While researching to answer Why are "Inverted Colors" considered an accessibility feature? I noticed the puzzling claim that "White text on a black background is a higher contrast to the opposite, so the letterforms need to be wider apart, lighter in weight and have more space between the lines." It's repeated a lot, particularly by design folks, but I couldn't find psychological research to support (or refute) it.
In terms of actual contrast ratio, inverting a black on white scheme won't change the contrast at all; the colors themselves are just as distant. Yet I see many claims that "inverted colors" is high contrast. The only real difference between the two I can think of is that the white background of black on white produces considerably more light than a black background. If this difference is enough to induce some level of ocular adaptation perhaps that could be a cause.
So is there a perceived difference in contrast between black on white vs white on black, assuming the same intensities for black/white? What causes it?