The violation of Fitts' Law: an examination of displacement biases and corrective submovements

Roberts, James W. and Blinch, Jarrod and Elliott, Digby and Chua, Romeo and Lyons, James L. and Welsh, Timothy N. (2016) The violation of Fitts' Law: an examination of displacement biases and corrective submovements. Experimental Brain Research, 234 (8). pp. 2151-2163. ISSN Print ISSN 0014-4819 Online ISSN 1432-1106

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Fitts’ Law holds that, to maintain accuracy, movement times of aiming movements must change as a result of varying degrees of movement difficulty. Recent evidence has emerged that aiming to a target located last in an array of placeholders results in a shorter movement time than would be expected by the Fitts’ equation – a violation of Fitts’ Law. It has been suggested that the violation emerges because the performer adopts an optimized movement strategy in which they partially pre-plan an action to the closest placeholder (undershoot the last placeholder) and rely on a secondary acceleration to propel the limb toward the last location when it is selected as the target (Glazebrook et al., Hum Mov Sci, 39:163-176, 2015). In the current study, we examine this proposal and further elucidate the processes underlying the violation by examining limb displacement and corrective submovements that occur when performers aim to different target locations. For our Main Study, participants executed discrete aiming movements in a five-placeholder array. We also reanalysed data from a previously reported study in which participants aimed in placeholder and no placeholder conditions (Blinch et al., Exp Brain Res, 223: 505-515, 2012). The results showed the violation of Fitts’ Law unfolded following peak velocity (online control). Further, the analysis showed that movements to the last target tended to overshoot and had a higher proportion of secondary submovements featuring a reversal than other categories of submovement (secondary accelerations, discontinuities). These findings indicate that the violation of Fitts’ Law may, in fact, result from a strategic bias towards planning farther initial displacements of the limb which accommodates a shorter time in online control.

Item Type: Article
Keywords: Fitts’ Law, movement optimization, reversal submovements, pre-planning, online control
Faculty / Department: Faculty of Science > School of Health Sciences
Depositing User: James Roberts
Date Deposited: 06 Mar 2017 12:45
Last Modified: 20 Jul 2018 10:45

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