Rapid Ca²⁺ decay reverses sign of path curvature. (A) Mean Ca²⁺ signal elicited by release of caged cGMP (n = 7) by one (red) or two (blue) identical flashes 800 ms apart. (B) Time course of the mean path curvature for cells stimulated with a single flash (red, n = 11) or two flashes (blue, n = 16). (C) Mean dF_r/dt calculated from data in A for one (red) or two (blue) identical flashes. (A–C) The UV flashes are indicated by black dashed lines. (D) Superposition of single-cell trajectories (light blue, n = 17) and mean trajectory (dark blue) around the position where the second stimulus was delivered (yellow boxes). (E) Superposition of single-cell trajectories (light red, n = 11) and mean trajectory (dark red) around the same time point position as in D for those cells receiving only one stimulus. (F) Comparison of mean swimming paths for cells stimulated with a single flash (red, n = 11) or two flashes (blue, n = 17). The error at each point is represented by an ellipse with minor and major axes showing the SEM in the direction of the abscissa and the ordinate.