I used to give a lecture every Wednesday over at the Hughes Aircraft Company, and one day I got there a little ahead of time, and was flirting around with the receptionist, as usual, when about half a dozen people came in - a man, a woman, and a few others. I had never seen them before. The man said, "Is this where Professor Feynman is giving some lectures?"

"This is the place," the receptionist replied.

The man asks if his group can come to the lectures.

"I don't think you'd like 'em much," I say. "They're kind of technical."

Pretty soon the woman, who was rather clever, figured it out: "I bet you're Professor Feynman!"

It turned out the man was John Lilly, who had earlier done some work with dolphins. He and his wife were doing some research into sense deprivation, and had built some tanks.

"Isn't it true that you're supposed to get hallucinations under those circumstances?" I asked, excitedly.

"That is true indeed."

I had always had this fascination with the images from dreams and other images that come to the mind that haven't got a direct sensory source, and how it works in the head, and I wanted to see hallucinations. I had once thought to take drugs, but I got kind of scared of that: I love to think, and I don't want to screw up the machine. But it seemed to me that just lying around in a sense-deprivation tank had no physiological danger, SO I was very anxious to try it.

I quickly accepted the Lillys' invitation to use the tanks, a very kind invitation on their part, and they came to listen to the lecture with their group.

So the following week I went to try the tanks. Mr. Lilly introduced me to the tanks as he must have done with other people. There were lots of bulbs, like neon lights, with different gases in them. He showed me the Periodic Table and made up a lot of mystic hokey-poke about different kinds of lights that have different kinds of influences. He told me how you get ready to go into the tank by looking at yourself in the mirror with your nose up against it - all kinds of wicky-wack things, all kinds of gorp. I didn't pay any attention to the gorp, but I did everything because I wanted to get into the tanks, and I also thought that perhaps such preparations might make it easier to have hallucinations. So I went through everything according to the way he said. The only thing that proved difficult was choosing what color light I wanted, especially as the tank was supposed to be dark inside.

A sense-deprivation tank is like a big bathtub, but with a cover that comes down. It's completely dark inside, and because the cover is thick, there's no sound. There's a little pump that pumps air in, but it turns out you don't need to worry about air because the volume of air is rather large, and you're only in there for two or three hours, and you don't really consume a lot of air when you breathe normally. Mr. Lilly said that the pumps were there to put people at ease, so I figured it's just psychological, and asked him to turn the pump off, because it made a little bit of noise.

The water in the tank has Epsom salts in it to make it denser than normal water, so you float in it rather easily. The temperature is kept at body temperature, or 94, or something - he had it all figured out. There wasn't supposed to be any light, any sound, any temperature sensation, no nothing! Once in a while you might drift over to the side and bump slightly, or because of condensation on the ceiling of the tank a drop of water might fall, but these slight disturbances were very rare.

I must have gone about a dozen times, each time spending about two and a half hours in the tank. The first time I didn't get any hallucinations, but after I had been in the tank, the Lillys introduced me to a man billed as a medical doctor, who told me about a drug called ketamine, which was used as an anesthetic. I've always been interested in questions related to what happens when you go to sleep, or what happens when you get conked out, so they showed me the papers that came with the medicine and gave me one tenth of the normal dose.

I got this strange kind of feeling which I've never been able to figure out whenever I tried to characterize what the effect was. For instance, the drug had quite an effect on my vision; I felt I couldn't see clearly. But when I'd look hard at something, it would be OK. It was sort of as if you didn't care to look at things; you're sloppily doing this and that, feeling kind of woozy, but as soon as you look, and concentrate, everything is, for a moment at least, all right. I took a book they had on organic chemistry and looked at a table full of complicated substances, and to my surprise was able to read them.

I did all kinds of other things, like moving my hands toward each other from a distance to see if my fingers would touch each other, and although I had a feeling of complete disorientation, a feeling of an inability to do practically anything, I never found a specific thing that I couldn't do.

As I said before, the first time in the tank I didn't get any hallucinations, and the second time I didn't get any hallucinations. But the Lillys were very interesting people; I enjoyed them very, very much. They often gave me lunch, and so on, and after a while we discussed things on a different level than the early stuff with the lights. I realized that other people had found the sense-deprivation tank somewhat frightening, but to me it was a pretty interesting invention. I wasn't afraid because I knew what it was: it was just a tank of Epsom salts.

