Technotes: Braille Displays
Transitory Braille displays provide access to PCs but the displays are different from speech output. Braille is a notation tracking a cursor, and reading the screen and routing are accomplished by the fingers moving across raised dots. This article describes the technology utilized by transitory, or refreshable, braille computer displays.
Louis Braille (1809-1852) developed a code that is read by fingers moving across a series of raised dots. Braille has come into use worldwide, and can even be used in those languages that have pictorial alphabets, as well as in languages with phonetic- based alphabets.
With dedicated programs the transcription of text into Braille can--to some degree--be handled automatically through Braille printers that emboss Braille on paper. Braille is a useful alphabet for blind people when they use computers. The design of Braille displays and their common features are described below. Besides speech-based interaction, Braille is a good alternative for those who have learned to read it, and the combination of Braille and screen-readers is beneficial for many people. The initial cost for a Braille display (compared to a text-to-speech synthesizer) may be worthwhile in the workplace, because it offers faster interaction with standard MS-DOS software (Espinola & Croft, 1992).
Let's look at an example where a student learns Braille Grade I and contracted Braille (Grade II) in her native language. If she takes courses in mathematics, chemistry, music or foreign languages, she also needs to learn the proper notation used in these subjects. Of course, the core alphabet remains the same but special symbols are added (for example an integral sign in mathematics or punctuation marks that differ between European and U.S. Braille).
Each character in six-dot Braille consists of a combination of raised (and lowered) dots in a (2,3) matrix. Figure 1 gives an example. Touchable (raised) dots are drawn with the character 'o', untouchable dots are marked with a period. Above each Braille cell the corresponding print character is shown. The first character in Fig.1 announces the capital B character. Six-dot Braille codes use other "escape characters" to enlarge the character set.
.o o. o. o. .o o. o. o.
.. o. oo .. o. o. o. .o
.o .. o. .. .. o. o. ..
Fig.1: Sample text "Braille" in German six-dot Braille
An appropriate Braille display working as a computer terminal shows every character in Braille on a one-to-one basis as it would appear in print on a screen. Traditional Braille is sufficient for note-taking (as it is possible with Braille laptops) but the character set of modern computers is based on seven bits or even eight bits, hence requiring more Braille characters. Most modern Braille displays make use of a technology for Braille with eight dots instead of six dots to extend the number of characters. Fig. 2 shows an example of eight dot Braille. Besides a standard for seven-bit ASCII, an industry standard exists for eight- dot American computer Braille. For European languages a similar industry standard exists which is based on code pages for the IBM PC. The main difference between computer-oriented Braille codes used in Europe and North America is the way digits are treated: the digit n in Europe is coded by the nth character of the alphabet with an additional dot 6 (for example, c = dots 1 and 4, 3 = dots 1,4 and 6) while in North America the nth character is shifted down one row in the matrix to represent digit n (c = dots 1 and 4, 3 = 2 and 5).
o. oo o. .. .o oo
.. o. .. .. o. .o
.. .. .. .. .o .o o. o. o. .. .. ..
Fig. 2: Sample text "ADA 94" in eight-dot Braille
The speed of experienced Braille readers (58 words per minute) is in some cases superior to readers using a CCTV (30 words per minute) (Denninghaus & Hupfield, 1987). Since Braille can be produced with only a stylus and a slate, its basic technology is cost effective and portable. A mechanical note-taker is much faster than writing on a slate, also portable, and very reliable. The use of transitory Braille displays connected to a computer is also suitable for communication with sighted readers.
Transitory Braille displays consist of a varying number of Braille modules. The number of modules built into commercial Braille displays is 20, 27, 40, 80 or 2x80. One manufacturer produces a Braille display with a vertical array of tactile pins in addition to the horizontal Braille modules. The exact number of Braille modules depends on issues such as portability, price, and the type of applications that are primarily used.
Technology for a single pin which is either set or reset can be electromagnetic or piezoelectric. The piezoceramic pins used in the Optacon are not used in transitory Braille displays as they are vibrating. An electromagnetic pin is in a casing (less than 3 mm in diameter) which contains a spring to set the pin (default) and a coil around a tiny rod of iron. If the iron is magnetized by the coil through induction, it pulls the pin (approximately 40 mm long) downwards. The pin is no longer raised.
A piezoelectric Braille display is a combination of a piezocrystal and a strip of metal (approximately 40 mm long, 2 mm wide, horizontal orientation). The piezocrystal reduces its length if a voltage of about 200 V is applied. As the metal does not change its length the stripe bends upwards and lifts a little pin. The force applied by the piezocrystal can reliably withstand the mass of the finger. When the voltage is stopped, the strip returns to its normal shape and the pin is no longer raised.
Because of the differences in orientation of the attenuators, piezocrystals cannot be built in arbitrarily large arrays. The only large tactile display--the pin-matrix device with 60 rows, each with 120 pins--is based on electromagnetic technology. The advantages of a piezocrystal are low power consumption and low noise emission, which make it the preferred technology.
