In the ongoing furor over the prison abuse in Iraq, one oft-heard question is, how could an ordinary person subject another human being to such inhumane treatment? There have been a few scientific studies of such behavior and such studies, and their findings, are controversial.

When Craig Haney first saw the pictures of the prisoner abuse in Iraq, he was shocked, but not surprised. He had seen such abusive behavior before, in, of all places, a university experiment.

"My reaction was not, how could this happen? My reaction really was, how could it not happen? If all the safeguards that need to be in place in a prison environment were not in place in that prison, then those photographs, as horrible as they are and the behavior that they depict, were inevitable," he said.

In 1971, Mr. Haney, now a psychology professor at the University of California at Santa Cruz, was one of the lead researchers on what has come to be known as the Stanford Experiment. To gauge behavior between jailers and inmates, the researchers built a mock prison in the basement of the campus psychology building. Student volunteers were split into two groups, guards and prisoners, to study prison behavior. So quickly did the guards turn sadistic and abusive that the two-week experiment was halted after only six days.

The guards in the experiment hooded their prisoners and forced them to strip naked. The similarities between the experiment and what has emerged from the U.S.-run Abu Ghraib prison in Baghdad, says Mr. Haney, are remarkable.

"It was a direct flashback," said Mr, Haney. "If you put some of the photographs side by side with the photographs that we have from this 33-year-old study, they're shockingly similar."

How people descend into sadistic or abusive behavior when conferred with authority has fascinated researchers for years, especially after the brutality of the Nazis in World War II came to light.

In a 1961 experiment by Stanley Milgram at Yale University, unwitting subjects were ordered by a supposed doctor to keep administering increasingly powerful electric shocks to someone strapped to a chair. Believing that the fake shocks to be real and causing intense pain, more than 60 percent nevertheless complied with the phony doctor's orders to ratchet up the shocks.

Mr. Haney says the experiments show up some unpleasant truths about how abominably people behave under the right conditions.

"Here's the hard thing to come to terms with: it is that bad and even sometimes what appears to be evil behavior does not require a bad or necessarily evil person to be produced," he said.

Mike Ritz, a former Army interrogator, says a psychiatrist should be present at a facility like Abu Ghraib precisely to prevent guards from losing their moral compass.

"If you go to the U.S. Army SERE school, the survival, resistance, escape training, there's a psychiatrist on board," he said. "And he's not just there for the people undergoing the experience as prisoners. He's also there to keep everyone else in check to make that they're not getting overwhelmed by this pseudo-god complex that happens to occur when you're in charge of people and you have a lot of power and authority."

Mr. Haney adds that abusive behavior is likely to increase in a combat environment, where the enemy is dehumanized and demonized to get soldiers to fight better.