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.
Gestalt Law
Grouping(proximity)
Most are binary discrimination tasks in the past
Binary discrimination task
Differs from ordinary object recognition task
Quick Familiar Meaningful Named
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
• 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
Grouping effects categorized object recognition
To study object recognization
Study letter recognition
Identify snake letter
Independent Variables : wiggle
Dependent Variables : Efficiency
based on the snake on the grass
Wiggle The angle of sinusoid with the axis
Rotating Offsetting Phase shifting
• 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
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
Human observer
• Two undergraduate observer
• More data each observer
Use the concept akin to the method of psychophysics
Draw conclusion from individual, not averages
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)
Zero wiggle Efficiency = 8%
At wiggle higher than 15o Efficiency
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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