Tovi Grossman, Ravin Balakrishnan Dep. of Computer Science Univ. of Toronto CHI 2004

Introduction Background Goals and Directions of the Current Study Experiment Implications for User Interface Design Conclusion

Advances in three dimensional display technology Appropriate user interfaces : easily select and manipulate virtual elements in the 3D display space. They studied and modeled user performance in the most fundamental interaction task – pointing – in a 3D display. Contents of paper  review previous work on pointing and Fitts’ law models in 1D and 2D  identify various factors and interactions between them in 3D pointing  propose several mathematical models  controlled experiment  Implications for user interface design

Fitts’ law  One dimension  Two dimension (Mackenzie and Buxton, 1992)  Accot and Zhai (2003) : A weighted Euclidean model  Ware et al. (1994, 1997) : 3D model, similar to 2D model A W A W H

Experimental Hardware Platform : volumetric display was used Manipulation of Experimental Parameters  Target dimension : W, H, D  Movement angle : Ө  uses a approach angle of 0° Modeling  First baseline model & Weighted model  Weighted Euclidian model  Incorporating f( Ө ) into the ID Wtmin model  Incorporating f( Ө ) into the ID WtEuc model

Apparatus Participants  5 female and 7 male, ages from 20 to 25 Procedure : cuboids target, XZ plane, 3D cursor Design  A(3) Ⅹ H(4) Ⅹ W(4) Ⅹ D(4) Ⅹ angle(3) = 576 combinations, 3 sessions, random order  6 reciprocal movements, 2 practices, 6 groups, 1 hour per each session Performance measure  Movement time, number of errors per trial

Movement time analysis  Main effect : all had a main effect on MT (angle : 0, 45, 90)  Effect of movement direction : no effect  Interactions (Ө ↔ W, D, H) : no H Ⅹ θ → targets were located in the XZ plane  Relative effect of target dimensions : Figure 4e  Interactions betw. target dimensions : Figure 5

Movement time analysis  Main effect : all had a main effect on MT (angle : 0, 45, 90)  Effect of movement direction : no effect  Interactions (Ө, W, D, H) : no H Ⅹ θ  Relative effect of target dimensions  Interactions betw. target dimensions

Movement time analysis  Fit of the models Error analysis : effects for D,H,W, no effect for A, error rate 15.7%, 0.04 units → error ↑ “racing through the experiment”

Target sizing  target size → error rate  dimension parallel to the line of approach Target positioning  moving forward and backward → left and right  adjust the layout of the interface elements according to the position of users

A true 3D volumetric display Moving forwards and backwards in depth is slower than moving left and right for selecting targets. The target width was more critical than the height and depth of the target. The effect of the height was constant regardless of the movement angle. Accounts for varying movement angles The implications of our results for the sizing and positioning of user interface widgets in 3D displays

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