I was very much involved in electronics and engineering before becoming a psychologist, and still find that that kind of thinking, and the visual diagrams that often go with it, are useful to clarify my own understanding. Since I doubt that the way my mind works is unique to me, I'm sharing them here because I think they may be helpful to some other people.
Figure 1, below, illustrates what I call stabilizing concentration, the primary skill to be developed for various forms of concentrative meditation. Here I've drawn in a bunch of little figures marching across the page to illustrate the variety of sensations and experiences that ordinarily arise and flow through our minds as time goes by. If you close your eyes and just notice what happens, you'll find yourself thinking about this, going on to think about that, noticing a certain sensation, which reminds you of something or another, which memory is interrupted by another sensation, etc., etc., etc.,.
Figure 1: Stabilizing Concentration
In basic concentrative meditation, the instruction and the immediate goal is to focus your attention on a very narrow range of experience, a single kind of experience, as it were. The most common such focus object in world traditions is your breath. The sensation of breathing is always with us, and it's a relatively discrete kind of sensation, compared to more subtle things like thoughts and images, so you can pretty readily tell when you're actually paying attention to what your breathing feels like at the moment, versus drifting off on thoughts and memories. In the figure I've represented successful focus on the sensation of breathing as a series of dark ovals. Rather than attention being primarily caught up by the variety of experiences and sensations flowing in time, most of it, if not all of it, is on the sensation of breathing. This steadiness is symbolized by the solidity of the ovals representing breathing compared to the thinness of the other objects of experience.
Now it's very hard to be completely successful at this kind of concentrative meditation and have a sense of experiencing nothing but the focus point. So I've shown a break in concentration a little past the middle, for example, before a meditator notices she’s distracted and manages to pick up on following the desired focus again, the sensation of breathing in our example.
When most of us first attempt concentrative meditation, we find there is nothing to it, it’s easy --- for a breath or two --- and then a minute or two (or five or ten!) later, when we notice we’ve been thinking about dozens of other things than what we intended to concentrate on, we begin to realize how difficult this C-CAP of concentrative meditation is! Indeed, I've heard stories of many people who were shown how to do concentrative meditation and then complained that it made their mind race! The reality is that our mind is usually racing all the time, concentrative meditation practice doesn't make your mind race, it just makes us aware of that.
I've never been personally very good at concentrative meditation. Indeed years ago, after having tried a variety of meditations, taught by a variety of teachers, I gave up meditation. It seemed like all the various meditation instructions started with an admonition to first quiet your mind by doing something like just being aware of the breath, and then…. I could never get to the “and then” part, because my mind was always very busy, and I assumed that if I could not do this almost perfectly, what I was doing wasn’t worthwhile. In retrospect I can see my perfectionistic assumption was a mistake. But my attempts to meditate were pretty discouraging, so I gave it up, reasoning (rationalizing?) that some special talent was required to be a meditator and I didn’t have that special talent.
Although my personal experience is limited, I know from my study of Buddhism and other scientific and scholarly literature that some people get extremely good at concentrative meditation, they can stabilize their focus on some very limited aspect of experience, like their breath, very, very well. As a consequence of this, they may enter subtle altered states of consciousness (ASCs). The more they stabilize their concentration, the more ASCs they can experience, and the more profound these ASCs are. They are known as jhana states in Buddhism, and classically some eight of them are described in meditation texts. Other than mentioning that, I will say no more about the jhana states, as I don't really understand them.
I will note, though, that for those of us who are probably never going to make it to these jhanic "Olympics" of concentrative meditation, Buddhism doesn't consider it necessary to reach these high levels in order to successfully achieve enlightenment, although they can be helpful. What is required is a strong, but much less profound, ability to concentrate known as access concentration. This means your ability to focus and stabilize your attention is sufficient that you can begin using it to observe the nature of your mind more deeply, and so eventually bring about profound changes in its operation.
