Optokinetic eye and head movements in the unrestrained cat.

Eye and head movements of the unrestrained and alert cat were measured with the search coil technique. Optokinetic responses were elicited by a moving random dot pattern. With the head free, slow phase gaze velocity (SPGV) during optokinetic nystagmus (OKN) was not faster than slow phase eye velocity (SPEV) with the head fixed neither with binocular nor with monocular stimulation. Cats with the head free also showed a directional asymmetry of SPGV during monocular stimulation with higher gain values for slow phases from temporal to nasal as compared to slow phases from nasal to temporal. Eye, head and body movements contributed to SPGV to a varying degree. Although SPGV remained rather constant (comparable to the head-fixed condition), the relative contributions of head velocity and eye velocity could fluctuate strongly. During the resetting saccades, the head ended its fast phase later than the eye (102 +/- 46 ms). During this period, the eye compensated the remaining part of the fast phase of the head and simultaneously executed an already new slow phase of gaze. It is discussed whether the cerebellar flocculus might provide a system to achieve constant gaze during OKN.