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Figure 1. (a) Probability distributions (A = noise, B = signal) of a detection task showing 4 levels of decision thresholds X1 – X4. Values of X < X1 correspond to the first rating category ("1"), X1 < X < X2 to the second ("2"), etc., and X > X4 to the last ("5"). (b) The resulting ROC curve, giving the true positive fraction (TPF) as a function of the false positive fraction (FPF). The four operating points corresponding to the four decision thresholds in (a) are given by the boxes in (b).
