Development of the Moon Illusion?
Everybody knows the moon illusion: The moon looks bigger when it's near the horizon than when it's high overhead, despite the fact that it subtends the same visual angle in each case. This is part of what makes certain famous Ansel Adams photographs look weird. The illusion disappears if you view the moon through a paper towel roll, blocking out visual information about the horizon.
Various explanations of the moon illusion have been offered; I take no stand on them, but merely offer the following observation.
I was driving with my four-year-old son, Davy, along a stretch of road beside some hills. The moon was full. Because of the hills, the visual horizon from our perspective was wavy. As we drove, the horizon would rise up closer to the moon, as a hill rose to greet it, as it were, then drop away from the moon when there was a gap in the hills. The moon was very striking that night and I'd already noticed it, but had said nothing to Davy.
From the back seat, Davy said, "The moon is getting bigger and smaller!" I said, "It is?" and looked toward the moon again. It seemed to stay a constant size to me.
Now, one might expect Davy's experience to be the normal one, since the moon was sometimes nearer, sometimes farther from the visual horizon from our perspective. Perhaps that is the original experience of children, but adults learn to compensate somehow?