We show that by analyzing the fingertip polygon area (which is an indication of the hand preshape) and the speed of hand movement (which is an indication of the hand transportation), we can divide a task into meaningful action segments such as approach object (which corresponds to the pregrasp phase), grasp object, manipulate object, place object, and depart (a special case of the pregrasp phase which signals the termination of the task). We introduce a measure called the volume sweep rate, which is the product of the fingertip polygon area and the hand speed. The profile of this measure is also used in the determination of the task breakpoints.
The temporal task segmentation process is important as it serves as a preprocessing step to the characterization of the task phases. Once the breakpoints have been identified, steps to recognize the grasp and extract the object motion can then be carried out.