Bimodal distribution in an output signal y due to cell-to-cell variability in an input signal x. (a) The input-output response curve is piecewise linear with a smooth junction at the activation threshold (between × = 30 and 40; black dots correspond to the case of the 'black' line in (b)). (b) The input signal × was assumed to satisfy the Gamma distribution. (c) Bimodal and even trimodal distributions in the output signal y appear as the cell-to-cell variability in × increases while its mean value is fixed. The distributions or histograms were obtained after transforming × to log(x). (d) Some of the bimodal distributions in (c) still appear in a linear scale. (e-h) A smaller mean value of × was used. Bimodal distributions, observed at the log-scale, were highly suppressed or disappeared in a linear scale. The sample size for the distributions was 105.