The third time there was a man visiting - I met many interesting people there - who went by the name Baba Ram Das. He was a fella from Harvard who had gone to India and had written a popular book called Be Here Now. He related how his guru in India told him how to have an "out of-body experience" (words I had often seen written on the bulletin board): Concentrate on your breat h, on how it goes in and out of your nose as you breathe.

I figured I'd try anything to get a hallucination, and went into the tank. At some stage of the game I suddenly realized that - it's hard to explain-I'm an inch to one side. In other words, where my breath is going, in and out, in and out, is not centered: My ego is off to one side a little bit, by about an inch.

I thought: "Now where is the ego located? I know everybody thinks the seat of thinking is in the brain, but how do they know that?" I knew already from reading things that it wasn't so obvious to people before a lot of psychological studies were made. The Greeks thought the seat of thinking was in the liver, for instance. I wondered, "Is it possible that where the ego is located is learned by children looking at people putting their hand to their head when they say, 'Let me think'? Therefore the idea that the ego is located up there, behind the eyes, might be conventional!" I figured that if I could move my ego an inch to one side, I could move it further. This was the beginning of my hallucinations.

I tried and after a while I got my ego to go down through my neck into the middle of my chest. When a drop of water came down and hit me on the shoulder, I felt it "up there," above where "I" was. Every time a drop came I was startled a little bit, and my ego would jump back up through the neck to the usual place. Then I would have to work my way down again. At first it took a lot of work to go down each time, but gradually it got easier. I was able to get myself all the way down to the loins, to one side, but that was about as far as I could go for quite a while.

It was another time I was in the tank when I decided that if I could move myself to my loins, I should he able to get completely outside of my body. So I was able to "sit to one side." It's hard to explain - I'd move my hands and shake the water, and although I couldn't see them, I knew where they were. But unlike in real life, where the hands are to each side, part way down, they were both to one side! The feeling in my fingers and everything else was exactly the same as normal, only my ego was sitting outside, "observing" all this.

From then on I had hallucinations almost every time, and was able to move further and further outside of my body. It developed that when I would move my hands I would see them as sort of mechanical things that were going up and down - they weren't flesh; they were mechanical. But I was still able to feel everything. The feelings would be exactly consistent with the motion, but I also had this feeling of "he is that." "I" even got out of the room, ultimately, and wandered about, going some distance to locations where things happened that I had seen earlier another day.

I had many types of out -of-the-body experiences. One time, for example, I could "see" the back of my head, with my hands resting against it. When I moved my fingers, I saw them move, but between the fingers and the thumb I saw the blue sky. Of course that wasn't right; it was a hallucination. But the point is that as I moved my fingers, their movement was exactly consistent with the motion that I was imagining that I was seeing. The entire imagery would appear, and be consistent with what you feel and are doing, much like when you slowly wake up in the morning and are touching something (and you don't know what it is), and suddenly it becomes clear what it is. So the entire imagery would suddenly appear, except it's unusual, in the sense that you usually would imagine the ego to be located in front of the back of the head, but instead you have it behind the back of the head.

One of the things that perpetually bothered me, psychologically, while I was having a hallucination, was that I might have fallen asleep and would therefore be only dreaming. I had already had some experience with dreams, and I wanted a new experience. It was kind of dopey, because when you're having hallucinations, and things like that, you're not very sharp, so you do these dumb things that you set your mind to do, such as checking that you're not dreaming. So I perpetually was checking that I wasn't dreaming by - since my hands were often behind my head - rubbing my thumbs together, back and forth, feeling them. Of course I could have been dreaming that, but I wasn't: I knew it was real.

After the very beginning, when the excitement of having a hallucination made them "jump out," or stop happening, I was able to relax and have long hallucinations.

A week or two after, I was thinking a great deal about how the brain works compared to how a computing machine works - especially how information is stored. One of the interesting problems in this area is how memories are stored in the brain: You can get at them from so many directions compared to a machine - you don't have to come directly with the correct address to the memory. If I want to get at the word "rent," for example, I can be filling in a crossword puzzle, looking for a four-letter word that begins with r and ends in t; I can be thinking of types of income, or activities such as borrowing and lending; this in turn can lead to all sorts of other related memories or information. I was thinking about how to make an "imitating machine," which would learn language as a child does: you would talk to the machine. But I couldn't figure out how to store the stuff in an organized way so the machine could get it out for its own purposes.

