Sw. Wade et Is. Curthoys, THE EFFECT OF OCULAR TORSIONAL POSITION ON PERCEPTION OF THE ROLL-TILT OF VISUAL-STIMULI, Vision research, 37(8), 1997, pp. 1071-1078
Perceived postural orientation during whole-body roll-tilt is commonly
inferred from settings of a visual line to the perceived gravitationa
l horizontal or vertical. This inference assumes that the change in oc
ular torsional position (ocular counterrolling) which occurs during ro
ll-tilt has no effect on the perceived orientation of the visual stimu
lus. We investigated this assumption by measuring, during whole body r
oll-tilt stimulation, settings of a visual line and a somatosensory ba
r to the perceived gravitational horizontal and comparing the differen
ce in these settings to the objectively measured ocular torsional posi
tion for each subject. Two stimulus paradigms were used: one where the
subject was given a roll-tilt stimulus and the eye torted, the other
where there was eye torsion without a roll-tilt stimulus. In both para
digms there was a very close relationship in magnitude and direction b
etween the difference in the settings of the two perceptual indicators
to gravitational horizontal and the objectively measured ocular torsi
on. We conclude that change in ocular torsional position alone changes
the perceived orientation of a visual line. The corollary is that set
tings of a visual line cannot be used to infer perceived postural orie
ntation directly. (C) 1997 Elsevier Science Ltd.