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A Rorschach Test for Visual Classification StrategiesContemporary models of pattern, detection and discrimination often employ template matching, but there have been few direct tests of this proposition. Adopting a method developed by Ahumada, we have analyzed how human observers discriminate between two letters of the alphabet ('c' and 'x'). The stimulus consisted of a one degree tall letter plus a four degree field of static white noise, both displayed for 16 frames at a 67 Hz frame rate. Our font and display dimensions approximated those of Solomon and Pelli. The observer identified the letter presented. A QUEST staircase varied letter contrast to maintain a 75% correct rate. For each trial, we preserved the information required to reconstruct the noise field. Possible trial categories based on (signal, response) pairs are: (c,c), (c,x), (x,c), (x,x). Noise fields were averaged separately for each category, and a final classification image was obtained by averaging the four mean images after inverting the sign of categories in which x was the response. If the observer employs a template, it should be revealed in the classification image. The lowpass-filtered classification image derived from 2048 responses of one observer is shown here, along with the corresponding ideal template. An approximation to the ideal template can be seen appropriately located within the classification image. We have also simulated and will discuss the classification images expected from various discrimination models in this experimental context. The construction of classification images appears to be a powerful tool for studying classification strategies used by human observers. Like a Rorschach test, it surreptitiously discovers the inner desires of the visual system.
Document ID
20020039785
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Watson, Andrew B.
(NASA Ames Research Center Moffett Field, CA United States)
Rosenholtz, Ruth
(NASA Ames Research Center Moffett Field, CA United States)
Null, Cynthia H.
Date Acquired
August 20, 2013
Publication Date
January 1, 1996
Subject Category
Aerospace Medicine
Meeting Information
Meeting: Association for Research in Vision and Opthalmology Annual Meeting
Location: Fort Lauderdale, FL
Country: United States
Start Date: May 11, 1997
End Date: May 16, 1997
Funding Number(s)
PROJECT: RTOP 199-06-12-39
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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