From the dingy dungeons of the Dark Ages to today's shadowy holding facilities, the use of torture as an interrogation tactic has evolved little and possibly yielded even less, in terms of intelligence.

Inflicting pain to get information is a practice with deep roots as well as modern relevance, in light of the recent statements by President George W. Bush claiming the U.S. government does not use torture on political prisoners, despite some evidence to the contrary.

But aside from the moral and legal implications, does torture ever produce reliable intelligence?

"That's the impossible question," said Darius Rejali, a political scientist at Reed College in Oregon.

As a rule, torture is not an effective method of extracting information from prisoners, most experts agree.

"If anything useful came out these interrogations in Iraq, we would have heard about it," said Alfred McCoy, a University of Wisconsin-Madison historian and author of "A Question of Torture: CIA Interrogation, From the Cold War to the War on Terror" (Holt Paperbacks, 2006).

A history of violence

The question of torture has become more controversial of late due to a report in The New York Times on memos issued by the U.S. Justice Department in 2005, effectively authorizing intelligence agencies to use interrogation methods defined as torture under international law.

Psychological techniques such as the water-boarding and sleep deprivation that American operatives are suspected of using recently have a history going back to behavior experiments from the 1950s, McCoy said.

"They were looking for a key to unlock the mind," McCoy said of the CIA-funded research, "and the real breakthrough was that sensory deprivation could produce a mental disorientation akin to psychosis."

A switch from more physical methods of torture to the psychological approaches emerged in the following decades in places such as Vietnam, Central America and Iran, McCoy said, without any definitive proof of their effectiveness. When the "War on Terror" was initiated after the Sept. 11 attacks on the United States, the CIA had another training ground for this kind of interrogation at its Guantanamo Bay detention center.

"Guantanamo Bay turned into a de-facto behavioral science laboratory," McCoy told LiveScience, where sensory deprivation and self-inflicted pain—allowing a detainee who had stood for hours to sit if he would only "cooperate"—regularly took place.

Though captives are less resentful when tortured psychologically, it doesn't make their statements any more trustworthy, Rejali said.

"Torture during interrogations rarely yields better information than traditional human intelligence, partly because no one has figured out a precise, reliable way to break human beings or any adequate method to evaluate whether what prisoners say when they do talk is true," Rejali wrote in a 2004 article on Salon.com.

Torture 'light' still unreliable

There's no such thing as "a little bit of torture," McCoy said of the "light" tactics that are preferred today. Detainees are just as likely to tell their interrogators whatever they want to hear under psychological distress as they are under physical distress, he said, a statement backed up by Sen. John McCain, who himself was tortured as an officer during the Vietnam War.

Democracies, rather than dictatorships or oppressive regimes, are more likely to engage in this seemingly stealthy kind of torture because it is easier to hide from journalists and citizens, Rejali said.

"Torture is a sign that a government either does not enjoy the trust of the people it governs or cannot recruit informers for a surveillance system. In both cases, torture to obtain information is a sign of institutional decay and desperation," wrote Rejali, "and torture accelerates this process, destroying the bonds of loyalty, respect and trust that keep information flowing. As any remaining sources of intelligence dry up, governments have to torture even more."

Psychological torture has persisted in theaters such as the Iraq War not because it necessarily works, but because the CIA has such an institutional history of the practice, McCoy said.

"The interrogators themselves tend to believe in its efficacy, and no matter what you do, you can't stop them once they start," he said, noting that the false sense of power one gets from inflicting torture only fuels more advanced brutality.

Medieval torture more organized

The Medieval or Dark Ages are widely held up as the standard-bearer in brutal and organized torture. Famous dreaded devices such as the rack, the spiked Iron Maiden coffin and a very unpleasant, pyramid-shaped seat called the Judas Cradle were used to coerce victims into providing some desired information, often a false confession.

Despite the seemingly barbaric nature of Medieval torture, however, the methods used were actually part of an organized system of justice, as opposed to the clandestine nature of the interrogations allegedly being conducted by the CIA, Rejali said.

Medieval torture was neither sadistic nor savage compared to modern torture and was no more or less rational or driven by urgent security concerns, Rejali said.

"The only reason the question [of urgency] appears more interesting for us is because morally those are the only ways democratic societies are able to justify it to themselves," he said, adding that "the search for heretics was always a serious one, just as the search for terrorists is today."