Head-centric visual localization with lateral body tilt

The aim of the present investigation was to decide whether subjects can correctly judge the head-centric orientation of a display in the dark in spite of the counterrolling of their eyes caused by head tilt. Four subjects were asked to set two luminous points orthogonally to the median plane of their heads, with head and body upright or tilted 90 degrees to the left or right side. The luminous points could be rotated in a frontal plane about a stationary fixation light situated straight ahead. Subjects viewed this display monocularly with either eye. In the same three body positions, ocular counterroll was determined photographically. The settings turned out to be neither accurately oculocentric nor head-centric, and there were considerable inter- and intrapersonal variances. However, on average, display adjustments were more head-centric: mean difference of ocular counterroll between left-ear-down and right-ear-down conditions was 13.2 deg, whereas the mean difference of the subjective head-centric orientations was only 3.8 deg.