[The spontaneous change in the optokinetic reactivity in lizards]

The optokinetik reactivity of lizards (Calotes versicolor Daud., Agamidae, Squamata) varies spontaneously within seconds. The animals follow the sinusoidal movement of a striped cylinder with head and eyes. Thereby the line of sight may follow exactly the pattern movement without angular slippage, or a slippage of various degree happens, or the animal does even not react at all. The optokinetic reactivity varies continuously and not stepwise. Both eyes may move independently. Accelerated smooth eye movements which overtake the speed pattern movement were observed. In optokinetic reactions the eyes take the bigger part of the angular movement than the head; in cases of vestibular stimulation the reverse is observed concerning the amplitude of the compensatory countermovement. Similar effects of variable optokinetic reactivity in other animals and in man depending on attention are discussed.