Figure 1: Angle of the E. lemming during one measurement (see Video 1) as calculated from the central differences of its positions. The estimated reaction times between the switching of the blue light and the reactions of the E. lemming are marked in the image. For the reaction delay between switch-on of the light and straight swimming we obtained Δt₁≈2.1s and Δt₂≈3.0s. For the delay between the switch-off of the blue light and start of tumbling it was only possible to estimate the time delay for the second light pulse, Δt₃≈2.4s. White background: blue light off. Light blue background: blue light on.