user254: I started to read Mastering the Core Teachings of the Buddha (the PDF, version 3).
Before page 22, there's some text which says that (I paraphrase) sensations are fleeting and that consciousness-of-sensation is consciousness just of the echo of an already-previous sensation.
Then, on page 22, there's is a description of an exercise, which I quote below.
He introduces it as being "useful for jump-starting and developing insight into impermanence"; later, says that this same exercise promotes concentration and stability; and finally says that it was the only technique he used for five years.
Can you tell me more about this?
Is it some hybrid/mixture of insight and concentration?
Is it at unusual exercise? It seems to take 'two-pointed concentration' as its object, which I haven't ever read about before.
Are you aware of any specific advantages or disadvantages of this technique (or, whether and when it ought to be recommended or not recommended)?
Is there something it does well, too well, not well enough, not at all?

In one of these exercises, I sit quietly in a quiet place, close my eyes,
  put one hand on each knee, and concentrate just on my two index
  fingers. Basic dharma theory tells me that it is definitely not possible to
  perceive both fingers simultaneously, so with this knowledge I try to see
  in each instant which one of the two finger’s physical sensations are
  being perceived. Once the mind has speeded up a bit and yet become
  more stable, I try to perceive the arising and passing of each of these
  sensations. I may do this for half an hour or an hour, just staying with
  the sensations in my two fingers and perceiving when each sensation is
  and isn’t there. This might sound like a lot of work, and it definitely can
  be until the mind settles into it. It really requires the concentration of a
  fast sport like table tennis. This is such an engaging exercise and
  requires such precision that it is easy not to be lost in thought if I am
  really applying myself. I have found this to be a very useful practice for
  developing concentration and debunking the illusion of continuity. You
  can pick any two aspects of your experience for this exercise, be they
  physical or mental. I generally use my fingers only because through
  experimentation I have found that it is easy for me to perceive the
  sensations that make them up.
In another related exercise, I do the same sort of thing, sitting
  quietly in a quiet place with my eyes closed, but instead I concentrate on
  the sensations of the front and back of my head. With the knowledge
  that the illusion of a separate perceiver is partially supported by one
  impermanent sensation incorrectly seeming to perceive another
  impermanent sensation which it follows, such as the sensations in the
  back of the head incorrectly seeming to perceive the sensations of the
  front of the head which they follow, I try to be really clear about these
  sensations and when they are and aren’t there. I try to be clear if the
  sensations in the head are from the front or the back of the head in each
  instant, and then try to experience clearly the beginning and ending of
  each individual sensation.
This practice also requires a table tennis-like precision. Half an hour
  to an hour of this can be quite a workout until the mind speeds up and
  becomes more stable, but this sort of effort pays off. When I am
  engaged with this practice, there is little room to be lost in thought. I
  have also found this a very useful practice for developing concentration
  and debunking the illusion of continuity and the illusion of a separate
  self (more on that later).

The section ends with (one page 25),

For five years of my practice I was basically a One Technique Freak,
  and that technique was noticing how sensations flicker. I would do it as
  often as I could, i.e. basically whenever I didn’t have to be doing
  something that required concentration on the specifics of my life. I
  would be riding an elevator, just trying to see when I could feel each
  foot, or lying down to sleep and noticing how many times I could
  experience the sensations of my breath in each second. I also tried to
  notice this aspect of things for every single sensation that occurred
  during my formal practice. I used lots of objects, usually those that were
  presenting strongly at that time, and would use some variations on the
  above techniques as well as some others that I will mention shortly to
  keep me from getting stuck, but the aspect of my world that I tried to
  notice, things flickering, was always the same. I found that by making
  this sort of commitment to understanding one of the most basic
  assumptions of insight practices I was able to make fast progress and
  gain the ultimate insights I was looking for.


Earlier (e.g. on page 20 and 21) it was talking about becoming aware of some number of sensations per second ("maybe up to forty times per second") which he calls "vibrations", and combines with a breath meditation,

[...] It is also useful to check out exactly what happens at the
  bottom, middle, and top of the breath if you are using the breath as an
  object, and to examine if the frequency stays stable or changes in each
  phase of the breath. Never assume that what you have understood is the
  final answer! Be alert! Explore carefully and precisely with openness and
  acceptance! This is the door to understanding.
One last thing about vibrations: looking into vibrations can be a lot
  like any other sport. It can be thought of the way we might think of
  surfing or playing tennis, and this sort of game-like attitude can actually
  help a lot. We're “out to bust some vibrations!” as a friend of mine
  enthusiastically put it. [...]

I searched this site for the word "vibrations" thinking someone might have written something from this perspective already (if this were a well-known technique or "basic dharma theory"), but no, I don't see this mentioned in any previous topic.

user5191: This seems to me to just be the Goenka method of Vipassana restricted down even further in terms of where you direct your awareness. So in essence, a partial Satipatthana practice? He states you can do this with any physical or mental aspects, although I'm not sure how you would manage juggling mental objects like this. Perhaps this is just beyond my capacity.

