August 2012
Volume 12, Issue 9
Vision Sciences Society Annual Meeting Abstract  |   August 2012
Observers can voluntarily shift their psychometric functions without losing sensitivity
Author Affiliations
  • Michael Morgan
    City University London, Max Planck Institute for Neurological Research, Cologne
  • Barbara Dillenburger
    Max Planck
  • Sabine Raphael
    Max Planck
  • Joshua A. Solomon
    City University
Journal of Vision August 2012, Vol.12, 1391. doi:
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      Michael Morgan, Barbara Dillenburger, Sabine Raphael, Joshua A. Solomon; Observers can voluntarily shift their psychometric functions without losing sensitivity. Journal of Vision 2012;12(9):1391. doi:

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

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Psychometric sensory discrimination functions are usually modeled by cumulative Gaussian functions with just two parameters, their central tendency and their slope. These correspond to Fechner’s “constant” and “variable” errors, respectively. Fechner pointed out that even the constant error could vary over space and time and could masquerade as variable error. We wondered whether observers could deliberately introduce a constant error into their performance without loss of precision. In three-dot vernier and bisection tasks with the method of single stimuli, observers were instructed to favour one of the two responses when unsure of their answer. The slope of the resulting psychometric function was not significantly changed, despite a significant change in central tendency. Similar results were obtained when altered feedback was used to induce bias. We inferred that observers can adopt artificial response criteria without any significant increase in criterion fluctuation. These findings have implications for some studies that have measured perceptual “illusions” by shifts in the psychometric functions of sophisticated observers.

Meeting abstract presented at VSS 2012


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