Several approaches exist for virtual Braille displays. A virtual Braille display uses only one Braille module in combination with a pointing device. This can be a mouse with one Braille module built in (Braille Mouse). Another approach for a virtual Braille display is to put one Braille module into a little carriage that can be moved horizontally. Whenever a new position is reached it is detected by the computer and a new character is displayed. While cost effective, none of the currently tested virtual Braille displays has been suitable for the majority of Braille readers.
A transitory Braille display with 80 modules can display exactly one line of text shown on an Apple II computer, IBM PC or compatible. By using two extra-large keys, the reader can select other lines through going upwards or downwards. Reviewing does not interfere with an application program and is made easier through extra-keys to go to the top or bottom of the screen, to marked lines or to the cursor. The cursor is a unique character, usually marked by all dots raised. In some cases it is only marked by dots 7 and 8 to allow (partial) reading of the character below the cursor.
Whenever the cursor changes its position, the Braille display tracks it. Hence the position of the cursor changes, the line shown on the Braille display changes. Tracking the cursor is not easy in modern application programs because of the use of softcursors. A softcursor marks a particular spot by a unique character or a unique attribute (e.g., a highlighted word). The softcursor may be many characters wide (even covering many lines) and so the user must decide which end is to be followed.
Modern Braille displays have an extra input key or sensor (called the Braille or "routing" key) above the Braille pins. While working in a text editor the user starts reading the contents of the screen using the up/down keys. If he wants to change a particular word he has spotted, he should go back to where the cursor was and press arrow keys to bring the cursor to the desired spot. Using the Braille key, this task is much easier and faster. After pressing the Braille key, the Braille display automatically generates the right kind and number of arrow keys to make the cursor move to the Braille module being pointed at.
Tracking and routing are techniques that also apply to the mouse cursor whenever it is useful in DOS applications. Some new Braille displays are capable of replacing the use of a mouse with the use of the special Braille keys.
There are many different Braille applications and ways to use them. Adapting a Braille display to a particular non-standard application can be handled by experienced users through various input methods: a) through the use of function keys found on the Braille display while working with the application, b) through a separate application program which generates a file containing parameters, or c) through a combination where the user can write some parameters on the screen and tell the display to read them only from there. Nevertheless, the preferred input method is through parameter files being sent to the Braille display whenever a particular application is about to start and only occasionally changing the settings on the fly. As with screen-readers for speech output, there is no common way to adapt.
The first generation of Braille displays was used to convey less structured text, and were used for telephone operator displays, or for personal note-taking. The second generation of Braille displays was used to adapt existing devices such as terminals or typewriters. Only with the third generation, access to personal computers with random access to the screen and tracking of softcursors has become available. Finally, the fourth generation of Braille displays is also capable of cursor routing and has facilities for adaptation to non-standard application programs.
Braille displays can also be used in portable computers. Several new developments have been made to integrate 20 or 27 modules with a 486 notebook computer. Some even have Braille keys for routing input. Of course, review is more time-consuming as each line can only be read by three or four extra keystrokes, but the resulting portable devices can be operated approximately six hours without an external power supply.
The main difference between portable Braille computers and desktop systems stems from the lack of a hardware solution. Braille displays for desktop PCs can be built around an adapter card that implements tracking, review and routing independently of any operating system. Hence such a Braille display is also immediately suitable for a UNIX environment, during start-up of the PC (for instance to handle "setup"), or can run simultaneously with a speech-based screen-reader. Nevertheless, there are several Braille-based screen-readers for DOS that can interface through a serial or parallel port with a large or small Braille display.
Finally, Braille-based screen readers for access to graphical user interfaces (MS Windows) are now available or under development. We do not yet know if either Braille or speech is more suitable for access to GUIs, but a combination of both has been beneficial (Mynatt & Weber, 1994).
Braille is a different modality to get access to computers, compared to speech output. Braille is read by the fingers and is produced through mechanical typewriters or through a QWERTY keyboard using a PC. Each module of a transitory Braille display consists of six or eight pins. The technology that makes a little pin move upwards or downwards is either electromagnetic or based on a piezocrystal. Braille displays--like speech-based screen- readers--implement tracking of the cursor, reviewing the screen, and routing. Unlike speech output, the user can effectively and accurately recognize each character while reading, and he may point at it for routing. Four generations of Braille displays exist, each providing more features to work efficiently and accurately with standard application programs.
- Espinola, O.; Croft, D. _Solutions_. Boston: National Braille Press, 1992.
- Denninghaus, E. and Hupfeld, J. _Reading and Text Comprehension for Blind and Visually Impaired Students (in German), _Horus_ (2), 1987, pp. 50-56.
- Mynatt, E. and Weber, G. "Access to Nonvisual User Interfaces," in _Proceedings of CHI 94_. Addison Wesley, pp. 166-172.