
• Good continuation.
Online Demo
Figure/ground
• We divide a visual scene into figure (the object to
which we attend) and ground (background).
Example 1:
Example 2: Figure and Ground in MC
Escher’s art.
Example 3:
Rubin Vase by Shigeo Fukuda
Perception and Pattern Recognition
• Visual auras and migraine headaches
» Cortical or retinal?
◊ A retinal effect:
Perception and Pattern Recognition
• Visual auras and migraine headaches
» Cortical or retinal?
◊ A retinal effect:
◊ A cortical effect:
Perception and Pattern Recognition
• Extracting visual information
» Saccades - eye movements, which occur in a jerking,
start-stop fashion.
Perception and Pattern Recognition
• Visual sensory memory
» Visible persistence
» Selection from brief displays
H
L
B
M
Q
Y
X
S
E
T
W
R
F
Z
N
Q
W
U
C
D
R
Y
E
T
G
X
M
W
E
I
V
F
T
U
R
Y
Perception and Pattern Recognition
• Visual sensory memory
» Visible persistence
» Selection from brief displays
George Sperling
» Original findings
◊ Observers remember 4 or 5 items (span of apprehension)
◊ Sperling’s question: Where is the limitation?
– Capacity hypothesis: The visual system only registers 4 or 5 items
– Duration hypotheis: All the letters get registered but fade rapidly
◊ The partial report procedure
– E.g., Standing’s experiment
Perception and Pattern Recognition
• Visual sensory memory
Estimated # letters available
» Sperling’s results
10
8
6
4
2
0
0
.15
.30
Cue Delay (Seconds)
1.0
Full
Report
Perception and Pattern Recognition
• Visual sensory memory
» Visual Masking
» Averbach and Coriell (1961)
◊ Two types of cues: Bar markers and circles
◊ Partial report of 1 item.
J
T
Y S
V
P W N R
Q O M K
H
X I
J
T
Y S
V
P W N R
Q O M K
H
X I
Perception and Pattern Recognition
• Visual sensory memory
» Averbach and Coriell (1961)
Percentage Correct
100
80
60
Bar probe
40
Circle probe
20
0
-100
0
100
200
Cue Delay (ms)
300
400
500
Perception and Pattern Recognition
• Visual sensory memory
» Is selection from VSM precategorical?
◊ Merikle (1980)
◊ Demo
H
6
B
M
8
Y
X
S
E
7
W
9
Perception and Pattern Recognition
• Visual sensory memory
» Is selection from VSM precategorical?
◊ Merikle (1980)
◊ Demo
A
3
A
6
T
3
R
5
8
G
6
T
R
5
8
Absent
Present
Correlated physical dimension
G
Perception and Pattern Recognition
• Visual sensory memory
» Is selection from VSM precategorical?
◊ Merikle (1980)
◊ Demo
Partial
Whole
Correlated Physical Dimension
Present
Absent
6.4
5.5
4.4
4.2
Perception and Pattern Recognition
• Visual sensory memory
» Literal representation
◊ Template matching
Perception and Pattern Recognition
• Visual sensory memory
» Other issues
◊ Ecological validity