Difficulties of Self-Observation With Our Ordinary Mind:
There's a good analogy to this that I've heard from a number of teachers. Let your mind be represented by an underground cavern that has some fabulous and informative paintings and diagrams on its walls, information it would really help you to know. You, a seeker of Truth and self-knowledge, go down into that cavern, and you're carrying a little candle. Because there's a lot of wind (thoughts, emotions, sensations) funneling through the entrances to the cavern, and gusting wildly from moment to moment, your candle is almost blown out many times, and even when it stays lit, it's a small flame and it flickers very badly. This makes it very difficult to get clear observations of what any of these paintings and diagrams show. The access concentration you need to develop would be like being able to put a glass chimney around your candle to keep it shielded from the constantly blowing wind, then it could become a clearer, brighter, steadier flame – an aspect of stabilizing concentration - and so make observation much better. Looking around with this steadier lamp is a good analogy of the vipassana meditation, “insight meditation,” which we now turn to.
Concentration in Vipassana Meditation:
Figure 2 illustrates the process of vipassana meditation, in which the nature of the necessary concentration changes. While some ability to steady and stabilize concentration is still needed, what's really needed now is what I've dubbed in this figure knowing concentration,. Here you are not trying to hold your attention steadily on some limited aspect of reality, you're allowing those various experiences and sensations to arise and flow by as they will, minimizing, and hopefully eliminating, your interference with them. You don't try to focus on just on the ones you like and not notice the ones you don't like, nor try to make the “good” ones last longer or the “bad” ones to go away sooner, but instead try to use a kind of knowing concentration that lets you experience, see into, penetrate, each sensation that arises more openly, more accurately, and with equanimity.
Figure 2: Knowing Concentration in Vipassana
I'm not sure what the best term for this kind of “knowing” concentration is. "Penetrating" suggests the power to see more deeply into something, but could have negative connotations of forcing. I like the word Robert Heinlein coined in his famous novel, Stranger in a Strange Land, "grokking," with its implications of knowing something very deeply by becoming one with it, But I may be dating myself in using this word, and “becoming one with it sounds too mystical. Other terms like "opening up to" or “accepting," or "loving" could be applied. Every one conveys aspects of what I would like to convey, and all tend to have connotations that I'm not sure I want to convey.
Here's the various arrows representing concentrated attention reach out to the various arising aspects of experience and "penetrate" them, look more deeply into each one of them as it goes by, as, to use more classic Buddhist terms, as each arises, persists, and passes away. I've shown some aspects of experiences being missed in Figure 2, because when you learn vipassana, it takes a long time to be able to follow all aspects of experience. So in contrast to the stabilizing concentration of concentrative meditation, you are mainly not trying to keep your attention on one very specific, narrow aspect of experience, but allowing experience and sensation to arise in its full range of possibilities --- but looking deeply at each rising. Looking, as Shinzen Young aptly characterizes it, with concentration, clarity, and equanimity. Accepting what things are, not trying to change them, but trying to experience everything more deeply, to know each arising as it is.
(Incidentally I would add looking with an open curiosity, a factor I seldom see mentioned in classic Buddhist approaches – but that’s a story for some other time.)
I should note that I've given an idealized description of vipassana meditation here, an ability to experience anything with concentration, clarity, and equanimity, leading to deep insights into its nature and thus your nature. When first learning to practice vipassana, though, a smaller range of things will be focused on, such as the location of strong body sensations from moment to moment, or the qualities of sounds, as just two examples, so that it's easy to tell when you're actually following instructions and when your mind has drifted.
Figure 3, below, is expanding the diagrammatic representation of Figure 2 to give some idea of what happens when the knowing concentration developed in vipassana is working well. Here I’ve shown the arrows of knowing concentration penetrating and going through the risings in the flow of experience, so that different experiences are experienced more deeply, which I've represented by drawing them larger and giving them glowing colors. I'm not intending, of course, to say that everything experienced with knowing concentration becomes somehow "psychedelic," full all sorts of wonderful colors and qualities. That might happen sometimes, and sometimes an itch is really experienced much more fully as an itch! But to have the expectation that psychedelic-like changes will happen would lead to an incorrect practice of knowing concentration in vipassana, it would involve a desire to force experience into a certain kind of pattern, rather than to see each moment of experience for what it actually is. This (automatized – we do it habitually all the time) forcing of experience into desired patterns, instead of experiencing it as it really is, is the basis of not being enlightened in the first place.
Figure 3: Some Consequences of Successful Vipassana: Seeing More Clearly
OK, enough! My goal is starting to write this was not to say everything I know (or imagine I know) about meditation, but to highlight the differences in what kind of “concentration” is required in the two major styles of meditation, and I’ve done that to some degree. I hope it’s useful to some folks.