INTERFACE DESIGN SERVES to connect humans with technology (often computers). The human side of the equation provides the purpose, thought and intent, while the technology provides functionality.

Computers can easily do things that humans cannot do, or because of time constraints do not want to do. If the interface between the two is poorly designed or not "usable," the bridge between human and machine is weak and the task that the technology was meant to perform may not be accomplished.

In its simplest terms, user-centered design is described as "enhancing a system or product's 'usability' with measurable objectives such as speed of learning, reduction in error, task efficiency, and effectiveness in and reduction in need of support requirements" (McKnight, Dillon, & Richardson, 1996).

In the past two decades, technology of ever increasing functionality has come to pervade almost every aspect of human life. As the functionality of the technology increases, so does its complexity. User-centered design is an approach to design that serves to better meet the needs of a wide variety of end users for any number of potentially difficult tasks. This article explains three basic concepts central to the model of user-centered design and improved usability.

Users of a particular product vary immensely in their experience, skill, knowledge and intentions. Since technology has come to impact almost every aspect of human life in the 21st century, the range of user's potential skills, knowledge, habits and intentions are near infinite. In order to design a usable product, designers must first understand the end-user's skills, as well as their requirements for the task they intend to accomplish.

A mental model is an internal model that people form of themselves and of their world to provide predictive and explanatory power for understanding. 
 
Rollover the image to see how one product can accomplish entirely different purposes.

The tasks different users intend to complete with a product vary as much as the users themselves. One person's view of a product and the mental model that they attach to the product may vary drastically by the person's background, occupation, circumstances at the time of use (or environment) and experience with the product. It is therefore important to evaluate whether the design will allow the user to easily accomplish the task they intend to complete within the limits of their ability and environment.

Consider an ordinary tire, for example. We can safely assume that an auto mechanic and a young child view the utility of a tire in extremely different ways (see image above).

Once a designer has determined who the user is and what task they hope to accomplish, they may construct simple use-case scenarios that may be used as a reference throughout the design process. Use-cases are short statements, usually one to three sentences, that provide a simple context of use. Example use-case for remote control: "George is watching television and wants to change the channel putting forth as little effort as possible."

The information space is the collection of all documents, databases, instructional guides or reference material available to a user to aid them in the completion of their task. These are the resources they may turn to if they encounter an obstacle during their intended task. The information space of a commuter using a mobile phone while driving to work consists of the text on the screen and possibly an operator (assuming they are able to place a call). Once the commuter arrives at his/her destination, their information space immediately expands to include the phone's user guide, the manufacturer's web site, chat rooms as well as the resources they had access to while in the car. The focus of the information space should be a boundary, not the actual number of resources.

The points mentioned above combine to provide context to the designer's analysis. That is, the scenario in which the user, their task and the information space come together to create the user experience. The context of the use-case scenario (including the user, tasks and information space) or user experience should be at the center of effective design work. The context of a product’s use should be determined as early in the design process as possible. Since the context of the use-case is at the center of effective design, it is often referred to as the centrality of context.

Click on the arrow for a review of the principles discussed in this article.

Designers should practice user-centered design to make products that seems friendly, intuitive and above all, usable to the end-users.

Logical User-Centered Interaction Design

User-Centered Design: IBM

User-Centered Design for Hypertext

Don A. MacArthur
SDSU Educational Technology