MOON lllUSION EXPLAINED

* Great, I said. Anu's subject entry font renders the capital I's and the small case l's the same. This is an excellent example of how the mind/eye translates reality into a trans-reality that has evolutionary function.
* Shoot, I said. When posted the I's and l's are differentiated. I guess I'll have to make all of them l's to make my point.
* Milum, wofahulicdoc said without really saying, you have misspelled the word "lllusion". You have spelled it "lllusian".
* Oh well, I said. Maybe that will trick people into overlooking the three l's.

Human Vision

*** The human eye/mind system can detect a change of only 2% within a brightness range of 1 to 100,000 candles per square meter. This acute distinction allows us to navigate a path by either sunlight or moonlight, a difference of a million in illuminance.

*** Each eye has a field of vision of over 100 degrees, and together our eyes are able to sense the presence of objects over an entire hemisphere, especially if they move. Although our field of view covers a wide angular area, there is a central region ,the fovea, which is more richly endowed with photoreceptors than any other part. When looking directly at an object, the feature of interest is directed to the fovea. Look at any word in this sentence. Focus on it. If you've focused you can't read its neighbor; now look at the semi-colon just made and try to scrutinize both parts simultaneously. It can't be done. The angle between them is only 0.3 degrees, and the remaining field of view falls of the retinal surroundings- the macula. We read by swift little stops and starts- one word at a time.

*** Each eye has a little blind spot at the connection to the optic nerve. We do not perceive this spot in our field of view. Instead the surrounding field fills it it, a process that is not fully understood. Thanks, probably to early learning, several other potential distractions are suppressed; that nose that protrudes into the scene; an image which is sharp only at the fovea and becomes indistinct at the periphery: and the eye's need for constant movement.

*** Find yourself a rainbow. Fixate on a part of the rainbow. Persist. Remember the eye naturally wanders. Suddenly you will become aware that the rainbow has vanished. Any motion of your eye will make it instantly reappear. The eye is a motion detector that requires constant movement to function. In truth if we could stop eye motion at will we could make any object fade away, the rainbow is just an easy subject because of its smoothness and lack of detail.

(be back in an eye blink)