Improving the acquisition of small targets

This paper describes the design and comparative evaluation of three methods that aid the acquisition of small targets. The first method, called ‘bubble targets’, increases the effective width of the target as the pointer approaches. The second method uses a form of ‘stickyness’ to restrict movement as the pointer passes over an object. In the third method, called ‘goal-crossing’, the user simultaneously presses two mouse buttons before passing the pointer over the item. Goal-crossing overcomes the need for the user to decelerate the mouse when acquiring the target. Two evaluations were conducted, with the first (n=37) based on the acquisition of abstract targets for Fitts’ Law modelling, and the second based on an ecologically oriented window resizing task (n=11). Both showed that goal-crossing allowed the fastest target acquisition, but that it produced high error rates and was unpopular with participants. The ‘bubble’ and ‘sticky’ techniques also allowed faster target acquisition than the traditional approach, and users were enthusiastic about them. Fitts’ Law accurately modelled all techniques. Implications of the results for general user interface design are briefly discussed