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.

► Seeing stationary objects require movement of images on the retina.
► We have found that leopard frogs do not detectibly move their eyes.
► Leopard frogs make discernible periodic head movements of up to 100 μm at about 2 Hz.
► These head movements are linked to the frogs’ buccal and lung breathing cycle.
► Such movements generate sufficient retinal image motion to see stationary objects.