Leopard frogs move their heads, but not their eyes: implications for perception of stationary objects.

Movement of an image on the retina is necessary for the persistence of vision in vertebrates. Leopard frogs (Rana pipiens) do not show any obvious independent eye movements that could sustain perception of stationary objects when the animal itself is stationary. However, video recordings of normal, awake leopard frogs made through a dissecting microscope reveal that the animal's whole head oscillates with an amplitude of 10-100 μm in step with the breathing cycle. The retinal image shifts produced by these breathing movements could ensure continuous perception of the frog's stationary environment.