several strange effects arising from perceptual grouping
TRANSCRIPT
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Several Strange Effects Arisingfrom Perceptual Grouping in Vision
Psychonomic Society
November 2002
James R. Pomerantz
Department of PsychologyRice University
Houston, Texas, USA
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AcknowledgmentsStudent Collaborators
Apu Agrawal Martha JeongAnna Ahrens Steve Jewell
Mia Cox Hana KhanCathy Carson Sandra Lozano
Ekanem Ebinne Jane PittsMary Portillo Edward Pristach
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Preview of Conclusions
By using stimuli with strong perceptualgrouping tendencies, we can take many
standard findings in visual perception and
stand them on their heads.
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Preview of Conclusions
• If we fail to take perceptual organization
into account, we can encounter some odd-looking results in our experiments.
• These odd results stem from a mismatch
between how the experimenter defines the
stimulus and how the perceiver organizes
the stimulus.
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What are the Familiar Findings?
1. Irrelevant or information-free ‘noise’ contexts hurt
2. Search slopes range from nearly flat to positive
3. Redundant information often helps, seldom hurts
4. When targets pop out, we know their location
5. When texture boundaries are apparent, we knowtheir correct location too
6. “Same” judgments are generally easy and fast
7. Incongruent flankers are almost always harmful8. Dual-task performance is at least as hard as single.
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Familiar Findings: Positive to
Flat Search Slopes
Very inefficient search>30 msec. / element
E.g., conjunction search
RT
Efficient search or popout
~ 0 msec. / element
E.g., vertical among horizontals
Display Size# elements in field
0 Many
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Familiar findings…
Incongruent Flankers Hurt
Task: Is center letter an X or an O?
X X X
O O O
X O X
O X O Eriksen & Eriksen, et al.
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Other Familiar Findings in Visual
Information Processing
• Irrelevant information hurts performance,unless it can be filtered out or unless it
boosts arousal, etc.
• Redundant information often helps
performance
• When a target pops out, its location isquickly and accurately known.
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Common Findings, continued
• Judging whether two things are the same or different is a basic process that is fast and
accurate.
• Attending to two stimuli at once is harder
than attending to just one.
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What are the Strange Effects?
1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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What are the Strange Effects?
1. Facilitation from information-free contexts
2. Steeply negative search slopes
3. Redundancy losses4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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Q: When does adding “noise” to adisplay improve performance?
A: When it produces emergentfeatures that lead to configural
superiority effects.
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Facilitation from Information-Free Contexts:
Configural Superiority Effects
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Configural Superiority, continued
Target Context
(all identical)
Composite
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Important Control:
Configural Inferiority Effects
Pomerantz, Sager, & Stoever, 1977
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Classes of CSEs
Familiar CSEs – line patterns
Line slope differences (e.g., arrows and triangles)
Line curvature differences (e.g., parentheses)
New CSEs – dot patterns
Dot orientationDot proximity
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Parentheses are just an example...
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A New CSE:Orientation
The bottom discrimination is
easier than the one in the upper
left, indicating another CSE, probably based on the emergent
feature of orientation.
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Another newCSE:
Proximity
Here, the same target dots
combine with shifted
context dots to create a
CSE based on dot proximity.
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Other CSEs…?
There are probably atleast a dozen CSEs
For illustrative purposes,the parenthesis pairswill be used, but theyare just a convenientexample.
Graphic from Pomerantz, OPAM 2001
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What are the Strange Effects?
1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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?
Steeply Negative Search SlopesDoubling the number of items in a display
from 16 to 32 reduces search time by ~1000 msec.
( ( ( (
( ( ( (( ( ) (
( ( ( (
( ( ( (
( ( ( (( ( ( (
( ( ( (
( ( ( (
( ( ( (( ( ( (
( ( ( (
( ( ( (
( ( ( (( ( ) (
( ( ( (
DS=16 Add 16 more
distractors
DS=32
Pomerantz, Sager, & Stoever, 1977
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Negative Search Slopes
Many
Display Size
# elements in field
RT
0
Very inefficient search
>30 msec. / element
E.g., conjunction search
Efficient search or popout
~ 0 msec. / element
E.g., vertical among horizontals
Steeply negative slopes,
nearly -200 msec. / element
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Causes of Negative Search Slopes• Grouping can lead to errors in reporting the
effective display size (e.g., reporting 32when we should report 16), but this cannot
change the sign of the slope.
• Thus, negative slopes are due to somethingelse, namely, emergent features.
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What are the Strange Effects?
1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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Redundancy Losses
Task 1: Control task, with second (right) channel of information irrelevant and uninformative:
Discriminate ( ) from ) )
Task 2: Correlated task, with information on second
channel redundant so stimuli should be “twice asdifferent”:
Discriminate ( ( from ) )
Result: Performance is worse on Task 2Pomerantz & Garner, 1973
h h ff
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What are the Strange Effects?
1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses
4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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Perverse (mislocalized) Pop Out
We have no problem here either spotting the odd
element or knowing where it is in the display.
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Question: What if the target item were to group
with one of the background items? What, if
anything, will pop out then?
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An example…
Here, mislocalization is common…
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Demonstration: Mislocalized pop out
In the following slides, call out quickly the
numerical position of the odd item. E.g.:
X O X => “2”
O X X => “1”, etc.
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A B A
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O X X
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$ $ &
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( ) (
What are the Strange Effects?
