Fig. 8. Average parameters based on different parts of tracks (compare with Fig. 6). Thin lines correspond to data based on the four-point track fragments from frames 4–6, 6–9, 9–12 of the bursts; thicker lines correspond to frames 12–15, 15–18, 18–21 (boldest). Observe that the three thin lines indicating mean velocities almost coincide, i.e. the photokinetic response starts to develop around 10 s after the laser is switched on. The symbols correspond to the average parameters measured in the runs with laser intensity ten times higher than in the standard experiments.