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SymmetryDetecting Symmetry in a Random Background
Monica Cook
Bilateral Symmetry
Bilateral symmetry occurs in many objects and scenes.
Eiffel Tower
Brooklyn Bridge
Animals Faces
A Symmetric Target from our Experiment
Bilateral Symmetry
Symmetry could be important because:• Almost everything is symmetric• It directs or catches attention• It is important in object recognition and memory
Purpose
Hypothesis: Attention and fixation are drawn to symmetric areas.
Determine if symmetry can be detected quickly within a random background
Methods
Experiment 1: Target located along the horizontal meridian
Methods
Experiment 2: Target located at any location within the display
ASL 504 Remote Eye Tracker
• Participant positioned in a chin rest facing monitor
• A video camera captures the eye
• Pupil and corneal reflection used to determine eye position
• 17-point calibration target
Eye camera and infrared LED
Calibration Check
A participant looking through the 17-point calibration target after being calibrated.
Example Trial
After a video has been calibrated, it looks like this…
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Experiment 1: Results
Time to First Fixation Time to Response
10.0
5.0
0.0
Tim
e (s
ec)
Fixation on Symmetric Target
Conclusions: Experiment 1
• Symmetry sometimes detected at a glance
• Detection sometimes required a much longer search
• Fixated on the target but still hesitated to respond
• The further the target was from the center, the longer it took to be detected
Experiment 2: Results
NUMBER OF FIXATIONS BEFORE TARGET FIXATED
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Above/Below Left/Right Off Axis Near Off Axis FarSYMMETRY LOCATION
NUM
BER O
F F
IXATIONS
SLKPFCDASCNSCLGYAS
Average
NU
MB
ER
OF
FIX
AT
ION
S
Experiment 2: Results
If fixation was drawn to symmetrical areas, this graph would slope progressively downward until the target was found. The blue line below is a good example.
TRIAL 19 - J UST TO R AND ABOVE FIX
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
FIXATION NUMBER
CNS
DAS
PFC
SLK
DIS
TA
NC
E IN
PIX
EL
S
FIXATION NUMBER
Experiment 2: Results
TRIAL 21 - TO R AND ABOVE FIX
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FIXATION NUMBER
CNS
DAS
PFC
SLK
TRIAL 18 - TO R AND ABOVE FIX
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55
FIXATION NUMBER
CNS
DAS
PFC
SLK
However, graphs like these do not follow this pattern.
Conclusions: Experiment 2
• The closer the target is to the center, the more quickly it is found
• Occasionally, participants gradually fixated closer to the target - inconsistent
Why?
There may still be preconscious symmetry detection –
Accidental symmetry attracts fixations
Further Research
A symmetry detection algorithm has been developed to test this.
Symmetrical axis of target
The Next Step…
• Compare fixation locations with the algorithm output for each image
• If fixations line up with lighter areas:– Indicates eye movements guided by
symmetry – Explains why noise in the background is a
problem
Thanks!
Jeff Pelz and Andy Herbert
Joe Pow and Bob Callens
Sue, Brian, Meredith, and Chris
The Other High School Interns