The presence of a visual target range before and during movement causes a violation of Fitts' Law


Fitts' Law predicts that a target which is farther away and/or smaller than another will take more time to reach. However, if potential target locations are individually outlined before and during a movement, movement time (MT) to the farthest target is faster than predicted (i.e., Fitts' Law is violated). One hypothesis proposes that a gestalt (an object made of discrete parts) is created by the performer's perception of the outlined targets, and, because the edges of a gestalt are processed faster than the middle, MT to the farthest target is faster than expected. The goal was to test this hypothesis by determining if Fitts' Law is violated when the range in which a target will appear is outlined prior to and during target presentation, emulating a gestalt. Participants (N=22; 26.3±4.0 years old; 13 cis-female, 9 cis-male) started with their right index finger on a home position while a target range was outlined to the right. Following a randomized foreperiod , a target appeared within the range, to which participants pointed 'as quickly and as accurately as possible.' Across 180 trials, movements were measured with the touchscreen. MT to the middle (371.9±93.2ms) and far (375.2±97.6ms) targets were not different (p=0.575), while MTs to both the middle and far targets were slower than MTs to the nearest targets (360.7±94.7ms; both p<0.001). Like when individual targets are outlined before and during movement, a violation of Fitts' Law occurred when participants were presented with an outline around a potential target range, corroborating the gestalt hypothesis.