Are you aware of any specific advantages or disadvantages of this technique (or, whether and when it ought to be recommended or not recommended)?

Having started my meditation "career" with a Goenka retreat, in my opinion at least, restricting awareness down like this can be helpful for a beginner, as you aren't bombarded all at once with having to be mindful of EVERYTHING that can arise. But it can also leave you unprepared for having to be mindful of really powerful emotional/mental stuff that WILL eventually make its way to the surface.

Is it some hybrid/mixture of insight and concentration?

It definitely does boost both faculties really well, in my experience.

user-1: 
He introduces it as being "useful for jump-starting and developing insight into impermanence"; later, says that this same exercise promotes concentration and stability; and finally says that it was the only technique he used for five years.
Can you tell me more about this?

It promotes concentration since it narrows the focus of the mind during the meditation practice -- it's not a single meditation object but the focus is still narrow. By resting the mind on specific experiences and making it the main interest of the mind it also helps weaken the hindrances, thus it promotes the stability.

Is it some hybrid/mixture of insight and concentration?

Yes. His main practice is insight, but because his focus is sufficiently narrow and on subtle experiences, his concentration also develops.

Is it at unusual exercise? It seems to take 'two-pointed concentration' as its object, which I haven't ever read about before.

I don't think it's unusual (in the sense of "unorthodox"). I think it's a sound experiment and exercise. Maybe having two fingers as his domain of interest is not too open ended (allowing him to develop enough concentration and use some degree of sharp penetration) but also not too narrow as to lose interest easily and sleep, e.g. by having sufficient/enough things going on to observe (and he says he finds this to be an engaging exercise). Maybe it also gives some base for contrasting experiences, helping to perceive the minutia of viññāṇa workings.

user5188: My take on what Daniel is trying to describe here is a deepening appreciation of the granularity of perception. The use of the word 'vibrations' in this context is a bit unorthodox hence your search coming up short. In some of Burmese Vipassana traditions, emphasis is placed on the experiencing of arising and passing of phenomena at very subtle levels. In this context this is a powerful insight practice into impermanence at a fundamental level - arising and (complete) cessation. Ajahn Brahm mentions this in Mindfulness, Bliss and Beyond (p. 203):

One now realizes that just as the stream of consciousness is granular, so is that component of the stream that is the citta. As noted earlier, sand on a beach appears continuous. Looking closely, however, one sees that the beach consists of tiny grains of silica. Looking even closer, one can see spaces between each grain, so that they aren’t even touching. The citta has this same granular quality. Instead of appearing as a continuous entity, it is now clearly recognized as made up of series of individual “knowings,” cittas or mind events, packed closely together and related to their neighbors by cause and effect. One can even discern that there is a gap between the mind events, between each knowing, where the citta has completely vanished from existence for a while.

Awareness of the granular nature of reality is not immediately obvious and Daniel's practice of the two-finger technique cleverly serves to concentrate the mind to notice at increasing frequency the arising of the perception one finger and then the other. Mahasi Sayadaw's noting technique has the same effect but is more open ended.

Is it at unusual exercise? It seems to take 'two-pointed concentration' as its object, which I haven't ever read about before.

I think this is an unusual practice. I certainly haven't seen reference to it anywhere else.

Is it some hybrid/mixture of insight and concentration?

This is Kanika Samadhi - moment-to-moment concentration.

Are you aware of any specific advantages or disadvantages of this technique (or, whether and when it ought to be recommended or not recommended)?

Like noting, I find the technique very useful in developing Kanika which in turn is essential for insight practice.
As a side note:- having been on a Goenka retreat myself, the use of the word 'vibrations' in a Goenka context is different. Goenka actively discourages noting as a technique. According to Goenka, noting increases our separation from raw sensate experience. From what I could glean from the Goenka discourses, what we experience at subtler and subtler levels beyond the gross bodily sensations are Kalapas (he actually uses this term and sticks to the Visuddhimagga doctrine that they extremely fast vibrations - billions of time per sec - of subtle reality). Our experience of these sensations at a body level has a vibratory quality to it.

