The expanding torture scandal has left the American public horror-struck at how casually the Bush administration and its employees countenanced torture techniques like sleep deprivation, waterboarding and stress positions. However, another form of torture was not just used on detainees, but is being used on at least 25,000 Americans right now.

That's the number of people currently held in long-term solitary confinement in the United States, living for years in 80-square-foot concrete cubes lit by round-the-clock fluorescent light, with little or no human contact. The U.S. is alone among developed countries in using long-term solitary confinement on a regular basis.

Academic scientific analysis of solitary confinement is still in its early stages, but the results are obvious, and echo the experiences of Americans who've been held in solitary confinement by terrorists or as prisoners of war. Human beings evolved to be social creatures. Solitary confinement drives us mad.

Wired.com spoke with psychologist Craig Haney of the University of California, Santa Cruz, an expert on long-term solitary confinement. Asked if it's torture, Haney replied, "For some people, it is."

Wired.com: Everybody's talking now about waterboarding and sleep deprivation and stress positions, but I haven't seen solitary confinement mentioned much. Why is that?

Craig Haney: My interpretation is that the other techniques are generally regarded as more severe. But solitary confinement is in the background of all this. It's assumed to be part of the environment in which torture is occurring. And it is itself a painful, potentially harmful condition of confinement.

Wired.com: What have you seen in your own work?

Haney: First let me note that solitary confinement has historically been a part of torture protocols. It was well-documented in South Africa. It's been used to torture prisoners of war.

There are a couple reasons why solitary confinement is typically used. One is that it's a very painful experience. People experience isolation panic. They have a difficult time psychologically coping with the experience of being completely alone.

In addition, solitary confinement imposes conditions of social and perceptual stimulus deprivation. Often it's the deprivation of activity, the deprivation of cognitive stimulation, that some people find to be painful and frightening.

Some of them lose their grasp of their identity. Who we are, and how we function in the world around us, is very much nested in our relation to other people. Over a long period of time, solitary confinement undermines one's sense of self. It undermines your ability to register and regulate emotion. The appropriateness of what you're thinking and feeling is difficult to index, because we're so dependent on contact with others for that feedback. And for some people, it becomes a struggle to maintain sanity.

That leads to the other reason why solitary is so often a part of torture protocols. When people's sense of themselves is placed in jeopardy, they are more malleable and easily manipulated. In a certain sense, solitary confinement is thought to enhance the effectiveness of other torture techniques.

Wired.com: Is it fair to say that the science of sensory deprivation is "soft," but the results are hard?

Haney: Yes. Human beings are socially connected organisms. It's only when people are deprived of that connection that how much we depend on feedback from other people and contact becomes apparent. And all but the most resilient people begin to experience various forms of deterioration in the face of it. I'm not suggesting that everyone doesn't recover, but not all of them do.

Wired.com: Confusion and loss of self-identity sounds uncomfortable, but is it profoundly damaging?

Haney: It's certainly profoundly damaging if people lose hold of their own sanity. For some people, their sense of themselves changes so profoundly and so fundamentally that they are unable to regain it.

The other thing that happens more frequently, under even less long-term solitary confinement, is that people lose the ability to interact with others. They have to learn how to live in a world in which they're in complete isolation. Their ability to be comfortable during social interaction and maintain relationships is permanently impaired.

And for some people, the actual experience of isolation is so painful that it generates an anxiety or panic reaction. People lose their ability to control themselves. They become uncontrollably and sometimes permanently depressed in the face of this kind of treatment. Others become angry and unable to control those impulses.

You also find people who suffer cognitive impairments. Their ability to process information is undermined. And it's not clear if these skills can be brought back.

Wired.com: How many people in long-term solitary confinement are permanently damaged?

Haney: It's difficult to estimate precisely, because the long-term solitary conditions themselves vary, and not all people are created equal in terms of psychological resiliency.

There tends to be a kind of sloppiness when we talk about this. Some people will point to a particular study where it doesn't look like the effects were especially harmful, and conclude that there's no harm to be concerned about. But there are many other studies showing a higher risk.

I've heard word informally that a large percentage of prisoners in Guantanamo have experienced psychiatric problems. Was it all because they were isolated? No. They were subjected to a variety of other things as well.

Wired.com: Based on your own experience with U.S. citizens in long-term solitary confinement, would you be able to hazard a guess as to how many have sustained long-term damage?

Haney: I don't know. We don't have good data on follow-ups of people who come out of this environment. This is not something that's easy to study, and not something that prison systems are eager to have people look at.

But I can tell you that large numbers of them are in pain and are suffering while they're in solitary confinement. And there is certainly anecdotal evidence that some people have left solitary confinement deeply disturbed. I know such cases. I've seen them. These are instances of people going into solitary confinement with no pre-existing psychological problems, who are given a clean bill of health when they go in. When they come out they have psychiatric problems that are permanent or long-lasting.

Wired.com: Does America need to change how it thinks of long-term solitary confinement?

Haney: Yes. In the last 30 or 40 years in the United States, we've slipped into more long-term use of solitary confinement. In some cases it's a more complete form than was used before.

We have an overwhelmingly crowded prison system in which the mandate to rehabilitate and provide activities for prisoners was suspended at the same time as the prison system became overcrowded.

Not surprisingly, prison systems faced with this influx of prisoners, and lacking the rewards they once had to manage and control prisoner behavior, turned to the use of punishment. And one big punishment is the threat of long-term solitary confinement. They've used it without a lot of forethought to its consequences. That policy needs to be rethought.

The debate over long-term solitary confinement is always over how much harm it does, not over what positive effects it can have on people subjected to it. That's because the latter answer is obvious: none. It's an extraordinarily expensive, extraordinarily wrong-headed way of trying to manage prisoner populations.

Wired.com: Do you consider it legalized torture?

Haney: I don't think correctional administrators always put people in solitary confinement just to make them feel pain. But to the extent that's done, to the extent they know that people in these environments will feel that pain, then that creeps very close to the definition of what's understood internationally as torture.

I think our sloppiness, our carelessness about how this policy has been implemented, raises very severe ethical concerns about the humane treatment of prisoners by both U.S. standards and international standards.

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