SR responses for the three different input signals utilized. Note that SR decreases as the frequency of the input signal moves from the high-energy area of the noise spectrum to an area of less energy. At frequencies where the noise contains almost no energy, SR is negligible. (a) spectra of the noise and of the three input signals utilized. (b) Coefficient of correlation between the mean firing rate and the input signal at different noise intensities for the three input signals which spectra are shown on (a).