254: <p>I started to read <em>Mastering the Core Teachings of the Buddha</em> (the PDF, version 3).</p>

<p>Before page 22, there's some text which says that (I paraphrase) sensations are fleeting and that consciousness-of-sensation is consciousness just of the echo of an already-previous sensation.</p>

<p>Then, on page 22, there's is a description of an exercise, which I quote below.</p>

<p>He introduces it as being "useful for jump-starting and developing insight into impermanence"; later, says that this same exercise promotes concentration and stability; and finally says that it was the only technique he used for five years.</p>

<p>Can you tell me more about this?</p>

<p>Is it some hybrid/mixture of insight and concentration?</p>

<p>Is it at unusual exercise? It seems to take '<em>two</em>-pointed concentration' as its object, which I haven't ever read about before.</p>

<p>Are you aware of any specific advantages or disadvantages of this technique (or, whether and when it ought to be recommended or not recommended)?</p>

<p>Is there something it does well, too well, not well enough, not at all?</p>

<blockquote>
  <p>In one of these exercises, I sit quietly in a quiet place, close my eyes,
  put one hand on each knee, and concentrate just on my two index
  fingers. Basic dharma theory tells me that it is definitely not possible to
  perceive both fingers simultaneously, so with this knowledge I try to see
  in each instant which one of the two finger’s physical sensations are
  being perceived. Once the mind has speeded up a bit and yet become
  more stable, I try to perceive the arising and passing of each of these
  sensations. I may do this for half an hour or an hour, just staying with
  the sensations in my two fingers and perceiving when each sensation is
  and isn’t there. This might sound like a lot of work, and it definitely can
  be until the mind settles into it. It really requires the concentration of a
  fast sport like table tennis. This is such an engaging exercise and
  requires such precision that it is easy not to be lost in thought if I am
  really applying myself. I have found this to be a very useful practice for
  developing concentration and debunking the illusion of continuity. You
  can pick any two aspects of your experience for this exercise, be they
  physical or mental. I generally use my fingers only because through
  experimentation I have found that it is easy for me to perceive the
  sensations that make them up.</p>
  
  <p>In another related exercise, I do the same sort of thing, sitting
  quietly in a quiet place with my eyes closed, but instead I concentrate on
  the sensations of the front and back of my head. With the knowledge
  that the illusion of a separate perceiver is partially supported by one
  impermanent sensation incorrectly seeming to perceive another
  impermanent sensation which it follows, such as the sensations in the
  back of the head incorrectly seeming to perceive the sensations of the
  front of the head which they follow, I try to be really clear about these
  sensations and when they are and aren’t there. I try to be clear if the
  sensations in the head are from the front or the back of the head in each
  instant, and then try to experience clearly the beginning and ending of
  each individual sensation.</p>
  
  <p>This practice also requires a table tennis-like precision. Half an hour
  to an hour of this can be quite a workout until the mind speeds up and
  becomes more stable, but this sort of effort pays off. When I am
  engaged with this practice, there is little room to be lost in thought. I
  have also found this a very useful practice for developing concentration
  and debunking the illusion of continuity and the illusion of a separate
  self (more on that later).</p>
</blockquote>

<p>The section ends with (one page 25),</p>

<blockquote>
  <p>For five years of my practice I was basically a One Technique Freak,
  and that technique was noticing how sensations flicker. I would do it as
  often as I could, i.e. basically whenever I didn’t have to be doing
  something that required concentration on the specifics of my life. I
  would be riding an elevator, just trying to see when I could feel each
  foot, or lying down to sleep and noticing how many times I could
  experience the sensations of my breath in each second. I also tried to
  notice this aspect of things for every single sensation that occurred
  during my formal practice. I used lots of objects, usually those that were
  presenting strongly at that time, and would use some variations on the
  above techniques as well as some others that I will mention shortly to
  keep me from getting stuck, but the aspect of my world that I tried to
  notice, things flickering, was always the same. I found that by making
  this sort of commitment to understanding one of the most basic
  assumptions of insight practices I was able to make fast progress and
  gain the ultimate insights I was looking for.</p>
</blockquote>

<hr>

<p>Earlier (e.g. on page 20 and 21) it was talking about becoming aware of some number of sensations per second ("maybe up to forty times per second") which he calls "vibrations", and combines with a breath meditation,</p>

<blockquote>
  <p>[...] It is also useful to check out exactly what happens at the
  bottom, middle, and top of the breath if you are using the breath as an
  object, and to examine if the frequency stays stable or changes in each
  phase of the breath. Never assume that what you have understood is the
  final answer! Be alert! Explore carefully and precisely with openness and
  acceptance! This is the door to understanding.</p>
  
  <p>One last thing about vibrations: looking into vibrations can be a lot
  like any other sport. It can be thought of the way we might think of
  surfing or playing tennis, and this sort of game-like attitude can actually
  help a lot. We're “out to bust some vibrations!” as a friend of mine
  enthusiastically put it. [...]</p>
</blockquote>

<p>I searched this site for the word "vibrations" thinking someone might have written something from this perspective already (if this were a well-known technique or "basic dharma theory"), but no, I don't see this mentioned in any previous topic.</p>
 5191: <p>This seems to me to just be the Goenka method of Vipassana restricted down even further in terms of where you direct your awareness. So in essence, a partial Satipatthana practice? He states you can do this with any physical or mental aspects, although I'm not sure how you would manage juggling mental objects like this. Perhaps this is just beyond my capacity.</p>

