Fitts' law and expanding targets: Experimental studies and designs for user interfaces

ABSTRACT

Recently, there has been renewed interest in techniques for facilitating the selection of user interface widgets or other on-screen targets with a pointing device. We report research into using target expansion for facilitating selection. Widgets that expand or grow in response to the user's focus of attention allow for a reduced initial size which can help optimize screen space use and may be easier to select than targets that do not expand. However, selection performance could plausibly suffer from a decreased initial widget size. We describe an experiment in which users select a single, isolated target button that expands just before it is selected. Our results show that users benefit from target expansion even if the target only begins expanding after 90% of the distance to the target has been travelled. Furthermore, our results suggest that, for sufficiently large ID values, users are able to take approximately full advantage of the expanded target size. For interfaces with multiple expanding widgets, however, subtle problems arise due to the collisions or overlap that may occur between adjacent expanding widgets. We give a detailed examination of the issues involved in both untiled and tiled multiple expanding targets and present various design strategies for improving their performance.

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INDEX TERMS

Primary Classification:
  H. Information Systems
  H.5 INFORMATION INTERFACES AND PRESENTATION (I.7)
      H.5.2 User Interfaces (D.2.2, H.1.2, I.3.6)
          Subjects: Graphical user interfaces (GUI)

Additional Classification:
  H. Information Systems
  H.1 MODELS AND PRINCIPLES
      H.1.2 User/Machine Systems
          Subjects: Human information processing; Human factors
  H.5 INFORMATION INTERFACES AND PRESENTATION (I.7)
      H.5.2 User Interfaces (D.2.2, H.1.2, I.3.6)
          Subjects: Theory and methods; Input devices and strategies (e.g., mouse, touchscreen); Interaction styles (e.g., commands, menus, forms, direct manipulation)

  I. Computing Methodologies
  I.3 COMPUTER GRAPHICS
      I.3.6 Methodology and Techniques
          Subjects: Interaction techniques

General Terms:
Design, Experimentation, Human Factors, Measurement, Theory

Keywords:
Empirical evaluation, Fitts' law, expanding targets, expansion, growing targets, interaction design, interaction modeling, target magnification, widget design