Coriolis Illusion

This involves the simultaneous stimulation of two semicircular canals and is associated with a sudden tilting (forward or backwards) of the pilot's head while the aircraft is turning. This can occur when you tilt your head down (to look at an approach chart or to write a note on your knee pad), or tilt it up (to look at an overhead instrument or switch) or tilt it sideways. This produces an almost unbearable sensation that the aircraft is rolling, pitching, and yawing all at the same time, which can be compared with the sensation of rolling down on a hillside. This illusion can make the pilot quickly become disoriented and lose control of the aircraft.

More spatial orientation illusions

The pilots' enjoyment of the spinning machines seems to come from surprises. "It's often connected to the unexpected," Bles says. Tilt the head while spinning with the eyes closed, for example, and suddenly, an intense tumbling sensation called the Coriolis illusion comes into play. "People find it fascinating," says Bles, "a very nice and unexpected sensation of movement." _Newsientist