In writing an essay I'm working on about why hard disk video recorders are as novel as they are, I explored a concept I think is worthy of its own blog entry. This is the concept of Telepathic User Interface or TUI.
A TUI is a user interface that you use so much that it becomes unconscious. Perhaps the classic TUI is touch typewriter keyboard. I just think letters and they simply come out. I am no longer consious of the mechanism. In many cases I think sets of letters and even words and they just come out. From the mind to the computer -- telepathic.
Other examples include the car. After you drive a car for a while it becomes an extension of yourself. Learning the clutch is hard but soon you are not thinking about it at all. And the remote control on a Tivo, I write in the essay, has aspects of a TUI -- you learn how to move around a program without thinking.
A TUI is not always a natural interface or even a good interface. It's just one you use often enough to make it subconsious. It doesn't have to be intuitive -- an intuitive interface is simply one that's easy to guess the operation of.
When it comes to computer software, this helps us understand the dichotomy between the GUI/WIMP style and the command line and keyboard style which still has many devotees.
GUI interfaces are easy to learn, and easy to guess. And of course for positional inputs they are markedly superior and often the only choice. But by and large, the story of Mice and Menus took a path away from the TUI. You have to focus your eyes on the pointer in order to use a GUI, and you have to read to use a menu. It's much more difficult to use such a system unconsiously. (Mouse gesture interfaces change that a bit.)
Fans of text editors like VI and Emacs, with complex, non-intuitive keyboard interfaces love them because they have reached TUI state, at least in part. Many of the operations have become unconsious, and thus much faster and easier as far as the user is concerned.
Command line interfaces are never completely TUI, but they take advantage of the TUI nature of touch-typing. Because touch typing maps words from brain to screen, complex commands can have a fair bit of TUI to them.
It is a rare technology that can earn a TUI. You need to be using it a great deal, and regularly. Video games also develop TUIs because of their devotion. And while it doesn't seem to matter how intuitive the interface is, since many users will never attain the TUI state with a program, that's no excuse for trying to be more intuitive and easy to handle.
On the other hand, programs that don't provide keyboard shortcuts and other muscle-memory schemes for doing things will never develop a TUI, no matter how heavily used they are. Who changes a font in the Excel spreadsheet without being conscious of all the steps they are taking?