Human ocular torsion and perceived roll responses to linear acceleration.

We investigated if human ocular torsion (OT) and perceived roll (PR) are elicited in response to either dynamic interaural linear acceleration or dynamic roll tilt of the gravito-inertial force (GIF). We expanded a previous study [26] that measured only OT across a limited frequency-range (from 0.35 Hz to 1 Hz) by simultaneously measuring OT and PR at three very low (0.01, 0.02 and 0.05 Hz) and one high (1 Hz) frequencies. Three experimental conditions were investigated: (1) Y-Upright with acceleration along the interaural (Y) axis while upright, (2) Y-Supine with acceleration along the Y-axis while supine, and (3) Z-RED with acceleration along the rostro-caudal Z) axis with right-ear-down (RED). OT was measured by video-oculography, while PR was measured by use of a somatosensory bar. OT and PR were qualitatively different. Large OT responses were measured for Y-Upright and Y-Supine, while large perceived roll responses were observed for Y-Upright and Z-RED. OT for Z-RED was small, and PR for Y-Supine was absent. In conclusion, OT and PR appear governed by qualitatively different neural mechanisms. OT appears mostly influenced by central low-pass filtering of interaural graviceptor cues, while PR appears mostly influenced by roll tilt of the GIF.