Which visual illusion is caused by tall grass or similar textures that makes a pilot continuously input the flight controls?

• A. False Horizon
• B. Height/Depth Illusion
• C. Induced Motion
• D. Size/Distance Illusion

Answer: (C)

Dense ground texture from tall grass can create a misleading line that the eye interprets as the horizon. When your visual system locks onto that apparent horizon, you end up repeatedly adjusting the aircraft to stay “level” with it, even though the true horizon is elsewhere. This is a false horizon illusion—the ground texture forms a misleading reference line that drives continuous control inputs. Other illusions involve motion perception from surrounding scenery, or depth cues and object size giving misjudged distance, but they don’t describe the grass-generated horizon misperception that leads to persistent control inputs.