Earlier quoted context omitted.
I was always slightly perplexed as to how that difference in orientation of colors leads to the out/in effect. I guess it's not so much the left/right but the top/bottom that really achieves this phenomenon, given how most daily light sources come from above (sun, ceiling fixtures, floor lamps) and there are relatively few instances of uplighting (landscaping, ...) around us.
The up–down orientation unquestionably comes from the near-universality of light sources being above you. You'll notice that intense up-lighting is almost never found in the natural or artificial world. (It's true that upwards-firing lights are often used in interior decoration, but these are almost always to illuminate walls and ceilings above us which then bounce light down to the contents of a room. Also, some tec…
I'm not sure the left/right shadows are a learned thing from user interfaces. As a kid, long before I got my first computer I was drawing 3D forms. Shadows always was drawn as light came from the upper left.
Maybe this is because I draw with right hand so prefer light to come from the left so I don't shadow my hand?