Cognition in Aviation 10

An Illusion of Movement

Move the page slowly away then towards the face while concentrating on the central dot.

Cognition in Aviation 10

Atmospheric Perspective

Visual illusions in flying are often associated with inappropriate experiences. For example the pilot who has done most of his flying in relatively polluted air may have learned to use ‘atmospheric perspective’ as a good cue to range. If the pilot then operates in a very clear atmosphere he/she may believe distant objects, because of their clarity, to be much closer than they actually are, or mistake the distant object for a similar, smaller, object he/she was expecting to see close by - both the expected and actual object will give the same angular size on the retina.

A number of accidents have occurred in the polar regions in VMC when the pilots have miscalculated the distance to a landing spot situated close to a landmark with the result that the aircraft has run out of fuel.

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Other Sources of Illusions

The GestaltTheory

Our senses - sight, hearing, touch etc. - do not account for all the sensory illusions. Sometimes the perception is correct, but comprehension and identification may be in question. The human brain is continually working on the construction of mental models. The Gestalt Theory (from the German word gestalt = shape) of learning proposes that any individual’s understanding of the world results from sorting out and combining multiple cues perceived in the environment until a ‘coherent whole’ appears that is acceptable according to the individual’s standards as regards the world.

Gestalt psychologists propose that perception, rather than being a simple repeated association between a stimulus and a response, is an active construction of an object by the brain.

Aviation in Cognition 10

Laws of Perceptual Organization

To reach this ‘coherent whole’ the brain has developed a set of rules about the combination of all the cues available. These rules are the laws of perceptual organization of the Gestalt Theory and deal with factors such as proximity, continuity, similarity, symmetry, simplicity and closure. In many cases an individual will add cues which are not in the environment, and which the brain thinks are hidden or not visible in what has been perceived.

Basically, Gestalt laws formulate basic principles governing how objects are organized and perceived.

As an example of the application of the Gestalt laws it is possible to make sense out of a number of words where half of the letters have been removed. The brain of the observer will ‘fill in’ the missing portions of the text to match what he believes is correct. The danger in this is that what the individual fills in will depend greatly on that individual’s previous experience and expectation.

Consider the following ...... P y ol g st. A psychology student would probably read it as - Psychologist whereas a biology student could read Physiologist.

One must use extreme caution to ensure that we do not construct our mental model according to our wishes or desires.

Illusions When Taxiing

Relative Movement

Even on the ground we are not free of illusions. A loading bridge moving away from the aircraft may give an illusion that it is the aircraft that is moving. When arriving at a gate which itself may be moving the pilot may believe that the aircraft is stationary and apply the parking brake, perhaps causing cabin staff to be thrown forward with the danger of injury.

Blowing snow may give a false impression of relative speed. When an aircraft is taxiing with a tailwind, the snow may appear to be falling vertically, giving the impression that the aircraft has stopped, when in fact it may still have a relatively fast taxiing speed. Application of the parking brake in these circumstances again could have serious consequences. Alternatively the aircraft could creep forward, colliding with an obstacle, when it was thought to be stationary. When taxiing into a headwind the blowing snow will give the illusion that the aircraft is taxiing faster than is the fact. In either case the pilot must look out of the side cockpit windows to gain an accurate assessment of taxi speed.

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Cognition in Aviation

Cockpit Height above the Ground

Pilot eye height from the ground may be the source of misjudged speed. Pilots converting to an aircraft with an eye position that is higher than on their previous type (8.66 m above the ground on a 747 compared with 3.48 m on a DC9) will have their normal visual references at a greater distance, which will give the illusion of slower relative motion, and in the initial stages of training they may well taxi at excessive speeds as a result.

Illusions on Take-off

Somatogravic Illusion

In commercial flying the major accelerations in the longitudinal and rotational planes occur on the take-off and go-around. An acceleration gives the pilot an impression of the nose of the aircraft pitching up and this encourages the pilot to push forward the stick with the resultant danger of flying into the ground.

The effect is due to the brain resolving the weight, acting vertically downwards, and acceleration into a single resultant force. The fact that this phenomena is exacerbated by the information supplied by the otoliths of the inner ear makes it particularly dangerous (Figure 10.9.)

Outside References

Outside references (vectional false horizons) may give false impressions within the cockpit.

Among these are:

•Immediately after take-off - a false horizon may be perceived when surface lights are confused with stars.

•Over water - the lights of fishing boats have been mistaken for stars and the flight path adjusted inappropriately.

•In hilly terrain - it is possible that, emerging from low cloud or mist on take-off, lights on the ground will be mistaken for stars and the flight path adjusted to a lower and dangerous profile.

•Gently sloping terrain - may create an illusion at any time when flying visually at low level.

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Cognition in Aviation 10

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10 Cognition in Aviation

PERCEIVED ATTITUDE

10 in Cognition Aviation

TRUE HORIZON

Figure 10.4 Example of vectional false horizon

•A bank of sloping cloud - across the horizon will give the impression of a wing low. (See

Figure 10.4 above.)

•After take-off or on approach - if the ground slopes down an illusion of excessive height may be created, and vice versa.

Illusions in the Cruise

Autokinesis

Staring at an isolated and stationary light when other visual references are inadequate or absent, may cause autokinetic movements of the eyes. This gives the illusion that the light is moving and can lead the pilot to believe that a single star is another aircraft. Numerous cases have been reported of mistaken identity of lights. These illusions can be avoided by shifting the gaze to eliminate staring. The illusion is created by small movements of the eye ignored by the brain and interpreted as motion of the object.

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