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11.7.9 Vision, Disorientation, Illusion

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Spatial Orientation

Changes occur as we grow from being a baby into early childhood. Gradually a baby learns about the forces that affect our orientation in the world. From that early age we begin to understand the force of gravity (G) and how it always acts vertically down. It is later in life that we learn that the force of gravity exerts a force of 1G, and that our visual horizon is horizontal with this force.

When pilots determine spatial orientation they use different senses:

  • The eyes
  • The vestibular system in the inner ear
  • The proprioreceptive sensors in the skin that confirm our position with the vestibular and vision senses - "seat of the pants"

To determine visual orientation other factors are taken into account, some of which are listed below:

  • The colour of an object.
  • The size and shape of the object.
  • The perspective.
  • Hue (shade) and parallax.
  • The groupings of objects.

Problems with spatial orientation begin with the eye - brain interface. "Seeing is believing" is often used, unfortunately, the eye does not always transmit enough information to the brain for us to interpret the truth. When dealing with Human Information Processing (HIP) we shall use the term 'perception". This part of the HIP process is built on past experience and expectation. So we can say in some instances that the eye is confused because perception has made its best attempt at telling us the truth.

The two pictures that follow show how easy it is to confuse the brain. The reversible goblet is a simple example of how perception is not a static process. You see a candelabrum or two faces looking at each other. The brain does not fix on one image, but constantly reminds you of each picture. In reality, you are unable to concentrate on one of the interpretations; both the candelabra and faces are continuously interpreted.

A more difficult interpretation is the Toulouse Lautrec picture shown below.

Within the picture is an old lady and a young lady. Once unlocked it is difficult to concentrate on just one of the depictions in the diagram.

In both pictures you have been given no depth clue. The next diagrams are included for interest and rely on you believing that the flat plane is in fact 3-dimensional.

The circles diagram uses the concept of relative size. The centre circles are the same size but the one on the right looks larger. The tuning fork is an impossible diagram if looked at closely.

The two line diagrams are viewed as perspective drawings and the central two lines are seen as curves. Both lines are straight and parallel.

Sight is the most powerful sense. However, in the diagrams above, you have been easily deceived into believing what is obviously false.

In the next pages we look at how this deficiency translates into the airborne environment.

Spatial Disorientation

Since the 1920's when the Royal Air Force designed the first blind flying panel the problems of instrument flying have been recognised. The standard "T" of instruments that you use in modern aircraft was in fact developed in 1927. By training and technological innovation, the number of accidents attributed to disorientation has fallen over the past few years. It must be remembered that if the power of vision is removed then the pilot will lose control of the aircraft.

The USAF demonstrated this by using a simple test. Three experienced pilots flew simple manoeuvres with their visual and instrument clues removed. The results in the diagram above show that in straight and level flight control could only be maintained for approximately 60 seconds.