June 2006
Volume 6, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   June 2006
Orientation discrimination threshold-as-a-function-of-size curves shift more dramatically with increased stimulus contrast at 0 than 10 degrees in the temporal visual field
Author Affiliations
  • Sharon L. Sally
    Department of Psychology, Concordia Univeristy, Montreal, Canada
  • Rick Gurnsey
    Department of Psychology, Concordia Univeristy, Montreal, Canada
Journal of Vision June 2006, Vol.6, 195. doi:10.1167/6.6.195
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      Sharon L. Sally, Rick Gurnsey; Orientation discrimination threshold-as-a-function-of-size curves shift more dramatically with increased stimulus contrast at 0 than 10 degrees in the temporal visual field. Journal of Vision 2006;6(6):195. doi: 10.1167/6.6.195.

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

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Abstract

PURPOSE. Performance on many tasks can often be made equal across the visual field by appropriate scaling (F) of stimuli at all eccentricities according to [F=1+E/E2], where E2 indicates the eccentricity at which the size of the stimulus must be doubled, relative to the foveal standard, to achieve equivalent performance. Sally and Gurnsey (2004, Vision Research) have noted that E2s are larger at near-detection-threshold levels of stimulus contrast. This situation would arise if there was a relatively greater change in orientation thresholds as a function of stimulus contrast at the fovea than in the periphery, perhaps owing contrast-dependent changes in receptive field structure.

METHODS. Stimuli were broadband line patterns of 2 different aspect ratios (width 2.75 and 11 percent of height) presented at a range of sizes (0.2 to 36 deg.) at 0 and 10 degrees in the temporal periphery. Orientation discrimination thresholds were obtained for all stimuli at 3 levels of Michelson contrast (3, 12 and 48%).

RESULTS. For each aspect ratio, E2s increased from about 2.5 deg. at 48% contrast to 6 deg. at 3% contrast. The critical line sizes marking the transition to asymptotic orientation thresholds at large stimulus sizes changed to a greater extent (factor of 1.3 to 2.3) with increasing stimulus contrast at the fovea than in the periphery.

CONCLUSIONS. Less spatial scaling is required to equate foveal and peripheral performance at low contrast; this is related to a greater overall change in orientation thresholds as a function of contrast at the fovea.

Sally, S. L. Gurnsey, R. (2006). Orientation discrimination threshold-as-a-function-of-size curves shift more dramatically with increased stimulus contrast at 0 than 10 degrees in the temporal visual field [Abstract]. Journal of Vision, 6(6):195, 195a, http://journalofvision.org/6/6/195/, doi:10.1167/6.6.195. [CrossRef]
Footnotes
 NSERC grants to Rick Gurnsey
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