Crossing-based selection with direct touch input

Fundamental performance results for crossing-based selec-tion tasks with direct touch input are presented. A close adaptation of Accot and Zhai's indirect stylus crossing ex-periment reveals similar trends for direct touch input: touch crossing task time is faster or equivalent to touch pointing; continuous selection of large orthogonal crossing targets is most effective; and continuous selection of small collinear targets is least effective. Unlike indirect stylus and mouse crossing, not every kind of direct touch pointing perfor-mance is modeled accurately with standard Fitts' law. Instead, Fitts' law, used previously for touch pointing with small targets, is used to more accurately model discrete touch crossing with a directionally constrained target. In addition, visual touch feedback is shown to have a strong effect on absolute accuracy. Our work empirically validates touch crossing as a practical and efficient selection technique, and motivates the exploration of novel forms of expressive multi-touch crossing.