Capture of shrinking targets with realistic shrink patterns

Abstract

Previous research [Hoffmann, E. R. 2011. “Capture of Shrinking Targets.” Ergonomics 54 (6): 519–530] reported experiments for capture of shrinking targets where the target decreased in size at a uniform rate. This work extended this research for targets having a shrink-size versus time pattern that of an aircraft receding from an observer. In Experiment 1, the time to capture the target in this case was well correlated in terms of Fitts' index of difficulty, measured at the time of capture of the target, a result that is in agreement with the ‘balanced’ model of Johnson and Hart [Johnson, W. W., and Hart, S. G. 1987. “Step Tracking Shrinking Targets.” Proceedings of the human factors society 31st annual meeting, New York City, October 1987, 248–252]. Experiment 2 measured the probability of target capture for varying initial target sizes and target shrink rates constant, defined as the time for the target to shrink to half its initial size. Data of shrink time constant for 50% probability of capture were related to initial target size but did not greatly affect target capture as the rate of target shrinking decreased rapidly with time.

Abstract

Practitioner Summary: Shrinking targets occur in applications such as gunnery, computer games and game shooting, where the object to be shot or captured moves away from an observer. Times for capture of shrinking targets are developed in terms of a modified form of Fitts' law.

Keywords::

• Fitts' law
• shrinking targets
• movement time

Acknowledgement

The work described in this paper was fully supported by a grant from the City University of Hong Kong (Project number 7002820).