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Human Performance at the Computer – Part 1: Introduction

By Gerd Waloszek, SAP User Experience, SAP AG – October 4, 2008

In previous articles, I have discussed human performance at the computer and distinguished between three aspects of performance: system performance, system responsiveness, and human performance (see, for example, The Three Pillars of Human Performance at the Computer – Which One Fits Best?). I pointed out that in order to improve the overall performance of the human-computer system, all three aspects need to be optimized. In this series of four articles I want to pick up the topic of human performance at the computer, include new insights, and discuss performance-related issues that can be approached by UI designers. I will also devote an article to the concept of perceived performance.

 

Overview of the Aspects of Human Performance at the Computer

In figure 1 below, I provide a schematic overview of the three above-mentioned performance aspects, the primary questions that are involved, and how these aspects are related to technology and UI design:

The Aspects and the Related Questions

  • System performance relates to the question: "How fast is the computer?"
    Optimizing system performance includes all involved technical components, such as the processing, the network, and the visual rendering. Speed is the motto, here, and we are in a purely technical domain. Increasing speed reduces waiting times, and it is hoped that with sufficient speed these can be reduced to practically zero.
  • Human performance relates to the question: "How can we improve human performance through UI design?"
    It points to the fact that user interface design plays a critical role for the performance of human users and attempts to design software applications in ways that the users' performance is optimized. Here, we are primarily in the UI design domain, including interaction, information, and visual design, although technical considerations also have to be considered.
  • System responsiveness relates to the question: "How long do users have to wait at the computer?"
    When attempting to improve the system's responsiveness, developers and UI designers strive to reduce the users' waiting times in spite of the fact that some system processes – for example, the ones that the users just had started – have not finished yet. That sounds like a paradox and you can imagine that some creativity is needed to come up with good solutions here. The question above sounds as if we were in a purely technical domain, but this is not the case, as waiting times have an impact on users. Therefore, this aspect requires close cooperation between technology and UI design, and thus figure 1 puts it in both fields.
  • Finally, there is the term perceived performance, which relates to the question: "How do users perceive the system's and their performance?"
    It indicates that there is often a difference between objective performance and the subjective impression that it makes on the users. It is not included in figure 1.

Overview of system performance, system responsiveness, and human performance and the related questions

Figure 1: Overview of system performance, system responsiveness, and human performance and the related questions

For a more detailed discussion of the differences between the three above-mentioned aspects, see also my article The Three Pillars of Human Performance at the Computer – Which One Fits Best?

 

A General Strategy for Improving the Performance of the Human-Computer System

Having put together the different aspects of human performance at the computer and the questions that arise in this context, we can define a simple overall strategy for improving the performance of the human-computer system. Figure 2 presents the strategy as a diagram:

Overview of a general strategy to improve the performance of the man-computer system

Figure 2: Overview of a general strategy to improve the performance of the man-computer system

In figure 2, I integrated performance aspects and related questions into a strategy that focuses on four aspects, only three of which are within the scope of UI designers:

  1. First of all, the system performance aspect needs to be attacked, because a satisfying system performance is the prerequisite for all other work. While this is an important step, it typically meets technical limits because not all waiting times can be reduced to practically zero. Despite all technical progress – note that computers have become more than a thousand times faster in the last 25 years – users still have to wait at the computer and often even more and longer than they did ten or twenty years ago.
  2. Secondly, system responsiveness needs to be attacked if the system's performance cannot be improved sufficiently. I noted already that waiting times have a psychological aspect. Viewing waiting times from a user's perspective helps UI designers guide development and give advice on which aspects need further improvement and which are already good enough that it would be a waste of resources to continue work there.
  3. Improving perceived performance is closely related to improving responsiveness, particularly to the question of what can be done if waiting times cannot be further reduced. It has been shown that different forms of feedback increase the users' tolerance for waiting times.
  4. Last but not least, improving the users' efficiency is one more area, where the performance of the human-computer system can be optimized. It turns out that times can be much larger in this area than in the technical ones. I indicated already that this aspect is connected to various aspects of user interface design: interaction design, information design, and visual design.

 

Outlook: Possible Directions and How this Article Series Continues...

Finally, I would like to extend figure 1 to indicate the directions in which the strategy described above might proceed:

Extension of figure 1 to indicate the directions in which the strategy might proceed

Figure 3: Extension of figure 1 to indicate the directions in which the strategy might proceed

In the responsiveness area, we see that UI designers can come up with evaluations of waiting times that are based on the users' perception and reactions. Based on knowledge about users they can also give recommendations to the development and technical teams. The aspect of human performance is approached through the various facets of UI design and bears the danger of becoming huge and encompassing the whole UI design field. Performance-oriented guidelines can be a way to avoid this trap and to stay focused on performance-related UI design aspects.

To discuss some of the directions indicated in figure 3, this introductory article is accompanied by three further articles, which cover the following aspects:

We shall see that responsiveness and perceived performance methods are often closely related and difficult to keep apart. Nevertheless, these aspects are discussed in separate articles. Improving system performance, on the other hand, is beyond the scope of user interface designers and will therefore not be further discussed in this article series. Also note that the aspect of feedback in the event of delays (item 3 in the strategy) is covered in a separate series of articles (Waiting at the Computer: Busy Indicators and System Feedback).

 

References

 

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