user11674: Is it during deep meditation when the mind is completely stilled that one experiences anatta? Is the conviction in anatta gradual or abrupt? This question would be connected to the 4 stages of enlightenment, too.
Regards

user111: Anatta can be seen even by the average Joe. Ex: when there's headache or any kind of bodily pain, why it is not going away at will?  When you taste something, why the taste disappear after eating? Why can't you make the taste persist. Why your body stink when you don't take bath? Why can't you stop that from happening? When happiness arises in the mind, why does it fade away without your consent?

user23484: Thought I'dd add on to your question. There is no "how" in terms of a process that can be solely led by consciousness, meaning you have to cultivate your mind through the eightfold practice, as to allow this insight to bloom on its own. Insight is bhavana maya panna (wisdom obtained by meditation practice). It happens on its own, when conditions are ripe. But for bhavana maya panna to arise, you need first two others kinds of wisdom. First - suta mayapanna, external wisdom you get from listing to others or reading buddhist texts, quick note - it is enough to read or get instructed about anicca, anatta and dukkha. Second - comes cinta mayapanna knowledge derived from one's own thinking about these themes, trying to structure them for oneself or better, trying to develop intellectual grasp on them ( intellectual may be too narrow term, as you develop both intellectual and emotional grasp on thought about things, as mind sense base deals with both thoughts, emotions, sense impressions and volitions ie invisible stuff). So with enough of both of these types of panna the panna conditions are ripe , and when other conditions are met bhavana mayapanna arises. One of the type of this wisdom that can arise is direct insight (equaling at the moment direct experience) of anatta.
What are the other conditions? general answer might be being on par with the whole eightfold path. But since I can speak only of my own experience, the main practice that I do are the sattipattanas, with main focus on vedananupassana, cittanupassana and parts of dhammanupassana. As such the other conditions would be balancing five mental faculties to be present (panna in first two types described before, and sati,  samadhi, viriya, saddha - awareness, stability of the mind, perseverance, and faith).
However I have experienced anatta both in sati based practises (sattipatanas in my own case) and samadhi states that followed these practises, so again I'd say the type practice doesnt really matter, what matters is is getting the conditions right.
Also had the opportunity to experience it in daily life, when the momentum of practice was strong. Have not experienced anatta in metta practice, but Im looking forward to it.
As to the experience itself I'd describe it as removing the axis of the turning wheel, but the wheel of phenomena is still turning, where axis is "you" and "yours" or I making and mine making. So these drop, but physical sensations, thoughts emotional states and volitions continue on their own.
hope this personal take from a fellow yogi helps a bit. also: your experience of anatta might be worded differently, but there will be no doubt about the taste of experience itself . language is an obstacle when trying to communicate these things :D

user471: If by "experiencing anatta", you mean overcoming self-view or identity-view (sakkaya ditthi), then you do not need a very deep meditation experience, from my understanding.
On the other hand, if by "experiencing anatta", you mean overcoming the "I am" conceit, the "I am" obsession and the "I am" desire, then yes, you need a deeper cleansing to get the odor out.

"In the same way, friends, it's not that I say 'I am form,' nor do I
say 'I am other than form.' It's not that I say, 'I am feeling...
perception... fabrications... consciousness,' nor do I say, 'I am
something other than consciousness.' With regard to these five
clinging-aggregates, 'I am' has not been overcome, although I don't
assume that 'I am this.' ....
"Just like a cloth, dirty & stained: Its owners give it over to a
washerman, who scrubs it with salt earth or lye or cow-dung and then
rinses it in clear water. Now even though the cloth is clean &
spotless, it still has a lingering residual scent of salt earth or lye
or cow-dung. The washerman gives it to the owners, the owners put it
away in a scent-infused wicker hamper, and its lingering residual
scent of salt earth, lye, or cow-dung is fully obliterated.
"In the same way, friends, even though a noble disciple has abandoned
the five lower fetters, he still has with regard to the five
clinging-aggregates a lingering residual 'I am' conceit, an 'I am'
desire, an 'I am' obsession. But at a later time he keeps focusing on
the phenomena of arising & passing away with regard to the five
clinging-aggregates: 'Such is form, such its origin, such its
disappearance. Such is feeling... Such is perception... Such are
fabrications... Such is consciousness, such its origin, such its
disappearance.' As he keeps focusing on the arising & passing away of
these five clinging-aggregates, the lingering residual 'I am' conceit,
'I am' desire, 'I am' obsession is fully obliterated."
SN 22.89


