Influence of visual signals on the coordination of spontaneous eye and head movements in infant rabbits.

Horizontal angular movements of eye, head, and trunk were simultaneously recorded in spontaneously behaving unrestrained rabbits in the period after postnatal eye opening. The recordings were performed in daylight as well as in darkness. A crosscorrelation analysis of the velocities of eye in head and of head to trunk during periods of exploratory activity showed that the resulting crosscorrelation functions were mainly determined by the correlation of coupled saccadic movements of eye and head. Already at the end of the third postnatal week, the maxima of the crosscorrelation functions were higher and their time shifts were shorter for movements in light than for movements in darkness. These observations suggest that the stronger coupling of saccadic eye and head movement velocities in response to light reflects a light-induced increase in the activity of premotor neurons of the superior colliculus.