Researchers from ATR Computational Neuroscience Laboratories in Japan used a functional MRI machine on the brain to read the letters and symbols that the eyes of a subject were seeing.
From Pink Tentacle:
The scientists were able to reconstruct various images viewed by a person by analyzing changes in their cerebral blood flow. Using a functional magnetic resonance imaging (fMRI) machine, the researchers first mapped the blood flow changes that occurred in the cerebral visual cortex as subjects viewed various images held in front of their eyes. Subjects were shown 400 random 10 x 10 pixel black-and-white images for a period of 12 seconds each. While the fMRI machine monitored the changes in brain activity, a computer crunched the data and learned to associate the various changes in brain activity with the different image designs.
Then, when the test subjects were shown a completely new set of images, such as the letters N-E-U-R-O-N, the system was able to reconstruct and display what the test subjects were viewing based solely on their brain activity.