user43: Update 2022. You don't experience Anatta. You just don't experience the illusion of self anymore.
Original answer:
I remember back in ~2001 I was very serious about this topic -- trying to experience anatta first-hand.
Back then I already did ~3 years of the non-attachment practice, as a result I no longer identified myself with my thoughts, but I still could not see how the watcher and the thinker of thoughts was not real.
The way I got first-hand experience of "no-subject" was through meditation on "chitta-vritti" or the train-of-thoughts process. I was watching my thoughts very closely, trying to see where they come from... and how they dissolve...
As I kept watching, I saw that thoughts do not really dissolve, instead they are slowly replaced by the next thought. When I focused on this process of replacement of one thought by the next, I realized that the very "I who is watching this process" was in fact nothing else but the next thought itself(!)
What I clearly saw from this process is that what we normally assume to be the fixed subject of experience is actually transient! Every next thought serves as subject of the previous thought, until it becomes object of the next thought which at that moment is the subject etc.
This is when it became very clear to me that thoughts work by the principle of association. There is nothing like "subject" that "thinks the thoughts" and decides what to do. The mind works by associating the current experience with the memories we had from the previous experiences and coming up with the most appropriate response(s). As I watched myself during day-to-day action, in light of this realization, it became more and more clear to me, that the idea of "I" is something we are trained to overlay on top of the otherwise automatic process. It's a useful trick that helps us explain our choices to other people: "I did X because I wanted Y" or "I said A because I remembered B" - but in reality all this wanting, decision making, doing and thinking - happens automatically through association. The more I watched myself acting, day by day, the more clearly I saw that there was no "I" that acted, the action happened by itself. The more I watched other people, the more I saw that they too respond automatically. (This last realization actually helped me be more effective with people. I stopped expecting them to be objective or reasonable, and accepted that their actions came from their biases and preconceptions.)
An obvious question one can ask at this point: but what about the freedom of will then, is that an illusion? And how do we reconcile this with Buddha's insisting that we must act skillfully and take responsibility? It's alright and still true. Both are valid perspectives on the same reality. Whether automatically or not, acting skillfully still matters. Even if I am an automatic biological robot responding automatically based on my past experience - still, if I make bad decisions, cultivate laziness, sloppiness, bad mental and physical hygiene, let negative mindstates grow - I will suffer the consequences of my actions. Even if they are not truly "my" actions, the experience of results will be "mine". And if I make good decisions, cultivate will power, excellence, good mental and physical hygiene, positive mindstates - there will be experience of those results in due time. Even though the subject of that experience is just the next transient thought and not any fixed "I" - the experience will be real at that point.
So my answer is: anatta can be directly experienced in meditation on chitta-vritti, by closely watching the train-of-thoughts process. It can then be further clarified by watching one's thoughts and actions objectively in post-meditation, to disidentify from one's opinions, biases, and attachments. Care should be taken to not allow the experience of anatta degenerate into an attitude of fatalism, meekness, and laziness.

