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Figure 3: Demonstrative threshold-versus-contrast (TvC) curves for detection of a target consisting of a sine-wave grating in the presence of noise or sine-wave-grating masks. The horizontal axis denotes the contrast of the mask; the vertical axis denotes the contrast of the target (relative to the contrast threshold for detecting the target in the unmasked condition). Note that learning effects have been shown to lower the slopes of the TvC curves [90].