Abstract
Fitts's Law (1954) states that the time required to complete a pointing movement (MT) is dependent on the index of difficulty (ID) of the target, which is calculated using movement amplitude and target width. However, Heath et al. (2011) reported that the influence of amplitude and width on MT/ID slopes differ significantly, which challenges Fitts's Law. While early research on Fitts's Law (e.g., Fitts and Peterson, 1964) included terminal feedback of endpoint accuracy, more recent research has not. The current study aimed to reproduce the results of Heath et al. (2011) and also assess the influence of terminal feedback on the MT/ID slopes for amplitude and width manipulations. In two separate sessions, participants made fast and accurate discrete pointing movements to one of sixteen targets (4 amplitudes; 4 widths) with ID's ranging from 2.63 to 5.25. In one of the sessions, participants were given visual terminal feedback regarding endpoint accuracy following the completion of each trial (undershoot, accurate, overshoot). As in Heath et al. (2011), the influence of amplitude on MTs was significantly greater than the influence of target width. However, when using the effective target width to calculate the effective ID (IDe), the MT/IDe slopes associated with amplitude no longer differed from the MT/IDe slopes associated with target width. In addition, participants differed in their use of terminal feedback.Acknowledgments: This research was supported by the Natural Sciences and Engineering Research Council (NSERC), the Canada Foundation for Innovation (CFI) and the Ontario Research Fund (ORF).