Additional uncertainty arises from the fact that the brain must process and interpret the two-dimensional signals that are projected onto the retina, converting them into a representation of the actual three-dimensional world.
Humans get by with their imperfect eyesight pretty well, using knowledge of prior experiences and context from other senses to fill in the gaps, but there are times when it breaks down.
Among the earliest to document that fact was Aristotle, who found that if he stared at a moving stream for a while, then shifted his gaze to some rocks nearby, they appeared to move in the opposite direction. This phenomenon, now called motion aftereffect, occurs because the neurons that detect motion in a certain direction will adapt after being stimulated for a period of time, temporarily slowing their firing rate, Stocker said. That response results in the illusion of stationary objects moving in the reverse direction.
“It’s very clear that people don’t see the world the way it is in all kinds of ways,” Stocker said.
Another biological factor that can skew the vision of airborne personnel is fatigue — no surprise given that some long-range crews stay aloft more than 24 hours at a time, said Brian S. Pinkston, director of the aerospace medicine center at University of Texas Medical Branch in Galveston. Extreme fatigue can cause the brain’s visual cortex to register something that is not there, he said.
Equally potent is a phenomenon called autokinesis: the illusion that a stationary point of light is moving when it is viewed against a dark, featureless background.
“Your eyes have some inherent movement in them, and it will make it appear as if the object is moving,” said Pinkston, a former Air Force flight surgeon. “You can have stars in the sky, and it will appear as if they’re moving.”
Harder to explain are the occasions when similar sightings are experienced by multiple people, as in the case of Navy pilots interviewed by the New York Times. But there is some evidence that the culprit is advanced government technology of which the pilots were unaware, according to the Drive, a media outlet focusing on military affairs.
Whatever the true explanation, the key to analyzing new phenomena is a scientific principle called parsimony, said Scott Engle, an assistant professor of astrophysics and planetary science at Villanova University. In everyday English, parsimonious means being frugal with money. To a scientist, it means being frugal in making unwarranted assumptions.
“The explanation that requires the fewest assumptions or modifications to your understanding is usually going to be true,” said Engle, who studies the habitability of planets outside the solar system.
In the case of unexplained aerial sightings, that means — absent some extraordinary evidence — that the notion of alien spaceships simply does not hold water. There are so many questions. Among them: Wouldn’t we detect communication signals or some other sign of advanced beings before they traveled the vast distances needed to get here? And how would such a spacecraft even work?
Proxima b, a planet Engle has studied, is considered one of the nearest where conditions might be right for liquid water to exist on the surface. Yet it is 25 trillion miles away, a distance that would take thousands of years to travel with available technology. There is no reason to think some other life form has cracked the code of interplanetary travel.
“So they have the type of technology to visit us and are doing so in secret, but they accidentally slip up every once in a while and get spotted and then turn away?” Engle said. “Versus humans are imperfect and our eyes are imperfect and our optical processing is imperfect.”
No surprise: he goes for door No. 2.