The only study I've ever seen on this has been based on simply grabbing the image off the reflection of the eye. I can't imagine this actually involved hooking up a cat's visual cortex to some sort of interface, the sheer processing power required for that sort of visual information processing is unfathomable.
If not, link me!
The retina has various layers and they took a look at what each layer does.
(It's less ridiculous than it sounds: Bananas contain a certain enzyme that helps to capture the neurons signals. The porridge they put around the sensors in the cats' brains contained many more things besides the bananas. My fiancee was studying that stuff in university.)
More here: http://www.stanley.bme.gatech.edu/research_topics_vision.htm...
As an analogy, imagine your eye lid twitches every time somebody mentions George Bush. The computer would then learn that when your eye lid twitches, you are thinking about George Bush. Not very exciting imo.
I think there was an experiment with a cat where they actually generated an image from what fell on the cat's retina. THAT was scary to me.