Swimming speed after a dark-light switch, depending on the swimming direction. (a) The relative swimming speed of the spheroids was plotted against the time after the light was turned on (vertical setup A). The swimming speed immediately before light stimulation was set to 100%. The swimming direction relative to the light source immediately before light stimulation was recorded and assigned to different sectors (a-i), and the color assignment is indicated. Each sector was analyzed separately. In addition, the average values for all directions are given (bold red line). Error bars refer to the standard deviation of the y-value (n = 20). (b) The swimming direction relative to the light source immediately before light stimulation was recorded and assigned to different sectors (gray arrows, a-i). The absolute swimming speed of the spheroids is shown for 0-4 s after the light was turned on (vertical setup A). All swimming speeds were plotted against the swimming direction immediately before light stimulation. The color assignment, the direction of the light vector, and the direction of the gravity vector are indicated. Reading from the inside outward, the gray concentric circles indicate 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, and 1.6 mm s-1. (c) and (d) The typical tracks of spheroids after a dark-light switch. The tracks were aligned relative to the moment of the dark-light switch (vertical lines), and the indicated color assignment reflects the time before and after the dark-light switch. (c) Tracks from vertical setup A, with the sinking depth of spheroids right after the dark-light switch indicated (in mm). (d) Tracks from horizontal setup B. (a)-(d) The yellow arrows indicate the light source. The light intensity was 2.1 μmol m-2 s-1 (intensities up to 457 μmol m-2 s-1 produced the same results).