> I've got a question for you:
> Normally my blank screen is a chaotic soup of bright and dark micro-
> molecules, too small and too changing to single out and hold any one  
> particle  (unlike your experience of moving inside a single  
> particle).  But by the end of every retreat, I have spontaneous  
> occurrences of a solid gray field, absolutely unwavering and  
> unchanging -- and it's incredibly blissful and peaceful.  Is that a  
> kasina?  I think it probably is, and that it's normally inaccessible  
> because my daily intake of computer and tv stimulation results in too  
> much excitation.  So, is there any way to induce that kasina at will,  
> or do I just have to wait for it to occur naturally in a sensory-
> deprived environment?

I would say, yes, it's probablya kasina.  (Although I am hardly an expert on that particular subject and, of course, encourage you to ask Shinzen or Leigh or someone who knows more about it than I do.

From what little I know of kasinas (from Shinzen, Leigh & minimal reading), I know that I have not experienced them all - nor have I attempted or particularly wished to - so that should factor in to how you receive my response.)

And I've got to give another disclaimer to what I'll say because as soon as you deal with jhanas or kasinas or any other experience in meditation, there's just the element of 'grace' vs. 'effort' that is hard to predict/explain... (i.e. I’m going to tell you actions or habits that may help, may not, and/or it could just happen spontaneously without any effort at all.)

My personal take is that my 'moving inside a single particle', as you put it, is my habit of cultivating that from having had a significant experience many years ago and attempting (often successfully - for better or worse) to re-create it.  So there's a 'Feel', i.e. an emotion, that helps motivate me to 'lock on' my awareness to that particular 'particle' of my experience.  

Is it easier in a sensory-deprived environment?  Of course.  But my experience has been that when I get (say, at the end of a retreat) to a place where I can easily drop down, my mind isn't so stimulated, etc, it's the transition back into the world that determines/supports my ability to access it in the midst of lots of stimulation or even crisis.  Also, the longer I go without attempting it, the harder it is to do next time -- like with any skill.  And here is where having a place solely dedicated to meditation is helpful.

And then, because I've been doing it for over 15 years, there's just more of a paved road there, it's as likely to happen as any thing else (and I'm sure there's some explanation connected to neurons or neural pathways in the brain to insert here if I knew squat about that.) But I think here is where I insert the importance of 'not-grasping' for this or any expereince. I had a taste of all this long before I meditated, so I didn't know what it was and was always trying to get it back - i.e. I didn't know about the whole 'non-clinging' thing then. So while I may have developed a 'paved road' - who knows how much time I spent hanging out there instead of investigating the nature of my experience to be free.

I have always wondered if we were all wired the same, but through Shinzen (and listening to hundreds of people report their experiences at retreat) I’ve come to realize that we are NOT all wired the same – at least in terms of the kinds of experiences we will have. But from working with you over the past...year or two? - I do tend to thing that we have 'similar wiring' - although you may be much more poetically articulate about your experience. :)

All that being said, now here’s my suggestion for you.  You said:

> Normally my blank screen is a chaotic soup of bright and dark micro-
> molecules, too small and too changing to single out and hold any one  
> particle

My suggestion is to go for holding the entire space (i.e. Shinzen’s ‘zooming out’ or ‘even coverage’) and not for ‘zooming in’ - i.e. collapsing space, as I do.  Allow that whole moving chaotic soup to just be a ‘flow version’ of your kasina.  For me, there’s something about the accepting of it as that (ok, the EQ word) that allows it to morph into the ‘stable’ kasina that is so restful and transporting (into the land of peace & bliss & absence of surface stuff.)

I know, you’re saying, why didn’t you just say that in the first place?  

But again, it is SO important to know that hanging out in any state is not the goal of this practice. Just resting in the 'blank' (as Shinzen puts it) field is a good practice.  Kasinas don't necessarily make things better, nor is your practice deeper, better if you experience them.  I know that having a blissful peaceful place to park sure sounds like a good goal, but just sitting AT ALL - even if your mind never stops - is a good practice.  

If you can sit with your overly-stimulated-from-god-knows-how-much-visual-imput-when-editing mind – with equanimity – so that the light show is just that, you’re ahead of the game, as far as I’m concerned.