I've recently encountered the same meditative technique on two separate occasions.
First, I was listening to this song, which included an excerpt from an Alan Watts speech as the lyrics:
I found the full transcript of the speech here.
This is the part of the speech that is resonating with me:
"The easiest way to get into the meditative state is to begin by listening. If you simply close your eyes, and allow yourself to hear all the sounds that are going on around you. Just listen to the general hum and buzz of the world. As if you were listening to music. Don’t try to identify the sounds you are hearing, don’t put names on them. Simply allow them to play with your eardrums. Don’t judge the sounds. There are no, as it were, proper sounds or improper sounds, and it doesn’t matter if somebody coughs or sneezes or drops something. It’s all just sound."
"And if I am talking to you right now and you are doing this, I want you to listen to the sound of my voice just as if it were noise. Don’t try to make any sense out of what I’m saying, because your brain will take care of that automatically. You don’t have to try to understand anything, just listen to the sound."
"As you pursue that experiment, you will very naturally find that you can’t help naming sounds, identifying them, that you will go on thinking. That is to say, talking to yourself inside your head automatically. But it’s important that you don’t try to repress those thoughts by forcing them out of your mind. Because that will have precisely the same effect as if you were trying to smooth rough water with a flat iron. You’re just going to disturb it all the more."
"What you do is this: as you hear sounds coming up in your head, thoughts, you simply listen to them as part of the general noise going on just as you would be listening to the sound of my voice or just as you would be listening to cars going by or two birds chattering outside the window. So look at your own thoughts as just noises. And soon you will find that the so-called outside world and the so-called inside world come together. They are a happening. Your thoughts are happening, just like the sounds going on outside, and everything is simply a happening and all you’re doing is watching it."
The second occasion on which I encountered this same technique for meditation was during a group meditation at the San Francisco Zen Center.
The Zen teacher guided us in a meditation that involved focusing on the feeling of our bodies, focusing on the sounds that we could hear, focusing on our thoughts, and then focusing on our thoughts as just sounds.
I wonder if this meditative technique is particular to Zen. I believe Zen is the spiritual tradition that Watts followed.
My understanding
I'm someone who struggles to slow down my mind. I seem to have a high rate of thoughts flowing through my head at any given time. And I tend to give each thought attention, rather than letting it flow in one ear and out the other.
For my work, I'll think of something I need to do and then I'll have successive thoughts about how I will do it and when I will do it. For my writing, I'll start thinking of the first few lines of a poem and then I'm already thinking of the fourth and fifth lines, trying to make a complete poem.
Likening thoughts to sounds is a helpful idea that has recently been allowing me to let go of my thoughts more easily.
It doesn't stop me from having the initial thought. I don't think it's possible or healthy to stop the initial thought. But it allows me to not have the second and third successive thoughts. When I think the initial thought, I don't try to analyze it or break it apart, I do my best just to regard it as it is.
The analogy to sounds is helpful because it teaches me to let thoughts go in the same way that I let sounds go.
For example, as I write this, I'm at my desk in the apartment and a truck just drove up the hill outside. I heard the sound and my brain immediately realized that it was a truck going up the hill, but I didn't give it any more attention. I didn't ask myself, what type of truck? Where is the truck going? On and on.
If I can get into the habit of regarding thoughts similar to how I regard sounds, I think this will make it easier for me to think fewer successive thoughts after initial thoughts. The goal is to think the initial thought, be aware of it, and then let it go.