In Slater's virtual version, volunteers in an immersive virtual environment administered "shocks" to a virtual woman character. Half of the volunteers could see the woman character; the others interacted only with text. The context of the experiment was that the virtual woman was answering questions in a test. When she gave an incorrect answer, volunteers were told to give her shocks of increasing voltage as time went on. The virtual woman responded with cries of pain and protest.

Despite the fact that all volunteers knew that the subject of the experiment was not a real human being, they typically became more anxious as the experiment proceeded. Measures of stress, like heart rate and palm sweatiness, increased for many volunteers. About fifty percent of those who could see the woman character confided after the experiment that they thought about quitting, and several of them actually did. Volunteers who could not see the woman character were more likely to administer shocks of maximum voltage than those who could see her.

Why would people care about a virtual character in a clearly contrived experiment? It appears that the emotional brain of the human volunteers didn't quite get the message that this was only virtual reality.

Milgram's classic experiment was about obedience to authority - how volunteers tended to obey an authority figure despite the warnings of conscience. He wrote:

Stark authority was pitted against the [participants'] strongest moral imperatives against hurting others, and, with the [participants'] ears ringing with the screams of the victims, authority won more often than not. The extreme willingness of adults to go to almost any lengths on the command of an authority constitutes the chief finding of the study and the fact most urgently demanding explanation.

In Slater's study, the remarkable thing is that the virtual reality setup appears to provide an accurate assessment of the body's anxious reaction to a morally conflicted situation. According to Slater, it does this without violating the ethics of experimenters; Milgram's experiment resulted in a year-long delay in his application for membership to the American Psychological Association due to ethics questions. Other psychologists have contested this, saying that even when this experiment is performed in a virtual environment, it still has an ethically troubling effect on participants.

I'm curious about what this experiment says about the different uses of virtual violence in science fiction. In Star Trek: The Next Generation, there are long sequences that take place in the holodeck - a virtual reality environment. In at least one episode, Captain Picard "guns down" virtual figures without appearing anxious. However, all of the human characters are very solicitous of the "feelings" of Commander Data, an android robot, and are concerned when he is harmed.