Fragmentary control of vestibuloocular responses.

Intact pigeons (n = 64) were rotated in the dark in the horizontal plane at different orientations relative to the axis of rotation. The overall patterns of changes in nystagmus of the eyes arising as a result of displacement of the otolith membranes in several directions were analyzed. In ten pigeons, all changes in nystagmus (type 1 general patterns) could be explained in terms of the dynamics of peripheral neuron activity and non-specific (identical for all combinations of interacting inputs) central influences. In the remaining pigeons, part of the change in nystagmus (type 2 general patterns) was associated with central influences which were not identical for different combinations of interacting inputs. Repeated unusual combinations of vestibular stimuli and subsequent treatment with Nembutal transformed type 2 general patterns into type 1 general patterns. These data provide evidence for the fragmentary control of eye movements, whereby there is selective (fragmentary) modification of only some (individually specific) combinations of canal and otolith signals out of the whole set of vestibuloocular responses arising in response to stimulation of paired vestibular inputs; modification is mediated by changes in the sign of otolith influences on the canal components of these responses.