I'd imagine GP was referring to "humans perceive straight lines to be curved when certain shapes are overlayed", or "humans perceive shapes of the same color to

I'd imagine GP was referring to "humans perceive straight lines to be curved when certain shapes are overlayed", or "humans perceive shapes of the same color to be different colors when filters are applied" sorts of optical illusions. There are plenty of those, and I personally I think they're probably analogous to how adversarial filters fool AI classifiers.