Covering your mouth like that is instinctive. It signals “I’m listening/thinking, not talking”. It’s encouragement for the speaker to keep going.

I read about this in a book on body language by Allan Pease.

I hope someone with expertise will provide a better answer, but since there’s none yet I’ll give my intuition.

It’s a signal. It tells whoever you’re interacting with that you’re doing stuff in your head, so they know you’re listening, that you’re thinking of an answer or something like that.

Imagine how weird it’d be if we didn’t do that. You say something to a person and they just stare at you without moving a muscle for a few seconds before reacting. You’d think there’s something wrong with them

Yes, it’s cultural. Using your hands to think in general is natural, just like head movements - but the actual movements we use are cultural

There’s some natural shaping to the movements, such as tilting your head to signal you’re paying close attention - tilting your head can help you hear more clearly. In the same way, covering your lips in some way signals you’re not trying to speak

But ultimately, in another timeline everyone would be bobbing their head from side to side to signal consideration… It’s shaped by instinct to some extent, but dominated by culture

People like to think of themselves as an individual…

But we’re not. And not just the brain having different parts that may conflict, we have different parts of our body running on autopilot using their own axons and nerves.

Proprioception is one of “extra” senses that everyone has but isn’t in the five basic ones were taught in highschool.

It’s how we can reflexively catch something without needing to see it falling, recognize what’s happening, and decide to catch it.

But that system isn’t just split second reflexes, it’s why we can walk and chew gum at the same time or can ride a bike without paying attention and daydream.

Sometimes that system wants input, but it can’t communicate to your consciousness, it’s not hooked up to the language center to pop a thought into your head.

So it puts your body/limbs into a “thinking position” and your conscious mind starts trying to logic out whatever problem it’s aware of. Hopefully it’s the one giving your body pause.

Like, that’s the whole “oneness” people talk about trying to achieve thru meditation and shit. Getting not just conscious and the various unconscious parts of your mind on the same page, but getting all the independent pieces of your entire body on the same page.

Like the monks who can raise/lower body temp at will. It’s sounds supernatural unless you actually understand how a human is put together, then it’s just a party trick like wiggling your ears. Anyone could learn to do it, but the action isn’t the point, it’s an exercise in getting all the parts of your body to follow the same game plan.

So, less a signal to others that we’re thinking, and more a sign from our body that we need to take a beat and think before acting. For people that think of every human as a single individual, it’s a weird thought. But a human is less an individual and more like an aircraft carrier crammed with thousands of people, who hopefully are all working towards the same goal.

I think you’ve pretty much got it. It’s a way to communicate that you’re thinking hard. It helps the speaker know what effect they’re having on the audience - if a lot of people looked confused or bored, the lecturer might adjust their delivery.

No answer, but I wonder if it’s more than conditioning. At times when I’m thinking, with others or alone, I mash my hand to my chin/lower lip. I don’t feel I’m indicating anything, but I swear it helps with ideas.