Sensory Integration model of roll tilt perception

We investigated the effect of roll rotational visual cues on tilt perception in sensory conflict condition. Subjects participated in three test sessions that consisted of two different body constraint conditions: 1) free sway and 2) body strapped condition. Subjects were instructed to maintain upright posture in response to visual stimulus applied by three 19 inch LCD monitors located in front and either side of the subject. Computer-controlled sinusoidal visual stimulus provided randomly ordered roll rotational cues with peak velocity of 13.2 deg/sec over the stimulus frequency ranging from 0.01 Hz to 0.7 Hz. Trials for the stimulus frequency from 0.05 to 0.7 Hz lasted for 3 minutes, while those for lower stimulus frequency such as 0.02 and 0.01 Hz lasted for 5 and 7 minutes, respectively. While maintaining upright posture, subjects performed somatosensory bar task to indicate their perceived roll tilt. Results showed that significant roll tilt perception was observed without body sway for most of the subjects, but with delayed onset and temporal irregularity. This implies the CNS performs continuous sensory re-weighting in resolving sensory conflict.