HCI Standards: Bases and Examples

by Elizabeth Buie (copyright notice)

This page provides some examples of HCI design recommendations that often appear in standards and that are based on human physical, cognitive, and affective characteristics.

Physical factors

Some of the recommendations in standards for software HCI are based on the physical attributes of human beings. (Hardware standards, on the other hand — screen reflectivity, for example, or the force required to press a key or mouse button — have a much stronger physical basis. This discussion addresses only software HCI.)

Here are two examples of physically based HCI recommendations:

• Saturated red text
  on a saturated blue
  background — a no-no
  Avoid displaying saturated red text on a saturated blue background (or vice versa). A condition called "chromostereopsis" makes the text extremely difficult to read for most people (example at right). The eye, you see, focuses different wavelengths of light (i.e., colors, whence "chromo") differently. (So does a camera's lens, for that matter, and in fact a few "apochromatic" lenses are designed to counteract this.) Anyway, when red is in focus, blue appears ever-so-slightly fuzzy, and vice versa. This makes red and blue seem to be at different distances (whence "stereo") from the viewer's eye (whence "opsis"). (Note: Green is almost as bad as blue.)
• Use motion only for getting and keeping the user's attention. Peripheral vision is more sensitive to motion (e.g., animation and blinking) than is foveal vision -- i.e., movement that you see out of the corner of your eye will tend to distract you from anything else on the screen. (I'm not showing an example of this because I want you to read this page. But just look at any web page with an animated ad banner, and notice how hard it is to keep your eyes on the page content. And you know they want your attention!)

Physically based recommendations tend to be stronger advice than cognitively or affectively based ones because the relevant characteristics vary less from person to person. You and I may have rather different likes or learning styles (you may even be a Windows fan, heaven help us!), but virtually everyone with normal color vision experiences chromostereopsis in looking at red on blue.

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Cognitive factors

There are so many recommendations based on cognitive factors that I had trouble deciding which ones to choose. Anyway, here are two:

• When listing options for user selection (e.g., in a menu or list box), present them in an order that makes sense to the user's task, grouping them if there are more than just a few. If there is no logical order, list the options alphabetically. For example, a File menu has New and Open together, Page Setup and Print together, and Quit at the bottom (except in Claris Home Page, which lists the ten most recently used files at the bottom, below Quit), while a font list shows the available fonts in alphabetical order by name. This recommendation takes advantage of the user's understanding of the task or of some other organizing principle and facilitates finding items in the list.
• Provide keyboard mechanisms ("shortcuts" or "accelerators") for commonly used functions and menu items. This allows users who become familiar with the product to use the keyboard for what may be faster access to those functions.

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Affective factors

Affect (pronounced af'fect) is, essentially, subjective reaction. It includes emotions, values, preferences, satisfaction — all the stuff it's so hard for many of us to get a handle on. But if we want our users to be satisfied with our products, we have to pay attention to it. Here are two examples of recommendations based on considerations of user affect:

• Design to put users in control of the interaction. For example avoid giving the impression that the computer is telling them what to do, and do not use loaded words such as "illegal" in error messages. (Nobody is going to jail for spelling a command name wrong.)
• Provide for some user customization of the æsthetics of the interface. Examples include Macintosh Appearance controls, Windows Schemes, and Motif Palettes.

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This article was published in the March/April 1999 issue of interactions, the bimonthly magazine of ACM/SIGCHI. Copyright © 1997, 1998, Elizabeth Buie. All rights reserved. Permission is granted to print this page or link to it, as long as such use is personal or educational and is not for commercial gain or profit. This article may not be republished or redistributed without permission.
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