Human self-motion perception during translatory vestibular and proprioceptive stimulation.

Self-motion perception in space was studied in normal human subjects during passive vestibular stimulation (lateral translation of whole body in space), proprioceptive stimulation (of feet relative to trunk) and combinations thereof with the eyes closed. Stimulation was sinusoidal, +/- 10 cm, over a frequency range of 0.025-0.4 Hz. Vestibular self-motion perception became increasingly underestimated at low frequency, due to a rather high detection threshold. Proprioceptive stimulation at low frequency elicited a small self-motion illusion. During body translation relative to the stationary feet (vestibular-proprioceptive combination) the magnitude of perceived self-motion was constant across frequency and its threshold was low, as if determined by proprioception alone. Nevertheless, the results can be interpreted in terms of a vestibular-proprioceptive interaction, in analogy to previous findings for rotational stimuli.