Elicitation of vestibular nystagmus by a step mode of horizontal linear acceleration

Elicitation of lateral nystagmus to linear acceleration in the interaural axis of the head was examined in 35 healthy subjects who were seated upright in darkness within the capsule (sled) of an accelerator. The motion stimulus was a step-mode oscillation of 0.3 G and 0.5 G at a distance of 10 m, though an additional 0.1 G stimulus was given in 10 subjects. The nystagmus was already fully elicited at 0.3 G in 13 subjects. In 9 of the remainder, however, the occurrence was newly developed or further improved at 0.5 G. When 10 subjects among the full-elicitation group at 0.3 G were examined at 0.1 G, only one subject still maintained high susceptibility. G-direction-dependent asymmetry was frequently observed in the nystagmus elicitation. Such directional preponderance was distinct at 0.3 G, but lessened at 0.5 G, when the subjects were examined whose nystagmus elicitation was very frequent. The results indicate that a greater G-load is more efficient for nystagmus elicitation, but may eliminate further chances to identify the response properties.