Control Strategy in Movements with Transmission Delay

The strategy used by participants was studied when making movements in a Fitts movement paradigm with transmission delay between control input and display output. Fitts' law in the modified form developed by E. R. Hoffmann (1992) gave an excellent description of the data. Movement time could also be expressed as a function of the total delay time (number of submovements × transmission delay) and Fitts' index of difficulty (ID). Two types of submovement were identified, being step and drag forms. The number of step submovements was the most important in determining movement time. These were related to a move-and-wait strategy used by participants. Number of submovements increased with the level of ID and transmission delay and was linearly related to the ID and product of ID by transmission delay.