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4.2. ROLE OF PROTOTYPES IN THE FORMAL DESIGN STAGE

Prototypes are the first concrete embodiment of the user interface design. They allow users to experience something resembling a real product and thus provide more useful critical feedback. For the design team, building a prototype immediately highlights some of the erroneous design assumptions that may have been carried over from the Exploratory and Refinement and Analysis Stages.

A series of low-fidelity, paper-based prototypes are used primarily in the early stages of the user interface design process to map out both the dialogue design and the detail design. High-fidelity, computer-based techniques are the principal tools used in refining the exact interaction and graphic details. Both types of prototype can be subjected to usability testing.

Although prototyping is a very powerful design tool, as with iterative design it should not be an excuse for not doing a thorough-enough user analysis. The limitations of the prototyping tools can begin to negatively influence both the design team and the users (e.g., some tools make it difficult to create anything other than a standard Windows interface). Finally, prototypes, particularly high-fidelity simulations, can give the design team as well as managers and clients the impression that a project is much closer to completion than it actually is.

4.2.1. Low-Fidelity Paper Prototypes

Paper prototypes are very useful to try out a variety of dialogue concepts inexpensively in a short period of time. Paper prototyping allows for early user feedback and rapid iteration of the concrete user interface design.

In building paper prototypes only key states of the user interface are initially depicted and tested. This ensures that the high-level work flow and navigation issues are addressed and that basic usability requirements are met before the designer is caught up in design details. As the design is further refined, virtually all states can be drawn. This makes it easy to get the “big picture” of how a particular task would be supported, simply by laying out the entire sequence of drawings on a large table.

In the Orbitor project, paper prototyping resulted in a detailed depiction of most of the important states of the user interface (see Figure 11.5). These were hand-drawn sketches of what the user interface would look like at full 1:1 scale. This full-scale paper prototyping was useful to keep the design team conscious of critical ergonomic issues (text legibility, size of icons and touch targets) associated with a small display interface.


Figure 11.5  Paper prototype.

Informal usability testing was conducted with local users (often fellow employees) on an ongoing basis. This was a way of receiving fast and inexpensive feedback to support the ongoing iterative design process. Overall scenario-storyboarding and paper prototyping were the most useful and widely used techniques for- rapid design of new generation products such as Orbitor.

4.2.2. High-Fidelity Interactive Simulations

As the design team begins to focus on the optimized and preferred user interface, the paper prototypes are transferred to an interactive computer simulation. Some of these simulation applications include MacroMedia Director, Super Card, and Visual Basic. A high-fidelity interactive simulation is used to integrate all of the disparate elements of the paper prototype. During the transition stage between paper and a computer simulation, it is fastest to revisit problem areas of the user interface simulation and first refine them using paper prototyping. This takes advantage of the speed of paper, while capturing only the output in a more finished interactive computer simulation. Interactive simulations are used to develop and refine the interaction sequences, interaction timing, graphics design details, and animation sequences. The interactive simulation gives the design team a feel for the real-time flow of the interaction dialogue (see Figure 11.6).


Figure 11.6  High-fidelity interactive simulation of multitasking (simultaneous voice call and note).

An interactive simulation is further used for formal usability testing with end users. The information received from usability test sessions is a key element in the design decision process, and ongoing usability feedback is required for efficient iterative design. The subject of detailed usability testing is outside the focus of this chapter (see Neilsen, 1993; Wiklund, 1994; Bauersfeld, 1994; Hix et al, 1993).

In the Orbitor project, seven formal usability test sessions were conducted with over 50 subjects in total, to refine the various elements of the interface. The interactive and realistic nature of the simulation served to convincingly demonstrate the strengths and weaknesses of the Orbitor interface as it evolved. The implications of new developments in the simulation could be quickly grasped both by users who had seen previous iterations and those encountering the simulation for the first time. The simulation also proved an effective tool for communicating the intricacies of the user interface to managers, partners, and potential customers.

4.3. THE CONCEPTUAL MODEL

The terms conceptual model, mental model, and metaphor have been defined quite differently by various designers (see Norman, 1988; Laurel, 1990; Bauersfeld, 1994; Zetie, 1995). While many of these designers use users’ conceptual model and users’ mental model interchangeably, Collins (1995) states that, “conceptual models are externalized representations of mental models, in words or pictures, that can be shared. The users’ conceptual model represents the users’ understanding of their task. It includes goals for using the system and knowledge of how the capabilities of the computer system relate to the objects and processes of the real-world domain.” This chapter will follow Collins’ definition of conceptual model.

The development of a conceptual model is central to the success (and usability) of a new-generation interface. A users’ conceptual model should be explicitly designed into the interface by the design team. From the user feedback to concepts developed in the two earlier stages, the design team should have insight into what attributes contribute to a workable conceptual model. However, this model will often evolve through usability testing and iterative design in the Formal Design Stage. The conceptual model provides a guiding framework for a design team in the refinement of an interface, and it also guides users through the interface by allowing the user to systematically discover the various functions of an application. The conceptual model is communicated both through the flow of the dialogue in an interface as well as the use of metaphors.


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