Previous studies have shown that in patients with unilateral vestibula
r deafferentation (UVD) there is a close relationship between the chan
ge in ocular torsional position consequent on the UVD, and the visuall
y perceived orientation of short dim lines in an otherwise darkened ro
om (1). However that result may have been confounded because the UVD m
ay have affected both ocular torsion and sensory information about hea
d position re gravity which must be used in making the visual perceptu
al judgement. Therefore we have sought a means of testing the relation
ship between ocular torsional position and the visual perception of or
ientation which was not confounded by the possible effect of changes i
n perceived head position.