Section: New Results

Perceived difficulty of pen gestures

Participants : Géry Casiez, Laurent Grisoni.

There are three primary factors which contribute to a successful gesture-based interface: the acquisition technology, the recognizer, and the design of the gesture set. Technologies to acquire gestures, and gesture recognition algorithms, are now quite robust and widely available. However, developing techniques and criteria to help designers create an intuitive and easy-to-perform gesture set remain an active area of research. The challenge is that in order to successfully integrate into an application, a gesture has to satisfy multiple criteria: it must be unambiguously recognized; fit well with its associated function; be easy to learn and recall; and be efficient to perform.

Our empirical results show that users perceive the execution difficulty of single stroke gestures consistently, and execution difficulty is highly correlated with gesture production time. We use these results to design two simple rules for estimating execution difficulty: establishing the relative ranking of difficulty among multiple gestures; and classifying a single gesture into five levels of difficulty. We confirm that the CLC model does not provide an accurate prediction of production time magnitude, and instead show that a reasonably accurate estimate can be calculated using only a few gesture execution samples from a few people. Using this estimated production time, our rules, on average, rank gesture difficulty with 90% accuracy and rate gesture difficulty with 75% accuracy. Designers can use our results to choose application gestures, and researchers can build on our analysis in other gesture domains and for modeling gesture performance [18] .