The longer explanation

Imagine a library containing all possible books, ordered alphabetically on a single shelf. Books in which the first letter is “a” are at the left hand side. Books in which the first letter is “z” are at the right. In picture (i) below, the shelf is shown vertically with “left” (a) at the top and “right” (z) at the bottom. The first book in the “a” section reads “aaaaaaaaaaaa…"; somewhere to its right are books that start “all good things must come to an end…"; a tiny bit further to the right are books that start “all good things must come to an enema…”.

(i)	(iii)	(iii)

When someone writes a piece of text, their choice of the text string can be viewed as a choice of a book from this library of all books - the book that contains exactly the chosen text. How do they choose that book? Let’s imagine they want to write “all good things…”

First, they walk into the “a” section of the library. There, they are confronted by books starting “aa”, “ab”, “ac,…. “az” [Picture (ii)]. Looking more closely at the “al” section, they can find books starting “ala”, “alb”,… “alz” [Picture (iii)].

By looking ever more closely at the shelf, the writer can find the book containing the text he wishes to write. Thus writing can be described as zooming in on an alphabetical library, steering as you go.

This is exactly how Dasher works, except for one crucial point …

Part two

…. This is exactly how Dasher works, except for one crucial point: we alter the SIZE of the shelf space devoted to each book in proportion to the probability of the corresponding text. For example, not very many books start with an “x”, so we devote less space to “x…” books, and more to the more plausible books, thus making it easier to find books that contain probable text.

Here is the corresponding sequence of pictures of the library in Dasher. (The character “_” denotes the space character.)

(i)	(iii)	(iii)

Dasher can be trained on examples of any writing style, and it learns all the time, picking up your personal turns of phrase.

Demonstrations

The image below shows the state of the Dasher interface while the user is writing the word `objection'; alternative words that could easily be written at this point include `objective', `objects_', and `object_oriented'.

If you find Dasher hard to imagine based on these static pictures, please take a look at the movies below. When you watch someone else steering Dasher, you may find it looks difficult, but be assured: it is actually very easy; it’s a lot like driving a car.

You can try Dasher right now, in your browser, if your browser is Java-enabled.

When you try Dasher for the first time, please read the tips for novices.

Streaming movies, presentations

By the Dasher team

Dasher - information-efficient text entry (19th April 2007)

Google tech talk (54 minute video) by David MacKay at Google Inc, Mountain View

By other people

Augie, an ALS-sufferer, is featured on this MSNBC article - we see him driving Dasher with his feet.

Google video by Paul Tingey showing Dasher hooked up to RoboRealm (machine vision software)

“Writing sentences with a red plastic ball”

Movies

Simple movies

File size

Animated gif of Dasher version 3, should work in any browser

300K

Animated gif of Dasher version 3, identical to the above, but higher quality animation

560K

Animated gif of Dasher version 1, should work in any browser

81K

Animated gif of Daishoya (Japanese Dasher version 1).
    Further information in Japanese

300K

Flash movie (will play in your browser if flash-enabled) showing Dasher in Persian

by Behdad and the FarsiWeb Project

Movies for Windows systems

File size

Streaming video demonstration (1.5 mins asf) including audio commentary.
    The text of the commentary is available.

2.7 M

3 minute demonstration of Dasher, with a commentary. The demonstration uses lotus screen cam software (included in the zip file) which runs on windows 95 systems.
This movie is highly recommended as the commentary explains how Dasher is used.

5 M

    The text of the commentary is available.

4 K

mpeg Movies

File size

Dasher with an eye-tracker: enhanced eyetracking mode (Aug 2005)

28 M

Dasher with an eye-tracker (November 2001)

6 M

[In this movie, David hits the space bar to start the program going, and after that he uses nothing but eyes; he’s using Dasher version 1.6. In Dasher versions 3 and 4, we can start and stop Dasher without cheating in this way.]

Dasher running on a Compaq iPAQ

9 M

Dasher with an eye-tracker: enhanced eyetracking mode, demonstrating autocalibration, within ten seconds or so, of a hugely-miscalibrated eyetracker (September 2004)

17 M

Dasher with an eye-tracker: enhanced eyetracking mode, demonstrating use of control mode (September 2004)

9 M

Breath Dasher, including control mode demonstration (September 2004)

25 M

Keith Vertanen’s Speech-Dasher prototype (mpg) (avi)

13 M

Large MOV Movies

File size

Large AVI Movies

File size

Dasher with an eye-tracker (November 2001)

54 M

AVI of Dasher running on a Compaq iPAQ

4 M

Very large AVI of Dasher running on a Compaq iPAQ

90 M

AVI by Alexandre-Alapetite showing Dasher being used to write rich text into a Wiki

3M

Daniel Jalkut’s movie of Dasher on a Mac can be found on this blog

28M

More screenshots with captions can be found here and here. For further demonstrations, movies and screenshots see David Ward’s Dasher site; also Keith Vertanen’s.

Thanks to Steve Hiner, Geoff Stead, and Simon Cozens for help with animations.