Shift of the beating field of vestibular nystagmus: an orientation strategy?

We investigated in humans whether the shift of the beating field, which is often observed during vestibular nystagmus, could be related to some strategy of orientation. Eye movements were measured with an infrared system during an experiment on self-motion perception in the dark. Subjects were asked to rotate, by means of a joystick, a mobile robot on which they were seated in order to reproduce a previously imposed passive rotation. We suggest that the shift of the ocular beating field is the manifestation of two different orientation strategies based on allocentric and egocentric reference frames, respectively. It is also proposed that subjects who preferably used the first strategy exhibited large shifts of the beating field, while the others who probably used egocentric memory did not exhibit any shift.