A. Top, the nonlinearity output u(t) at low and high contrast. Second – fourth row, u(t) with the mean, standard deviation or skewness held constant, and the other statistics varied as in the control case. B. Gain as a function of contrast with the different statistics held constant, measured as the average occupancy of the resting state, R(t) (eq. 2). C. Top, the control with the mean, u(t) at low and high contrast. Second – fourth row, u(t) with standard deviation or skewness varying as in the control case, and with the other statistics held constant. D. Gain as a function of contrast with the different statistics changing alone.