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Andrew Haun, Edward Essock; Parameterization of contrast detection and discrimination in 1/f noise. Journal of Vision 2009;9(8):1005. doi: https://doi.org/10.1167/9.8.1005.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast sensitivity for a pattern in the presence of broadband 1/f spatial structure appears to be qualitatively different than would be predicted on the basis of established properties of contrast sensitivity measured using isolated, narrowband patterns. The effect of pattern orientation is different, with horizontal effects obtained at particular spatial frequencies rather than oblique effects, and the peak of the contrast sensitivity function is shifted towards higher spatial frequencies (Haun and Essock VSS 2008). In this experiment, threshold-versus-contrast functions were measured for oriented, 1.5 octave bands of spatial noise either against a mean luminance background, or against a background of broadband 1/f noise which did not include the target band frequencies and orientations. Seven central spatial frequencies and four central orientations were included. The effect of 1/f noise on the parameters of the familiar d' function for contrast detection and discrimination was measured. Sensitivity differences, with or without masking noise, are carried by anisotropies in the semi-saturation constants, the detection exponents of the d' function, and the height of the function. The effect of a 1/f noise mask on sensitivity is largely localized to an increase in the semi-saturation constant, though at lower spatial frequencies increased channel uncertainty and increased susceptibility to stimulus noise might also play a significant role in elevating thresholds, this influence measurable in the low-contrast exponent of the d' function: therefore several approaches must be considered in modeling the data. Suprathreshold parameters, including the height of the d' function and the compressive high-contrast exponent, appear to be unaffected by the presence of 1/f noise.
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