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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