Fig. 2.

(A) Quantile probability plots for the two-choice data from experiment 1. The “x” symbols denote the data and the “o” symbols and lines represent the model predictions (see ref. 4 for further explanation). The plots show the 0.1, 0.3, 0.5, 0.7, and 0.9 quantile RTs (stacked curves) plotted against response proportion. Error data are shown for only one of the three levels of difficulty, because several subjects had zero errors in the other conditions (so quantiles cannot be computed). (B) Experimental and theoretical RT quantiles averaged over subjects for the one-choice data from experiment 1. The diagonal line has slope 1 and intercept 0. (C) Ratio of drift rate to SD in drift rate (v/η) plotted against independently derived alertness predictions for the data from experiment 2. (D) Proportion of performance lapses with RTs > 500 ms (Upper) and RTs > 1,500 ms (Lower) for the data from experiment 2, and corresponding model predictions. Each point represents data from a single subject for either the sleep-deprived or nondeprived conditions. The diagonal lines have slope 1 and intercept 0.