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Robbe L. T. Goris, Peter Zaenen, Johan Wagemans; Some observations on contrast detection in noise. Journal of Vision 2008;8(9):4. doi: https://doi.org/10.1167/8.9.4.
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© ARVO (1962-2015); The Authors (2016-present)
The standard psychophysical model of our early visual system consists of a linear filter stage, followed by a nonlinearity and an internal noise source. If a rectification mechanism is introduced at the output of the linear filter stage, as has been suggested on some occasions, this model actually predicts that human performance in a classical contrast detection task might benefit from the addition of weak levels of noise. Here, this prediction was tested and confirmed in two contrast detection tasks. In Experiment 1, observers had to discriminate a low-contrast Gabor pattern from a blank. In Experiment 2, observers had to discriminate two low-contrast Gabor patterns identical on all dimensions, except for orientation (−45° vs. −45°). In both experiments, weak-to-modest levels of 2-D, white noise were added to the stimuli. Detection thresholds vary nonmonotonically with noise power, i.e., some noise levels improve contrast detection performance. Both simple uncertainty reduction and an energy discrimination strategy can be excluded as possible explanations for this effect. We present a quantitative model consistent with the effects and discuss the implications.
Note: Bold symbols and numbers indicate frozen parameter values.
*Indicates that D is outside the (Bonferroni corrected) 95% confidence interval of a stationary observer.
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