11674: <p>Is it during deep meditation when the mind is completely stilled that one experiences anatta? Is the conviction in anatta gradual or abrupt? This question would be connected to the 4 stages of enlightenment, too.</p>

<p>Regards</p>
 111: <p>Anatta can be seen even by the average Joe. Ex: when there's headache or any kind of bodily pain, why it is not going away at will?  When you taste something, why the taste disappear after eating? Why can't you make the taste persist. Why your body stink when you don't take bath? Why can't you stop that from happening? When happiness arises in the mind, why does it fade away without your consent?</p>
 23484: <p>Thought I'dd add on to your question. There is no &quot;how&quot; in terms of a process that can be solely led by consciousness, meaning you have to cultivate your mind through the eightfold practice, as to allow this insight to bloom on its own. Insight is bhavana maya panna (wisdom obtained by meditation practice). It happens on its own, when conditions are ripe. But for bhavana maya panna to arise, you need first two others kinds of wisdom. First - suta mayapanna, external wisdom you get from listing to others or reading buddhist texts, quick note - it is enough to read or get instructed about anicca, anatta and dukkha. Second - comes cinta mayapanna knowledge derived from one's own thinking about these themes, trying to structure them for oneself or better, trying to develop intellectual grasp on them ( intellectual may be too narrow term, as you develop both intellectual and emotional grasp on thought about things, as mind sense base deals with both thoughts, emotions, sense impressions and volitions ie invisible stuff). So with enough of both of these types of panna the panna conditions are ripe , and when other conditions are met bhavana mayapanna arises. One of the type of this wisdom that can arise is direct insight (equaling at the moment direct experience) of anatta.
What are the other conditions? general answer might be being on par with the whole eightfold path. But since I can speak only of my own experience, the main practice that I do are the sattipattanas, with main focus on vedananupassana, cittanupassana and parts of dhammanupassana. As such the other conditions would be balancing five mental faculties to be present (panna in first two types described before, and sati,  samadhi, viriya, saddha - awareness, stability of the mind, perseverance, and faith).
However I have experienced anatta both in sati based practises (sattipatanas in my own case) and samadhi states that followed these practises, so again I'd say the type practice doesnt really matter, what matters is is getting the conditions right.
Also had the opportunity to experience it in daily life, when the momentum of practice was strong. Have not experienced anatta in metta practice, but Im looking forward to it.
As to the experience itself I'd describe it as removing the axis of the turning wheel, but the wheel of phenomena is still turning, where axis is &quot;you&quot; and &quot;yours&quot; or I making and mine making. So these drop, but physical sensations, thoughts emotional states and volitions continue on their own.</p>
<p>hope this personal take from a fellow yogi helps a bit. also: your experience of anatta might be worded differently, but there will be no doubt about the taste of experience itself . language is an obstacle when trying to communicate these things :D</p>
 471: <p>If by &quot;experiencing anatta&quot;, you mean overcoming self-view or identity-view (<em>sakkaya ditthi</em>), then you do not need a very deep meditation experience, from my understanding.</p>
<p>On the other hand, if by &quot;experiencing anatta&quot;, you mean overcoming the &quot;I am&quot; conceit, the &quot;I am&quot; obsession and the &quot;I am&quot; desire, then yes, you need a deeper cleansing to get the odor out.</p>
<blockquote>
<p>&quot;In the same way, friends, it's not that I say 'I am form,' nor do I
say 'I am other than form.' It's not that I say, 'I am feeling...
perception... fabrications... consciousness,' nor do I say, 'I am
something other than consciousness.' With regard to these five
clinging-aggregates, 'I am' has not been overcome, although I don't
assume that 'I am this.' ....</p>
<p>&quot;Just like a cloth, dirty &amp; stained: Its owners give it over to a
washerman, who scrubs it with salt earth or lye or cow-dung and then
rinses it in clear water. Now even though the cloth is clean &amp;
spotless, it still has a lingering residual scent of salt earth or lye
or cow-dung. The washerman gives it to the owners, the owners put it
away in a scent-infused wicker hamper, and its lingering residual
scent of salt earth, lye, or cow-dung is fully obliterated.</p>
<p>&quot;In the same way, friends, even though a noble disciple has abandoned
the five lower fetters, he still has with regard to the five
