Limits on human perception, and how they influence UFO sighting reports

To: Common Errors UFO Witnesses Make

Human Vision:

The human visual system is primarily adapted to simple close-up work. It fails miserably when someone tries to do any of the following tasks:

Many cases are unsolved because the investigator puts too much stock in the size, the distance, the speed, or the altitude reported by witnesses. When these are discounted as being the very inaccurate values they are, many times the solution is immediately apparent.

Human Hearing

Our hearing works well under ordinary circumstances, but is taxed under unusual circumstances. Here are some of the effects that are infrequently encountered:

Human Sense of Smell

The human sense of smell is very weak compared to that of other animals. It is nondirectional, and in most cases, detects whatever the wind brings in. Here are some common misperceptions:

Other Human Senses

The other human senses also can cause either misperceptions or special effects. Here are a few common effects:

Case Study

On February 2, 1993, people reported a UFO over Jefferson County, Kentucky. The police dispatched a helicopter to investigate. The following effects were reported by the helicopter crew:

  1. The object looked like a huge ball of fire.
  2. The object was larger than the helicopter.
  3. The object made "ramming attacks" at the helicopter as it tried to get close enough to identify it.
  4. The object changed brightness erratically.

People watching from the ground reported a different scenario:

  1. The object and the helicopter appeared as lights only.
  2. The object was smaller than the helicopter.
  3. The helicopter repeatedly went past the object. One witness reported that the helicopter didn't seem to be able to find the UFO, since it kept going right past it.
  4. The object changed brightness erratically.

The report of this incident in the paper the next day caused a man to come forward, saying that he had launched the object the previous night. It was a fire balloon made of a plastic dry cleaner bag, with a structure made of soda straws at the bottom that held some candles. He had launched it to observe wind direction at various altitudes, and had no idea that his balloon would cause so much trouble.

So how did a small fire balloon cause the effects the helicopter crew witnessed?

This shows that even highly trained people can make huge errors in judgment of the size of an object in the absence of other clues to its true location. Those policemen were not at fault in any way. Everyone has the same limitations. Nobody can accurately judge the size, distance, speed, or altitude of an unknown object without additional information. No amount of training can alter this fact.

So the next time a UFO witness gives numeric values for the size, distance, speed, or altitude of an unidentified flying object, the next question to ask is: "How do you know that value?"



Common Errors UFO Witnesses Make

Here is a list of the common errors UFO witnesses (and investigators) make when trying to perceive or report a UFO correctly:


  1. Assuming a "reasonable" size or distance when vision can't determine the actual value.
  2. Assuming that lens accommodation or eyeball convergence can work farther away than 30 feet.
  3. Assuming that parallax can work against a uniform background.
  4. Assuming that parallax works when the reference object is not in the central vision field at the same time.
  5. Placing the UFO at the same distance as a nearby landmark.
  6. Assuming that the sky is a plane surface, and attempting to measure distance with that surface through perspective or parallax.
  7. Overestimating angular size due to use of the sky as a perspective surface.
  8. Confusing scattering effects with the true color of the object.
  9. Discounting the effects of halation when determining whether an object crossed in front of or behind something.
  10. Assuming that an angular size estimate, a true size estimate, a distance estimate, a speed estimate, an angular velocity estimate, and/or an altitude estimate must all fit together for the same object at the same distance. Humans make inaccurate estimates.
  11. Reporting an angular size or a shape seen as a result of halation.
  12. Assuming that the UFO is the only light source casting shadows.
  13. Guessing that a UFO has one particular identity, and assuming a size, distance, speed, and/or altitude based upon this guess.
  14. Assuming that a UFO is a vehicle.
  15. Thinking that a man must be able to fit in the UFO.
  16. Assuming that great power is necessary to perform the observed motions.
  17. Once the true position is found by other means, scaling the size or speed reported to attempt to get the true values.
  18. Assuming intelligence is behind random motions.
  19. Not checking the visual capabilities of the witness.
  20. Expecting perfect vision (or perfectly corrected vision).
  21. Assuming the witness can measure angles without instruments.
  22. Overestimating the angular size of the UFO later, due to intense concentration on the object during the sighting.
  23. Assuming that a reconstruction of angular size is accurate.
  24. Assuming that the witness has accurately reported visually observed sizes, angular sizes, lengths, complex shapes, angles, light intensity, and colors.
  25. Discounting the effects of dark-adaptation.
  26. Overestimation of brilliance by overestimation of size and distance.
  27. Forgetting that color perception at night is very different.
  28. Assuming that colors reported at night are as saturated as they appear.
  29. Forgetting that background affects color perception.
  30. Ignoring the effects of optical illusions.
  31. Confusing whether an object is expanding, brightening, or approaching.
  32. Confusing whether an object is contracting, dimming, or receding.
  33. Assuming that an object moving away from the horizon is approaching or contracting, and that an object moving toward the horizon is receding or expanding.
  34. Putting too much faith in sizes, distances, speeds, or altitudes reported by witnesses.
  35. Expecting a witness to locate the sources of very low frequency or very high frequency sounds.
  36. Expecting a witness to locate the sources of sounds with an accuracy similar to that of vision.
  37. Assuming that the sound heard must have been produced by the UFO.
  38. Discounting reflections of sound.
  39. Assuming that any strange sound must have been produced by a UFO.
  40. Preconceiving how things are, and using those preconceptions in a UFO encounter.
  41. Deciding that a smell must have come from the UFO.
  42. Assuming that prickly or tingling sensations, temperature changes, lack of balance, sweating, spasms, or faintness must have been caused by a UFO.
  43. Thinking that the UFO must be a space ship.
  44. Assuming that the UFO is reacting to witness presence or actions.
  45. Thinking that a feeling of "being watched" means something. Strange situations cause that feeling.
  46. Assuming that animals are reacting to the presence of a UFO.
  47. Expecting strange effects because a UFO is sighted.
  48. Assuming that any equipment failure or anomaly must have been caused by the UFO, because of its presence.
  49. Believing that a UFO caused a power failure, instead of the more likely case that the power failure caused the UFO?
  50. Assuming that none of the perceived motions of the UFO are caused by witness motion.
  51. Disbelieving the true solution when it is found.

Specific Errors in UFO Cases:

  1. Mistaking an airplane reflecting sunlight specularly and halating as a "giant cloud cigar" or a missile.
  2. Mistaking an advertizing plane (with traveling light-up letters) seen edge-on for a rotating disk with portholes.
  3. Mistaking a small fire balloon close to the witness for a large UFO much farther away.
  4. Mistaking a meteor or re-entry that has broken into several parts for an "airship" with lighted portholes.
  5. Mistaking a series of parachute flares as a single giant UFO with lights.
  6. Mistaking a gliding bird for a domed disk seen edge-on.
  7. Mistaking a kite for an erratically moving UFO.
  8. Mistaking a wind-turbine kite for a rotating or flashing UFO.
  9. Mistaking a bright planet or star for a much closer UFO, especially if it is scintillating.
  10. Mistaking an electrical arc or an exploding transformer for a UFO that caused a power failure.
  11. Mistaking a small, stationary object for a larger object, farther away, that is moving in the opposite direction to your motion.
  12. Mistaking a photographic frame where a flashbulb failed to go off for another photo on the same roll of film that was taken of something too faint or distant to get on film.

Answer: The angular size of the rising full moon is about the size of a pea at arm's length. If you don't believe me, try it!

Answer: The angular size of the full moon directly overhead is also about the size of a pea at arm's length. Try this too!