Cognition in Aviation — Page 199, Lesson 314

I want to walk you through a new factor that affects how we perceive motion in the cockpit — something quite separate from the visual illusions we've been discussing. This is called the Kinaesthetic Effect. Let me define that precisely. The kinaesthetic effect gives you an illusion of climb with linear acceleration and an illusion of descent as a result of linear deceleration. So if your aircraft speeds up in a straight line, your body may trick you into thinking you're pitching up and climbing. If it slows down, you may feel as though you're descending. Now, what causes this? It's not coming from your eyes at all. It's caused by the resultant of the forces of gravity acting on the aircraft and the body. In other words, when you accelerate, the combined force vector from gravity and the acceleration tilts relative to your body. Your body senses that tilt and interprets it as a change in pitch attitude. These gravitational forces are picked up by the proprioceptors — that's a technical term for the sensory receptors located in your muscles and joints. They give you the sensation of climbing or descending, even when your aircraft is actually staying level. I want you to look at Figure 10.9 here on screen — it illustrates this relationship between the forces and the false sensation. Now, here's the critical point I need you to understand. The kinaesthetic effect is one thing, but the excerpt tells us that the result of these two quite different effects combine — the visual illusion we covered earlier and this kinaesthetic effect — under the right circumstances, they lead to an almost irresistible illusion of climb or descent. And this combination has led to many accidents over the years. That's not a theoretical concern; it's a documented causal factor in real mishaps. Figure 10.10 shows the somatogravic effect or illusion, which is the formal name for this combined phenomenon. Now let's move to protective measures against illusions. There's a common misconception that because visual illusions result from an unconscious process within the brain, there's nothing you can do about them. The excerpt tells us plainly: this is not true. Effective steps can be taken to substantially reduce the risks. The best protective measure is organized and formal training. It has been recommended that this training should educate flight crew to recognize five key things. First, that illusions are natural phenomena — they happen to everyone, and they're not a sign of weakness or poor skill. Second, the different types of illusions and their effects — you need to know what you're up against. Third, that the supplementation of other visual cues with information from other sources is the most effective counter to the effects of illusions. In plain language: don't rely only on what you see. Cross-check your instruments, your feel, your radio calls — bring in other sources of information. Fourth, the need for comprehensive flight briefing should the occurrence of illusions be known to exist or anticipated at particular geographic locations. If you're going into an airport where illusions are common — for example, a runway that slopes or sits near water — brief it thoroughly before you get there. Fifth, that special care must be taken by crew during accelerations and particularly when instrument flying. That's where the kinaesthetic effect and the combined illusions are most dangerous — when you're changing speed and when you're relying on instruments rather than a clear visual horizon. So the takeaway here is that illusions are real, they're powerful, and they combine in dangerous ways — but with proper training and cross-checking, you can protect yourself against them.