Variability in the activation threshold enhances bimodality in the output signal y. (a-c) A fixed input-output response curve was considered. (d-f) Variability in the activation threshold was introduced. (g-i) Additional variability in the saturation level of the response curve was considered. The simulation details are exactly the same except that the sample size was 104 and, for the Gamma distribution, the value of a was 100 (refer to Figure 1 legend). The variability in the activation threshold and the saturation level was generated from normal distributions.