Response of the monostable switch module. X∗is shown in response to a smooth gradient signal (of the form a + bsinθ, with a maximum at θ = Π/2 ) for a (A) non-diffusible and (C) highly diffusible case and a localized signal input (of the form of a square pulse) for a (B) non-diffusible and (D) highly diffusible case. (A) The concentration profile of X∗is broader near the maxima and minima of the signal and it exhibits a spatial switch-like behaviour. (B) The spatial profile of X∗is qualitatively similar to the signal. (C,D) X∗is shown here for when X is highly diffusible (solid line) and non-diffusible (dashed line). (C) In response to the gradient signal, the spatial profile of X∗increases sharply in the region where the signal crosses a threshold value. Thus the diffusion of X leads to an enhancement of the spatial switch response. (D) For the localized signal, the spatial profile of X∗shows greater contrast when X is highly diffusible.