Interaction Devices

Interaction devices is a term used to cover the various devices used to interact with a computer. Most are familiar to you so the comments hare are brief.

Keyboards and Function Keys

The main observation to make here is that the familiar QWERTįkeyboard design was originally intented to slow down the rate at which people typed to allow for the mechanics of typewriters. The Dvorak keyboard allows much faster entry but has never caught on.

"Chording" on a keyboard with fewer keys can also be effective. Chording means that several keys are actuated at once to enter a symbol. Court reporters achieve 300 wpm on chording devices. (If you have seen a good pianist you will realise what might be accomplished).

Cursor movement keys should be arranged in a way that refelects their effect on the cursor. This applies just as much when the keys are embedded in the alphabetic keys.

When special keys like ALT, ESC and CTRL are used to change the meaning of the another key care should be taken to choose (and share with the user) a consistent set of choices for the effects.

Pointing Devices

Pointing devices are applicalbe in the following six types of tasks.

  1. Selecting an item;
  2. Positioning;
  3. Orienting: Eg choosing a direction in two or three dimensional space
  4. Path: The result of a sequnce of positioning and orientation choices can be used to draw a path;
  5. Quantifying: A one dimensional choice of a number to set a parameter.
  6. Text: Locating blocks of text in a two dimensional document, for insertion movement or deletion.

Pointing devices include direct devices such as lightpens and touch screens and indirect ones such as mice, moles, and bats. It is possilbe to model the time that it takes for a user to move a givne distance D to a target of width W using Fitt's law. The index of difficulty is given as

          log  (2D/W)
More perspicuous estimates have been made. For details see section 6.3.2 of the book by Schneiderman.

Speech Recognition and Digitization

Speech recognition has been used in cases where it is necessary for the user to have both hands free and for the handicapped. To date it requires that the system be trained to recognize the user's voice, which may of course change when the user has a cold. Furthermore the system works best when the words are enunciated separately rather than continuously as in normal speech. In general as with most AI type applications it works best when the domain of discousre is suitably restricted. Speech generation on the other hand is much easier and can be used quite effectively.


For many tasks monochrome displays are quite adequate, especially when they have high resolution. ( I prefer my greyscale SUN to my color PC at home). Color displays do offer more opportunities for multimedia, as well as for clutter.

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Last Changed 10 April 1995