Vee haff vehs to mehk you tok.

Atrios posted on this NYT article here and here. And, others are posting on the article as well. Let's take a look at circadian / sleep part of this article.

American guards arrived at the man’s cell periodically over the next several days, shackled his hands and feet, blindfolded him and took him to a padded room for interrogation, the detainee said. After an hour or two, he was returned to his cell, fatigued but unable to sleep.

The fluorescent lights in his cell were never turned off, he said. At most hours, heavy metal or country music blared in the corridor. He said he was rousted at random times without explanation and made to stand in his cell. Even lying down, he said, he was kept from covering his face to block out the light, noise and cold. And when he was released after 97 days he was exhausted, depressed and scared. ...

Bread and powdered drink for breakfast and sometimes a piece of fruit. Rice and chicken for lunch and dinner. Their cells had no sinks. The showers were irregular. They got 60 minutes in the recreation yard at night, without other detainees.

Five times in the first week, guards shackled the prisoners’ hands and feet, covered their eyes, placed towels over their heads and put them in wheelchairs to be pushed to a room with a carpeted ceiling and walls. There they were questioned by an array of officials who, they said they were told, represented the F.B.I., the C.I.A., the Naval Criminal Investigative Service and the Defense Intelligence Agency.

“It’s like boom, boom, boom,” Mr. Ertel said. “They are drilling you. ‘We know you did this, you are part of this gun smuggling thing.’ And I’m saying you have it absolutely way off.”

The two men slept in their 9-by-9-foot cells on concrete slabs, with worn three-inch foam mats. With the fluorescent lights on and the temperature in the 50s, Mr. Vance said, “I paced myself to sleep, walking until I couldn’t anymore. I broke the straps on two pair of flip-flops.”

Cognitive performance--which'd play a role when someone is trying to keep information secret--is influenced in part by both subjective "sleepiness" as well as a marked circadian rhythm of cognitive ability. A "circadian" rhythm is an endogenous rhythm we all express that is approximately 24 hours in length and controls various physiological functions such as body temperature rhythms, etc. Cognitive performace peaks when body temperature peaks. Cognitive performance--as we can probably all atest to--is lowest when we feel the greatest need for sleep. Hence, if you want to get somene to slip his cover and possibly reveal things he/she would not otherwise reveal, you would want to ask questions at both the circadian nadir of cognitive performance as well as a time at which the prisoner [in this case] is feeling subjectively tired.

Actual sleep deprivation (awakening the prisoner while he/she is falling asleep using whatever works) will probably get you in trouble with the Geneva Conventions or some other such guiding principle of prisoner treatment. So what to do? Well, you could either try to desynchronize the circadian rhythm (of body temperature and other physiological functions) with bouts of sleep and wakefulness or attempt to obliterate entirely the prisoner's circadian rhythm. How?

Exactly as is done here. First, you want the prisoner to not receive any actual time-of-day information. That's what the constant light, constant low temperature and random awakenings will do. Moreover, the prisoner's right to outdoor activity was restricted to the night, where it's much more difficult to figure out whether it's early or late night. And food administration was repetitive enough that it wasn't associated with time inputs: either fruit or chicken was given relative to when the prisoner woke up, not the actual time of day. What happens after about two weeks of this sort of disorienting treatment is that the prisoner's internal clock begins to become desynchronized from the rest of the world. This is because the timekeeping mechanism in mammals is not perfect, and runs slightly longer than 24 hours in humans so that in the absence of other stimuli, we're going to have longer days than we otherwise would if we knew what time it was. Add to that random awakenings and the prisoner will begin to catch sleep whenever possible and whenever the circadian drive for wakefulness isn't completely opposed to sleep drive. So you could possibly have the prisoner willingly awake during a time when his cognitive functions are lowest. But in the end, what you really want during interrogations is presumably not a robust circadian rhythm that's simply desynchronized with the outside world and the prisoner's sleep-wake bouts, you want to completely obliterate the circadian rhythm and have a constant low cognitive performance.

That's basically what the constant bright lights will do. Most human "forced desynchrony" protocols in research labs involve constant dim lighting conditions to throw the circadian clock and the individual's desire for sleep out of synchronization. Here, bright lights--regarless of how dim you think fluorescent lights are compared to ambient outdoor lighting, they're brighter than dim lights--were used. After about 10 days or so of bright lights, most rodents become almost completely "arhythmic" meaning their 24 hour rest-active cycle is completely gone and they randomly either sleep or run their wheels or eat, groom, whatever. I don't think there's much information on how humans behave under these circumstances but I'd suspect it'd be similar. Constant bright lights will cause you to pick times to sleep whenever it's possible, rather than whenever you should be sleeping. And, constant bright lights and loud music will cause you to be generally sleep-deprived for obvious reasons. It's hell.

Though the prisoner was never actually sleep-deprived in the sense that he wasn't physically roused while falling asleep, the effect is essentially the same. After 97 days of this, anyone would feel exhausted. Also, long-term sleep deprivation would lead to symptoms of depression and there's a good literature out there on that; but I suppose he might have major depression for other reasons as well!

So, was this part of his incarceration legal? There wasn't any actual sleep deprivation, just discomfort leading to lack of sleep.