When I went into the tank that week, and had my hallucination, I tried to think of very early memories. I kept saying to myself, "It's gotta be earlier; it's gotta be earlier" - I was never satisfied that the memories were early enough. When I got a very early memory - let's say from my home town of Far Rockaway - then immediately would come a whole sequence of memories, all from the town of Far Rockaway. If I then would think of something from another city - Cedarhurst, or something - then a whole lot of stuff that was associated with Cedarhurst would come. And so I realized that things are stored according to the location where you had the experience.

I felt pretty good about this discovery, and came out of the tank, had a shower, got dressed, and so forth, and started driving to Hughes Aircraft to give my weekly lecture. It was therefore about forty-five minutes after I came out of the tank that I suddenly realized for the first time that I hadn't the slightest idea of how memories are stored in the brain; all I had was a hallucination as to how memories are stored in the brain! What I had "discovered" had nothing to do with the way memories are stored in the brain; it had to do with the way I was playing games with myself.

In our numerous discussions about hallucinations on my earlier visits, I had been trying to explain to Lilly and others that the imagination that things are real does not represent true reality. If you see golden globes, or something, several times, and they talk to you during your hallucination and tell you they are another intelligence, it doesn'tmean they're another intelligence; it just means that you have had this particular hallucination. So here I had this tremendous feeling of discovering how memories are stored, and it's surprising that it took forty-five minutes before I realized the error that I had been trying to explain to everyone else.

One of the questions I thought about was whether hallucinations, like dreams, are influenced by what you already have in your mind - from other experiences during the day or before, or from things you are expecting to see. The reason, I believe, that I had an out-of-body experience was that we were discussing out-of-body experiences just before I went into the tank. And the reason I had a hallucination about how memories are stored in the brain was, I think, that I had been thinking about that problem all week.

I had considerable discussion with the various people there about the reality of experiences. They argued that something is considered real, in experimental science, if the experience can be reproduced. Thus when many people see golden globes that talk to them, time after time, the globes must be real. My claim was that in such situations there was a bit of discussion previous to going into the tank about the golden globes, so when the person hallucinating, with his mind already thinking about golden globes when he went into the tank, sees some approximation of the globes - maybe they're blue, or something - he thinks he's reproducing the experience. I felt that I could understand the difference between the type of agreement among people whose minds are set to agree, and the kind of agreement that you get in experimental work. It's rather amusing that it's so easy to tell the difference-but so hard to define it!

I believe there's nothing in hallucinations that has anything to do with anything external to the internal psychological state of the person who's got the hallucination. But there are nevertheless a lot of experiences by a lot of people who believe there's reality in hallucinations. The same general idea may account for a certain amount of success that interpreters of dreams have. For example, some psychoanalysts interpret dreams by talking about the meanings of various symbols. And then, it's not completely impossible that these symbols do appear in dreams that follow. So I think that, perhaps, the interpretation of hallucinations and dreams is a self-propagating process: you'll have a general, more or less, success at it, especially if you discuss it carefully ahead of time.

Ordinarily it would take me about fifteen minutes to get a hallucination going, but on a few occasions, when I smoked some marijuana beforehand, it came very quickly. But fifteen minutes was fast enough for me.

One thing that often happened was that as the hallucination was coming on, what you might describe as "garbage" would come: there were simply chaotic images - complete, random junk. I tried to remember some of the items of the junk in order to be able to characterize it again, but it was particularly difficult to remember. I think I was getting close to the kind of thing that happens when you begin to fall asleep: There are apparent logical connections, but when you try to remember what made you think of what you're thinking about, you can't remember. As a matter of fact, you soon forget what it is that you're trying to remember. I can only remember things like a white sign with a pimple on it, in Chicago, and then it disappears. That kind of stuff all the time.

Mr. Lilly had a number of different tanks, and we tried a number of different experiments. It didn't seem to make much difference as far as hallucinations were concerned, and I became convinced that the tank was unnecessary. Now that I saw what to do, I realized that all you have to do is sit quietly - why was it necessary that you had to have everything absolutely super duper?

So when I'd come home I'd turn out the lights and sit in the living room in a comfortable chair, and try and try - it never worked. I've never been able to have a hallucination outside of the tanks. Of course I would like to have done it at home, and I don't doubt that you could meditate and do it if you practice, but I didn't practice.