clinging-aggregates a lingering residual 'I am' conceit, an 'I am'
desire, an 'I am' obsession. But at a later time he keeps focusing on
the phenomena of arising &amp; passing away with regard to the five
clinging-aggregates: 'Such is form, such its origin, such its
disappearance. Such is feeling... Such is perception... Such are
fabrications... Such is consciousness, such its origin, such its
disappearance.' As he keeps focusing on the arising &amp; passing away of
these five clinging-aggregates, the lingering residual 'I am' conceit,
'I am' desire, 'I am' obsession is fully obliterated.&quot;<br />
<a href="https://www.accesstoinsight.org/tipitaka/sn/sn22/sn22.089.than.html" rel="nofollow noreferrer">SN 22.89</a></p>
</blockquote>
 43: <p>Update 2022. You don't experience Anatta. You just don't experience the illusion of self anymore.</p>
<p>Original answer:</p>
<p>I remember back in ~2001 I was very serious about this topic -- trying to experience <code>anatta</code> first-hand.</p>
<p>Back then I already did ~3 years of the non-attachment practice, as a result I no longer identified myself with my <em>thoughts</em>, but I still could not see how the <em>watcher</em> and the <em>thinker</em> of thoughts was not real.</p>
<p>The way I got first-hand experience of &quot;no-subject&quot; was through meditation on &quot;chitta-vritti&quot; or the train-of-thoughts process. I was watching my thoughts very closely, trying to see where they come from... and how they dissolve...</p>
<p>As I kept watching, I saw that thoughts do not really dissolve, instead they are slowly <em>replaced</em> by the next thought. When I focused on this process of replacement of one thought by the next, I realized that the very &quot;I who is watching this process&quot; <em>was in fact nothing else but the next thought itself</em>(!)</p>
<p>What I clearly saw from this process is that <strong>what we normally assume to be the fixed subject of experience is actually transient!</strong> Every next thought serves as subject of the previous thought, until it becomes object of the next thought which at that moment is the subject etc.</p>
<p>This is when it became very clear to me that thoughts work by the principle of association. There is nothing like &quot;subject&quot; that &quot;thinks the thoughts&quot; and decides what to do. The mind works by associating the current experience with the memories we had from the previous experiences and coming up with the most appropriate response(s). As I watched myself during day-to-day action, in light of this realization, it became more and more clear to me, that the idea of &quot;I&quot; is something we are trained to overlay on top of the otherwise automatic process. It's a useful trick that helps us explain our choices to other people: &quot;I did X because I wanted Y&quot; or &quot;I said A because I remembered B&quot; - but in reality all this wanting, decision making, doing and thinking - happens automatically through association. The more I watched myself acting, day by day, the more clearly I saw that there was no &quot;I&quot; that acted, the action happened by itself. The more I watched other people, the more I saw that they too respond automatically. (This last realization actually helped me be more effective with people. I stopped expecting them to be objective or reasonable, and accepted that their actions came from their biases and preconceptions.)</p>
<p>An obvious question one can ask at this point: but what about the freedom of will then, is that an illusion? And how do we reconcile this with Buddha's insisting that we must act skillfully and take responsibility? It's alright and still true. Both are valid perspectives on the same reality. Whether automatically or not, acting skillfully still matters. Even if I am an automatic biological robot responding automatically based on my past experience - still, if I make bad decisions, cultivate laziness, sloppiness, bad mental and physical hygiene, let negative mindstates grow - I will suffer the consequences of my actions. Even if they are not truly &quot;my&quot; actions, the experience of results will be &quot;mine&quot;. And if I make good decisions, cultivate will power, excellence, good mental and physical hygiene, positive mindstates - there will be experience of those results in due time. Even though the subject of that experience is just the next transient thought and not any fixed &quot;I&quot; - the experience will be real at that point.</p>
<p>So my answer is: <code>anatta</code> can be directly experienced in meditation on chitta-vritti, by closely watching the train-of-thoughts process. It can then be further clarified by watching one's thoughts and actions <em>objectively</em> in post-meditation, to disidentify from one's opinions, biases, and attachments. Care should be taken to not allow the experience of anatta degenerate into an attitude of fatalism, meekness, and laziness.</p>
