Linear Interaction of Vestibular and Optokinetic Nystagmus

In humans interaction of a prior vestibular stimulus (chair acceleration for 10 s) with an immediately following optokinetic stimulus (full field stimulation) was quantitatively studied to determine the change of slow phase velocity (SPV) of nystagmus elicited by the addition of the optokinetic stimulus. This change was compared to the SPV during pure optokinetic stimulation on the basis of the magnitude of the optokinetic input (retinal image motion) at the onset of the optokinetic stimulus. When measured shortly (0.7s) after optokinetic stimulus onset visual vestibular interaction is in fact linear i.e. the optokinetic reflexes are as effective in changing SPV during vestibular nystagmus as with pure optokinetic stimulation. As the optokinetic stimulus affects the charge in the visual vestibular integrator interaction cannot be expected to be linear after longer intervals of optokinetic stimulation.