Dynamic Effects on the Subjective Visual Vertical After Roll Rotation

Abstract

We investigated in normal human subjects how semicircular canal and otolith signals interact in the estimation of the subjective visual vertical after constant velocity or constant acceleration roll tilt. In the constant velocity paradigm, subjects were rotated in darkness at ±60°/s for five complete cycles before being stopped in one of seven orientations ranging from 0 to ±90° (right/left ear down). In the constant acceleration paradigm, subjects were rotated with an acceleration of +30 or −30°/s2 to the same seven end positions between −90 and +90°, by way of passing once through the upside-down position. The subjective visual vertical was assessed by measuring the setting of a luminous line that appeared at different test delays after stop rotation in otherwise complete darkness. The data suggest that gravitational jerk signals generated by otolith–semicircular canal interactions and/or carried by phasic otolith signals are responsible for the observed transient bias in the estimation of the subjective visual vertical. This transient bias depended on both rotation and tilt direction after constant velocity rotations, but was almost abolished following constant acceleration rotations.