A comparison of the dynamics of the rabbit and human vestibulo-ocular reflex

We observed several differences between the dynamics of the vestibulo-ocular reflex (VOR) in rabbits and in human subjects. In the rabbit the "apparent time constant" (time required for the slow phase velocity to reach 37% of the initial value) of postrotatory nystagmus (PRN) increased and the low-frequency phase lead of sinusoidal perrotatory nystagmus decreased with increasing stimulus velocity. In human subjects these measurements did not change with stimulus velocity (for the range of 15 to 120 deg/s). The pattern of PRN decay in the rabbit usually appeared linear whereas in human subjects the decay was usually exponential. After the largest stimulus (120 deg/s) PRN reversals occurred in human subjects but not in rabbits. These differences can be explained on the basis of a simple nonlinearity (saturation of a feedback pathway) present in the rabbit but not in the human VOR.