The Door to December

was barely illuminated by the meager light that found its way through the hatch; the sound of water stirred by the vibrations transmitted through the steps and into the tank frame; a dampish odor with a hint of salt to it.
     'Know what it is?' he asked.
     She descended the three steps. 'Sure. A sensory-deprivation chamber.'
     'What was he doing with it?'
     'You mean, what are its scientific applications?'
     Dan nodded.
     'Well, you fill it with a few feet of water.... Actually, you use a solution of ten percent magnesium sulfate in water for maximum buoyancy. Heat it to ninety-three degrees Fahrenheit, the temperature at which a floating body is least affected by gravity. Or depending on the nature of the experiment, maybe you heat it to ninety-eight degrees to reduce the differential between body temperature and water temperature. Then the subject—'
     'Which is a person — not an animal?'
     She looked surprised by the question. Dan Haldane felt woefully undereducated, but Laura didn't disparage him or let any impatience creep into her tone, and he felt at ease again almost immediately.
     She said, 'Yes. A person. Not an animal. Anyway, when the water's ready, the subject undresses, enters the chamber, closes the door after himself, and floats in total darkness, in total silence.
     'Why?'
     'To deprive himself of all sensory stimulation. No sight. No sound. Little or no taste. Minimal olfactory stimulation. No sense of weight or place or time.'
     'But why would anyone want to do that?'
     'Well, initially, when the first tanks were used, they did it because they wanted to find out what would happen when someone was deprived of nearly all external stimuli.'
     'Yeah? And what happened?'
     'Not what they expected. No claustrophobia. No paranoia. A brief moment of fear, yes, but then ... a not unpleasant temporal and spatial disorientation. The sense of confinement disappeared in a minute or so. Some subjects reported being certain they were not in a small chamber but a huge one, with endless space around them. With no external stimuli to occupy it, the mind turns inward to explore a whole new world of internal stimuli.'
     'Hallucinations?'
     For a moment, her anxiety faded. Her professional interest in the functioning of the human mind became evident, and Dan could see that, if she had chosen a career in the classroom, she would have proven a natural-born teacher. She clearly took pleasure in explaining, illuminating.
     She said, 'Yes, hallucinations, sometimes. But not frightening or threatening hallucinations, nothing like what you'd expect from a drug experience. Intense and extraordinarily vivid sexual fantasies in many cases. And virtually every subject reports a sharpening and clearing of thought processes. Some subjects have solved complex problems in algebra and calculus without even the benefit of paper and pencil, problems that would ordinarily be beyond their abilities. There's even a cult system of psychotherapy that uses deprivation chambers to encourage the patient to concentrate on guided self-exploration.'
     He said, 'From your tone, I think maybe you don't approve of that.'
     'Well, I don't exactly disapprove,' she said. 'But if you've got a psychologically disturbed individual who already feels adrift, only half in control of himself ... the disorientation of a deprivation chamber is almost certain to have negative effects. Some patients need every grip on the physical world, every external stimulus, they can get.' She shrugged. 'But then again, maybe I'm too cautious, old-fashioned. After all, they've been selling these things for use in private homes, must've sold a few thousand over the past few years, and surely a few of those were used by unstable people, yet I haven't heard of anyone going all the way 'round the bend because of it.'
     'Must be expensive.'
     'A tank? Sure is. Most units in private homes are ... new toys for the rich, I guess.'
     'Why would anyone buy one for his home?'
     'Aside from the hallucinatory period and the eventual clarity of the mental processes, everyone reports being tremendously relaxed and revitalized by a session in a tank. After you spend an hour floating, your brain waves match those of a Zen monk in deep meditation. Call it a lazy man's way to meditate: no studying