Originally posted by pauljs75
I guess these are like little blu-ish flashes that happen near ground and not necessarily in the sky? It's like a strobe almost. Flash there, then two feet over, etc. They can happen within tree-cover or even down in the grass.

Originally posted by pauljs75
If that's the case then I've seen that one or two times, maybe even indoors. Never had anyone else validate it in my case, so summed it up to sleep deprivation or a neuron misfiring.

Night Sight Skills

The ability to judge distances and heights at night is difficult at night. The absence of haze or its presence can cause illusions at night. Lights will vary in intensity and cause illusion effects. A misidentified light source can cause total confusion. A single light gives no altitude information. Multiple lights may be in different geometric visual planes. Freeways become visible while country roads disappear. Aircraft and lighted towers become visible for miles. Airports have beacons. The most common illusion is a narrow runway that appears to be longer than it is. the narrow runway may make you think that you are too high. Have a set procedure; allow an extra wide downwind at night. Know the length of your destination runway. Required FAR knowledge on all flights! All illusions are made worse at night.

Explanations of illusions must be taken with appropriate skepticism. Many are of the nature of "plausible hypotheses." Most are not (as yet) such that they can be independently verified in terms of physical processes in the brain. Also, we know that our visual perceptions arise because our brain synthesizes multiple cues. Our brain weighs these cues; some dominate in certain conditions, while others are "weaker" and are ignored. But the weightings shift in strength according to the nature of the stimuli. Many classic visual illusions arise from conflicting sensory cues of nearly equal "strength".

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When we judge the size of an object near the horizon our perception is influenced by familiar terrestrial objects in the field of view (trees, houses, roads). We know from everyday experience that many of the recognizable things we see in the distance are quite far away. But when our gaze is upwards, we have no reference cues for distance, and judge things near the zenith to be closer than those on the horizon.

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Perceptions are influenced by our past experience. One model of visual perception postulates that when we perceive a new and unfamiliar phenomenon our brain interprets it by comparing it to a mental map or model of our memory of previous sensory experiences. Of course, this represents just one of the cues that the brain must sort out, weighing it against other cues. Conflict between sensory cues is the basis of many common visual illusions.

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This is the same as saying, "What is our judgment of actual size of two things at different perceived distances, even though they have the same angular size?" The answer is that the one assumed nearer is judged to be smaller. This conclusion is consistent with the mental judgment that the horizon moon is farther from us.

This process supposedly operates even (especially) in the absence of any other visual cues. But the process is confused when we have our heads in an unusual position. This may be the result of our knowledge of the orientation of our head, from visual cues, and perhaps from information from the balance-sensing mechanisms of our inner ear. When there are competing sensory cues, our judgment of angular size can be altered by them, which may account for the confusing results of experiments designed to show that visual cues are the sole reason for the moon effect.

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The hard-wired hypothesis supposes that natural selection has shaped those brain mechanisms that process and interpret sensory data, devoting more resources to those things that are important to survival. This results in brain resources being biased toward things seen in front of us, fewer resources to things overhead. Similar imbalance of perception details are present in animals.

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How does this impression square with the situation in real (physical) space? The physical distance to the most distant object one can see on the horizon depends on the elevation of the observer's eye above the water. One can derive the formula for it, in terms of the earth's radius. For an eye elevation of six feet, the things we see on the horizon are actually about 3 miles away. Alto-cumulous clouds are about 2 to 3.5 miles overhead. So, physically, the distances are nearly the same, yet the overhead clouds seem much closer to most people than those near the horizon. This calculation may not seem quite fair, for we can see clouds that are physically well beyond the surface horizon, perhaps 10 miles away, due to their height above the earth surface. But can any reader and observer honestly claim that the clouds at the horizon seem farther away than the horizon? I've never found anyone who would make that claim.

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We have a strong impression that the cloud cover "joins" the horizon. Can this simply be that there's absolutely no visual cue to suggest that they are at different distances? Our brain may be making the simplest reconciliation of the situation.

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The moon illusion is consistent with what would be expected from evolutionary considerations. We have evolved cognitive processes that provide high quality visual information from nearby things, and things on our level that we can walk to and experience from various angles. These are all important to survival. Things seen high above, in the sky, or even those seen below, as when looking over the edge of a cliff, are less important. Therefore distance discrimination and detailed judgment of other visual properties of overhead objects is compromised.