We Make Money Not Art has an interesting article about an updated Milgram Obedience experiment with a virtual shock recipient (the emphasis is theirs)
Participants who could see and hear the avatar were affected by the experiment as if it were real. Their stress responses were raised (as judged by sweating and heart rate). And when the woman protested, the participants tended to give her longer to answer before administering the shock. Some participants emphasised the correct answer among the available choices, as if trying to help the woman avoid a shock.
As Yishay Mor notes, the results put in a new light the idea that we should give human rights to sentient machines.