The point isn’t to rigorously define “visualize” or “imagine”—we will probably never be able to do this. The point is to use a verbal prompt to elicit a mental experience and then to try to probe that experience.

> A triangle doesn't have to be filled with a color to be a triangle. Why would you imagine it with any color in it in the first place, not just a wireframe, being transparent inside?

That’s just it: when I imagine a triangle, it is a definite image with a definite color. The visual details like color come automatically for me. I cannot imagine it in the more abstract way you are describing. If it’s a wireframe, the wireframe is gray. It’s always a full, colorful, 3d scene, perhaps vague but definitely with visual detail.