[colah]

Speaking in your head is called subvocalization (http://en.wikipedia.org/wiki/Subvocalization) and many forms of speed reading get the learner to eliminate it.

Subvocalization has several draw backs. One is that it is very bad at multitasking (eg. try reading this comment while counting).

It turns out that when you are subvocalizing, you send tiny impulses to your throat as though you are speaking, just not strong enough to do so. So it is possible to eavesdrop on subvocalization (NASA has experimented with this -- see wiki article).

Some people naturally don't subvocalize because of learning disabilities; they usually have trouble writing and speaking because they have to translate their thoughts into English.

Of course the idea that you are thinking in a language is rather terrifying. Consider how it is moulding your thoughts. The idea that language effects your thoughts is called the Sapir-Whorf hypothesis. (Some people have tried to make better languages to think in, see lojban.)

I find it interesting to note that when I program, I think, at least partially, in that language -- I've even noticed that I attach sounds to some operators in C. I also notice that the way I think varies depending on the area of math I'm working in: when I am doing algebra or calculus, it's a combination of subvocalized math and visualisation of formulas, whereas complex analysis is often almost entirely visual and set theoretic topology often is neither subvocalized or visualised.

/rant

[pbhjpbhj]

I gather that subvocalisation also is accompanied by eye movement and some facial muscle activity and that this is used by mentalists like Derren Brown. For example the way the eyes look can show if one is thinking about something in the future or past (although it doesn't work on everyone and I think is culture dependent).

If Sapir-Whorf holds true then we should see those using a specific language excelling in specific areas shouldn't we? Could this perhaps account for some of the stereotypical characteristics we ascribe to different nationalities.

[est]

Subvocalization is and interesting idea, but it's more about how to encoding information into your brain, how about the decoding process? For instance when you write an English essay can you finish it without a speaking voice in your head?

And oh yes, we all think in formulas when doing mathematics. I have problem vocalizing formulas with Greek letters to others but I can quickly write them down. I think it's because Greek letters were never officially taught in China.