Effect of angular acceleration on the localization performance of a remembered target

Both the influence of a remembered "earth-fixed" target (RT) on the vestibulo-ocular reflex and the effect of "unilateral cold caloric vestibular stimulation" on the localization of a RT have previously been proved. As "unilateral caloric stimulation" is not a physiological stimulus, the aim of the present study was to analyze whether even physiological "bilateral vestibular stimulation" (rotation) is able to affect the RT position. The pointing error (PE) towards an RT both without and following angular acceleration was investigated in 24 healthy volunteers. Postrotatory nystagmus response was recorded by electronystagmography. Evaluation parameters were "nystagmus frequency", "total amplitude" and "velocity of the slow phase"; the horizontal and vertical PE. The fixation of an RT led to a significant reduction of about 28% in nystagmus amplitude compared to the test condition in darkness. "After rotatory stimulation" a systematic horizontal PE in the direction of the fast phase of the postrotatory nystagmus (direction of "illusory self-rotation") occurred and the magnitude of this PE increased significantly compared to the test situation "without vestibular stimulation", but showed only a non-uniform negative correlation with two of the nystagmus parameters. It has to be concluded that "after rotatory stimulation", in contrast to "unilateral cold caloric vestibular stimulation", the subjective sense of "illusory self-motion" leads to a horizontal PE in the direction of the nystagmus fast phases.