Voluntary suppression of caloric nystagmus under fixation of imaginary or after-image target.

Voluntary suppression of caloric nystagmus was investigated in 10 normal subjects under the following three conditions; i) with visible, earth-fixed target in the dark ("visual"), ii) with imaginary target in the dark ("imaginary"), and iii) an after-image on the fovea in the dark ("after-image") Subjects were able to suppress caloric nystagmus with a visible target very well, but they could only partially suppress caloric nystagmus with imaginary target and with after-image. The degree of suppression in the "imaginary" and "after-image" conditions was significantly less than that in "visual", but was not zero. These results are consistent with those of many reports about visual-vestibular interaction and VOR voluntary modification during rotation, and suggest that smooth pursuit eye movements (SPEM) system plays a major role in visual suppression during caloric nystagmus.