This slide shows one example of a stimulus presentation used measure the PRCs of male tree crickets. The male calls at his natural period, T_o, and is presented with a single perturbing stimulus. The natural period of the male is the average of his periods prior to the stimulus. The phase of the stimulus (f) is the time from the beginning of the chirp just prior to the stimulus to the beginning of the stimulus (t_stim) relative to the natural period (T_o). The phase change (Df) is measured in chirps subsequent to the stimulus. Phase change (Df) is simply the difference in time between the actual start of a chirp and the start of that chirp that would be expected if the male had continued to call at its natural period, again normalized to the natural period, T_o. We typically measured the asymptotic phase change several cycles (t_n) after the stimulus when the oscillator (cricket) had returned to its natural period.