<blockquote>
  <p>Are you aware of any specific advantages or disadvantages of this technique (or, whether and when it ought to be recommended or not recommended)?</p>
</blockquote>

<p>Having started my meditation "career" with a Goenka retreat, in my opinion at least, restricting awareness down like this can be helpful for a beginner, as you aren't bombarded all at once with having to be mindful of EVERYTHING that can arise. But it can also leave you unprepared for having to be mindful of really powerful emotional/mental stuff that WILL eventually make its way to the surface.</p>

<blockquote>
  <p>Is it some hybrid/mixture of insight and concentration?</p>
</blockquote>

<p>It definitely does boost both faculties really well, in my experience.</p>
 -1: <blockquote>
<p>He introduces it as being &quot;useful for jump-starting and developing insight into impermanence&quot;; later, says that this same exercise promotes concentration and stability; and finally says that it was the only technique he used for five years.</p>
<p>Can you tell me more about this?</p>
</blockquote>
<p>It promotes concentration since it narrows the focus of the mind during the meditation practice -- it's not a single meditation object but the focus is still narrow. By resting the mind on specific experiences and making it the main interest of the mind it also helps weaken the hindrances, thus it promotes the stability.</p>
<blockquote>
<p>Is it some hybrid/mixture of insight and concentration?</p>
</blockquote>
<p>Yes. His main practice is insight, but because his focus is sufficiently narrow and on subtle experiences, his concentration also develops.</p>
<blockquote>
<p>Is it at unusual exercise? It seems to take 'two-pointed concentration' as its object, which I haven't ever read about before.</p>
</blockquote>
<p>I don't think it's unusual (in the sense of &quot;unorthodox&quot;). I think it's a sound experiment and exercise. Maybe having two fingers as his domain of interest is not too open ended (allowing him to develop enough concentration and use some degree of sharp penetration) but also not too narrow as to lose interest easily and sleep, e.g. by having sufficient/enough things going on to observe (and he says he finds this to be an engaging exercise). Maybe it also gives some base for contrasting experiences, helping to perceive the minutia of <em>viññāṇa</em> workings.</p>
 5188: <p>My take on what Daniel is trying to describe here is a deepening appreciation of the granularity of perception. The use of the word 'vibrations' in this context is a bit unorthodox hence your search coming up short. In some of Burmese Vipassana traditions, emphasis is placed on the experiencing of arising and passing of phenomena at very subtle levels. In this context this is a powerful insight practice into impermanence at a fundamental level - arising and (complete) cessation. Ajahn Brahm mentions this in Mindfulness, Bliss and Beyond (p. 203):</p>

<blockquote>
  <p>One now realizes that just as the stream of consciousness is granular, so is that component of the stream that is the citta. As noted earlier, sand on a beach appears continuous. Looking closely, however, one sees that the beach consists of tiny grains of silica. Looking even closer, one can see spaces between each grain, so that they aren’t even touching. The citta has this same granular quality. Instead of appearing as a continuous entity, it is now clearly recognized as made up of series of individual “knowings,” cittas or mind events, packed closely together and related to their neighbors by cause and effect. One can even discern that there is a gap between the mind events, between each knowing, where the citta has completely vanished from existence for a while.</p>
</blockquote>

<p>Awareness of the granular nature of reality is not immediately obvious and Daniel's practice of the two-finger technique cleverly serves to concentrate the mind to notice at increasing frequency the arising of the perception one finger and then the other. Mahasi Sayadaw's noting technique has the same effect but is more open ended.</p>

<blockquote>
  <p>Is it at unusual exercise? It seems to take 'two-pointed concentration' as its object, which I haven't ever read about before.</p>
</blockquote>

<p>I think this is an unusual practice. I certainly haven't seen reference to it anywhere else.</p>

<blockquote>
  <p>Is it some hybrid/mixture of insight and concentration?</p>
</blockquote>

<p>This is Kanika Samadhi - moment-to-moment concentration.</p>

<blockquote>
  <p>Are you aware of any specific advantages or disadvantages of this technique (or, whether and when it ought to be recommended or not recommended)?</p>
</blockquote>

<p>Like noting, I find the technique very useful in developing Kanika which in turn is essential for insight practice.</p>

<p>As a side note:- having been on a Goenka retreat myself, the use of the word 'vibrations' in a Goenka context is different. Goenka actively discourages noting as a technique. According to Goenka, noting increases our separation from raw sensate experience. From what I could glean from the Goenka discourses, what we experience at subtler and subtler levels beyond the gross bodily sensations are Kalapas (he actually uses this term and sticks to the Visuddhimagga doctrine that they extremely fast vibrations - billions of time per sec - of subtle reality). Our experience of these sensations at a body level has a vibratory quality to it.</p>
