grouping in object recognition
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Paper reportTRANSCRIPT
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Grouping in object recognition: The role of a Gestalt law in letter identification
Pelli, Denis G., Majaj, Najib J., Raizman, Noah, Christian, Christopher J., Kim, Edward & Palomares, Melanie C. (2009).
Psychology and Neural Science, New York University, New York, NY, USA.
Cognitive Neuropsychology, 26 (1), 36-49.
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Gestalt Law
Grouping(proximity)
Most are binary discrimination tasks in the past
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Binary discrimination task
Differs from ordinary object recognition task
Quick Familiar Meaningful Named
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A well-known example from speech perception
• Hard task ABX (ABA or ABB)
• Simple task X (A or B)
The Difference on voice onset time in ABX task is much more noticeable
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• Simple X(A or B) task light memory load
• Hard ABX task higher memory load.
The simple one Less noticeableThe hard one more noticeable
Difference for voice onset time
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Grouping effects categorized object recognition
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To study object recognization
Study letter recognition
Identify snake letter
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Independent Variables : wiggle
Dependent Variables : Efficiency
based on the snake on the grass
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Wiggle The angle of sinusoid with the axis
Rotating Offsetting Phase shifting
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• To measure the relatively efficiency of recognition
• Use computer program to set an ideal observer ,as a reference for human performance on a absolute scale.
Geisler, 1989
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Measure the threshold contrast for 82% correct identification, both Human and Ideal observer.
• Compute contrast energy at threshold, integrated square of the contrast function
so the efficiency and energy are proportional to squared contrast
First proposed by Watson & Pelli, 1983
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Human observer
• Two undergraduate observer
• More data each observer
Use the concept akin to the method of psychophysics
Draw conclusion from individual, not averages
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Efficiency
To neglect Zero-noise threshold E0
Apply high background noise to elevate threshold E>>E0
E0 become relatively insignificant
Tanner, Birdsall(1958)
Pelli, Farell(1999)
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Zero wiggle Efficiency = 8%
At wiggle higher than 15o Efficiency
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Conclusion
• Wiggle raises human threshold, not ideal observer
• Gestalt laws play an important role in letter identification, and may be an evidence of its importance at ordinary object recognition.
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