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What are the Strange Effects?
1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses
4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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5. Mislocalized texture boundaries
If an element at a texture boundary groupswith another element on the other side of
that boundary, that should lead to a
misperception of the boundary’s location.
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Spot the Texture Border
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Fairly easy task…
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Easy with color differences too…
Texture Borders with Grouping:
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Texture Borders with Grouping:
Problems Arise:
T t B d ith G i
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Texture Borders with Grouping:
Parenthesis Pairs
??
T t B d ith G i
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Texture Borders with Grouping:
Arrows & Triangles
Te t re Borders ith Gro ping:
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Texture Borders with Grouping:
Arrows & Triangles
Texture Borders with Grouping:
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Texture Borders with Grouping:
Arrows & Triangles
d i h i
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Texture Borders with Grouping: Ks
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Texture Borders with Grouping: Ks…
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What are the Strange Effects?
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g
1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses
4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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Missing flanker incongruity effectsWe find no flanker (‘Stroop’) interference with
parenthesis pairs:
in speeded classification tasks with one elementrelevant, responses to pairs incongruent neighbors
are no slower than with congruent:Congruent: ( ( and ) )
Incongruent: ( ) and ) (
Note: in contrast,Garner interference is very strong.
What are the Strange Effects?
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1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses
4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
Better dual- than single-task
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g
performanceCondensation (conjunction) task is easier than
filtering (feature) task with parentheses:
( (
( )
) (
) )
( ( ) ( ( (
( )
) (
) )( ) ) )
Harder Easier
Pomerantz & Pristach, 1989
What are the Strange Effects?
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1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses
4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
Spurious Sameness & Dubious Difference
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p
Idea: if two items are grouped perceptuallyinto one, it should be difficult for perceivers
to judge those items as same or different.Q: Same or different: “( )” ?
This could be a difficult task.Reason 1: there is only one thing
Reason 2: symmetry; convexity/concavity
Pilot data: The hypothesis may be right…
What are the Strange Effects?
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1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses
4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects
7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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Dimensional blindnessWith some multidimensional stimulus sets, it’s
hard to identify the underlying dimensions
XX OX
XO OO
Easy Easy Hard
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Dimensional blindnessEven color coding the rightmost panel fails to help:
the nominal dimensions are masked by emergent
features…
XX OX
XO OO
Easy Easy Hard
What are the Strange Effects?
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1. Facilitation from information-free contexts2. Steeply negative search slopes
3. Redundancy losses
4. Perverse (mislocalized) pop out
5. Mislocalized texture boundaries
6. Missing flanker incongruity effects7. Better dual- than single-task performance
8. Spurious sameness and dubious difference9. Dimensional blindness?
10. Underestimated numerosity?
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Underestimated numerosityKey idea:
If items in a display group into a singleconfiguration (or clusters of configurations),
then estimates of the number of elements inthe display should be systematically low.
Evidence: experiments not yet designed…
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Implications• Remembering the “Experience Error”
• Conducting and Reporting our Experiments
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The Stimulus and Experience ErrorsThe Stimulus and Experience ErrorsIn psychology we have often been warned againstthe stimulus error , i.e., against the danger of confusing our knowledge of the physicalconditions of sensory experience with thisexperience as such. As I see it, another mistake,which I propose to call the experience error , is
just as unfortunate. This error occurs when certaincharacteristics of sensory experience are
inadvertently attributed to the mosaic of stimuli”(Kohler 1929/47, p. 95).
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Implication: The Stimulus Error Implication: The Stimulus Error • Denying seeing stripes in the rainbow because
we know they are not there.• Confusing brightness with intensity, or
entering a room lit with one candle,illuminating a second candle, and reportingthat the room is now twice as bright.
The Experience Error The Experience Error
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pp
• Seeing stripes in the rainbow and
presuming they are actually there.• Similarly, believing that other
organization resides in the stimulus.• Often ignored today, but given
prominent mention in Palmer’s text.
The Experience Error The Experience Error
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pp
Presuming what the stimulus is:
• We experience a percept organizedinto regions, objects, and parts.
• We then assume this organization
exists in the distal world and isavailable in the proximal (retinal)
image, rather than having to becomputed.
A Possible Example of theA Possible Example of the
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Experience Error?Experience Error?Object-based Attention:
Easier reporting 2attributes of 1 object than
1 attribute of 2 objects.
Issue: Who says the box is
one object and the line
another?(From Duncan, 1984)
Easy Hard
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Why don’t we call the upper
component of the ‘box’one object, and the lower
another? Then there would
be two objects and no‘gaps’ at all!
What about Elements that Group?What about Elements that Group?
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Parenthesis Pairs
Group StronglySo Are They A Single
Object or Two Objects?
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Implication: The Design of StimuliImplication: The Design of Stimuli• Researchers in object perception must be as
careful as those in color vision not tomisrepresent the stimulus.
• Like ‘red’, ‘object’ is a psychologicalconcept.
• E.g., experimenters must distinguish how
many elements they say are in the targetarray from how many our perceivers see.
In ClosingIn Closing……
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g
• Not an overstatement to say it is our ‘dirtylittle secret’ that none of us knows what an
object is, or what a part or a feature is.• We often guess right, but we’re still guessing.
• Once we understand when and how groupingworks, we will better to know what objects,features, and parts are, and so better know how
attention is allocated to them.
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Thanks for Listening.