Aeromedical: Illusions

Question 1

Visual Illusions. (IMC, Day, Night, Tactical flt)

Answer 1

Illusions give false impressions or misconceptions of actual conditions; therefore aircrew members must understand the type of illusions that can occur & the resulting disorientation.

Although the visual system is the most reliable of the senses, some illusions can result from misinterpreting what is seen; what is perceived is not always accurate.

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Question 2

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Answer 2

False Horizon.

• Confusing cloud formations or uneven ground w/ the horizon.
• This is usually occurs when the aviator looks up after a prolonged period in the cockpit or from poor scanning technique.

Question 3

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Answer 3

Flicker Vertigo.

• A light flickering at a rate of 4 to 20 cycles per second can produce nausea, vomiting & vertigo.
• It can be caused by sunlight flickering through the rotor blades or by an anticollision light reflecting against an overcast sky at night.
• DO NOT CLOSE your eyes, it will intensify the effect.

Question 4

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Answer 4

Fixation.

• This occurs when aviators ignore orientation cues & fix their attention on a single goal or object without seeing the whole environment.
• May occur during times of task saturation or target fixation.

Question 5

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Answer 5

Confusion.

A common occurrence is to confuse ground lights with stars.

A good cross check will prevent this illusion

Question 6

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Answer 6

Relative Motion.

• Mistaking the motion of another aircraft or object for that of your own.
• Could occur during formation flight, hover taxi, or hovering over water or tall grass.
• The use of proper scanning techniques helps prevent this illusion.

Question 7

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Answer 7

Autokinesis.

• When a static light is stared at in the dark for 6 to 12 seconds, the light appears to move up too 20 degrees in any direction.
• Reduce or eliminate by visual scanning, increasing the number of lights, or by varying light intensity.

Question 8

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Answer 8

Structural illusion.

• The distortion of objects caused by heat waves, rain, snow or other factors that obscure vision.
• This illusion can be linked to mirages.

Question 9

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Answer 9

Height Perception Illusion.

• When flying over terrain lacking good contrast (water, desert, snow), crew members may think the aircraft is higher or lower than it actually is.
• This is due to a lack of visual references. It can be overcome by dropping an object of known size or intensity from the aircraft or by using shadows cast by surrounding objects or the aircraft.
• At night drop a chemstick or flare before landing.

Question 10

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Answer 10

Size-Distance Illusion.

• Viewing a source of light that is increasing or decreasing in luminance. The aviator may incorrectly interpret the light as approaching or retreating.
• It also is the false perception of distance from an object or the ground.
• It occurs when visual cues such as a runway or trees are different size than expected.
• Shooting an approach to a large runway vs. a small stage field lane. On larger runways an aviator may perceive he is too low when landing.

Question 11

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Answer 11

Altered Planes of Reference

• The pilot has an inaccurate sense of altitude, attitude, or flight path position in relation to an object so great in size that the object becomes the new plane reference.
• When approaching a line of mountains or clouds, aviators may feel they need to climb even though their attitude is adequate.

Question 12

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Answer 12

Reversible Perspective.

• At night, an aircraft may appear to be going away when it is actually approaching.
• This illusion often occurs when an aircraft is flying a parallel course.
• To avoid this illusion observe the lights. Red on right returning.

Question 13

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Answer 13

Crater Illusion.

• Occurs when aircrew members land at night, under NVG conditions, and the IR searchlight is directed too far under the nose of the aircraft.
• This will cause the illusion of landing with up-sloping terrain in any directions.
• Depressing lulls the pilot into continuing to lower the collective. Could result in the aircraft prematurely impacting the ground, causing damage.
• If observing another aircraft during hover taxi, the aviator may perceive that the crater actually appears to move with the aircraft being observed.