Fig. 7. Effect of light and dark adaptation on dark-flash responses. (A) Kinetics of behavioral dark adaptation assessed by responsiveness to dark flashes. Light-adapted larvae were placed in darkness, then tested at a single time point after the onset of dark adaptation (N=5 groups each time point). A test consisted of restoring the original level of illumination (200 µW cm^–2) and assessing responsiveness to a series of 5 dark flash stimuli of 500 ms duration, with 30 s intervals between stimuli. No change in dark-flash responsiveness is seen after 3 min of dark adaptation; however, exposure to longer periods of constant darkness rapidly reduces dark-flash responsiveness so that by 30 min, responsiveness to dark flashes is almost completely lost. (B) Kinetics of behavioral light adaptation assessed by responsiveness to dark flashes. Responsiveness to dark flashes develops slowly after dark-adapted larvae are exposed to constant bright light, reaching a maximum 20 min after the beginning of light adaptation. After the onset of illumination (400 µW cm^–2), groups (N=9) were tested with a 1000 ms long dark flash every 2 min. Video recordings were taken during the dark flash to measure O-bend responses. (C) Light-adapted larvae adjust quickly to increases in illumination. Larvae were pre-adapted at 10 µW cm^–2 for at least 3 h, then shifted to 100 µW cm^–2 for the indicated intervals before being tested with a 1000 ms dim flash back to 10 µW cm^–2 (N=11 groups for each time point). After just 1 s of increased illumination, 25% of larvae respond to dim flashes with O-bend responses. Larvae reach maximal levels of responsiveness (70% of larvae, see Fig. 3D) to dim flashes after 100 s of sustained illumination.