[tim333]

> when I think of the word "circle", images of circles and spheres show up in my head

There seems some evidence that this stuff is fairly central to human intelligence and the ability to visualize in 3d is kind of hard wired. Deciphering meaning is approximately "seeing what it means" which can correspond to visualizing it in your head. For example "the cat sat on the mat" is a bunch of symbols but someone or some machine can convert that to an image of a cat sitting on a mat then I guess they've understood it.