Extended Fitts’ Law for Dual Task: Pointing on IVIS during Simulated Driving

The purpose of this study is to identify a relationship between the time taken and the characteristics of touch key for touch-screen-based In-vehicle Information System (IVIS) and to suggest a new Fitts’ law formula that is added a driving speed parameter. Many studies already have shown that Fitts’ law is well fitted in various devices for primary tasks, but there is no study of Fitts’ law for secondary task in dual-task situation. However, task performer cannot fully pay attention to both the primary task and the secondary task, so the secondary task performance can be affected by the amount of attention for the primary task. Therefore Fitts’ law may not be applied for the secondary task. To verify this, we carried out an experiment that showed whether pointing task to touchscreen-based IVIS during driving is affected by driving speeds or not. In the experiment, 30 people were volunteered for participants and the participants carried out driving task and pointing on the screen of IVIS simultaneously. We measured the time to point a key on IVIS for every condition (3 driving speeds × 5 touch key sizes × 7 distances between steering wheel and touch key). As a result, there is an effect of driving speed on the pointing time. As we extended the index of difficulty of the conventional Fitts’ law formula by incorporating driving speed, we established an extended Fitts’ law formula for pointing on IVIS, which showed better accordance with dual task situation. This study can be evidence that secondary task performance is affected by degree of concentration on primary task, and the extended Fitts’ law formula can be useful to design interfaces of IVIS.