Precision Constraints during Pointing with a Stylus: Implications for Fitts’ Law

Abstract

Previous research on performance on the Fitts pointing task has identified the relative influences of task and effector constraints. Effector constraints are those specific to the motor and physical aspects of the task, such as movement distance, which tend to affect the overall duration of the movement. Task constraints, such as target size, affect the underlying movement dynamic, with effects isolated to the end of the movement, causing asymmetry in the velocity profile. Here, evidence confirming these effects is reported, along with a new task constraint, target size as defined as a physical constraint on final positioning error. A new formulation of Fitts’ law is presented that accounts for all constraints.