Efficient Communication by Breathing

The arithmetic-coding-based communication system, Dasher, can be driven by a one-dimensional continuous signal. A belt-mounted breath-mouse, delivering a signal related to lung volume, enables a user to communicate by breath alone. With practice, an expert user can write English at 15 words per minute. Dasher is a communication system based on a beautiful idea from information theory called arithmetic coding (Witten et al., 1987; MacKay, 2003, Chapter 6). Arithmetic coding is an optimal method for text-compression using a language model. By turning arithmetic coding on its head, we obtain an optimal method for text-generation. We view a person’s gestures as a source of information, and the sentences they wish to communicate as the sink of information. Good interface design maximizes the number of bits per second that are conveyed from the user into text. Poor interfaces waste the user’s time either by failing to extract all the bits that the user could easily generate, or by diverting the user’s bits into redundant activity. The Dasher approach to interface design decouples the issues of efficient bit-generation and efficient language-generation. Unlike in most interfaces, a Dasher-user’s gestures have no relationship to particular symbols in the language. Instead, they control navigation in a continuous space whose contents are laid out using a language model. For demonstrations, or to try Dasher for yourself – it’s free – please visit www.inference.phy.cam.ac.uk/dasher/. The objective of this paper is to offer a new method for helping a disabled person to communicate by breath alone. In contrast to widely used switch-scanning systems, our method makes use of fine breathing control. Of course, not everyone has fine breath control, but to those who have, we would like to offer the chance to make use of that information, rather than discard it. 1 How Dasher works Imagine writing a piece of text by going into the library that contains all possible books, and finding the book that contains exactly that text. In this way, writing can be turned into a navigational task. What is written is determined by where the user goes. In Dasher’s idealized library, the ‘books’ are arranged alphabetically on one enormous shelf. When the user points at a part of the shelf, the view zooms in continuously on that part of the shelf. To write a message that