> It's interesting that they were not able to extract good images from the test when they just asked the subjects to imagine the pictures. I speculate that is because the vast majority of people are able to recognize images of things, but not produce those images.

It seems reasonable to me. To use a computer as an analogy, the set of signals produced by a webcam recording a video to a hard drive are not going to be the same as the ones of the video playing from the hard drive on to the screen.