Ooops sorry! It's being designed, no clinical experiment yet. I should reword my original comment.

http://www.polymtl.ca/polystim/en/navigation/Prothesevisuell...

There had been experiments showing that visual cortex stimulation to generate imagery is possible:

http://onlinelibrary.wiley.com/doi/10.1111/j.1528-1157.1998....