Summary Pilots reflexively tilt heads toward horizon during VMC roll maneuvers. Head movement acts to stabilize retinal image. Generated by motion on retina, not vestibular. Stabilized horizon is the primary visual cue. Peripherally viewed cockpit structures secondary cues.
Secondary cues move with airframe.
Control movement compatible with secondary cues. Beyond 40 degrees decrease in head displacement, so pilots can not stabilize the horizon. Horizon acceleration, stabilization of secondary cues. Sudden switch may lead to false perceptions.