May 2008
Volume 8, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   May 2008
Second-order mechanisms do not process contrast-modulated orientation information optimally
Author Affiliations
  • Lynn A. Olzak
    Department of Psychology, Miami University of Ohio
  • Patrick J. Hibbeler
    Department of Psychology, Miami University of Ohio
Journal of Vision May 2008, Vol.8, 279. doi:10.1167/8.6.279
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      Lynn A. Olzak, Patrick J. Hibbeler; Second-order mechanisms do not process contrast-modulated orientation information optimally. Journal of Vision 2008;8(6):279. doi: 10.1167/8.6.279.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

There is considerable argument over whether second-order mechanisms (those responding to changes in textural contrast, grain, or orientation when mean luminance is contrast) constitute a single class of mechanism or whether different mechanisms underlie the processing of different types of second-order patterns. There is also argument as to the relative sensitivity of first order mechanisms (responding to luminance-defined patterns) vs. second-order mechanisms. Regan (2000) argues that the relative sensitivity of first and second order mechanisms is comparable for all hyperacuity tasks, although his measurements were confined to orientation-defined second-order patterns. We previously measured spatial frequency, contrast, and orientation discrimination thresholds for contrast-modulated second-order patterns. Our initial results indicated that while spatial frequency and contrast thresholds were comparable to those obtained with luminance-defined patterns, orientation judgments were much worse and observers refused to continue the experiment. We have now re-measured orientation discrimination thresholds and find them to be on the order of 10x values obtained with first-order stimuli. Our results imply that the mechanisms mediating contrast-modulated, second-order judgments are a) not well-suited to mediate judgments about orientation ; b) considerably less sensitive to orientation than first-order mechanisms; and c) different mechanisms than those mediating orientation-modulated judgments. We conclude that an understanding of the second-order systems is by no means complete.

Olzak, L. A. Hibbeler, P. J. (2008). Second-order mechanisms do not process contrast-modulated orientation information optimally [Abstract]. Journal of Vision, 8(6):279, 279a, http://journalofvision.org/8/6/279/, doi:10.1167/8.6.279. [CrossRef]
Footnotes
 Supported by NIH Grant EY13953 to LAO.
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