Goal-directed aiming: Two components but multiple processes.

Abstract

This article reviews the behavioral literature on the control of goal-directed aiming and presents a multiple-process model of limb control. The model builds on recent variants of Woodworth's (1899) two-component model of speed-accuracy relations in voluntary movement and incorporates ideas about dynamic online limb control based on prior expectations about the efferent and afferent consequences of a planned movement. The model considers the relationship between movement speed and accuracy, and how performers adjust their trial-to-trial aiming behavior to find a safe, but fast, zone for movement execution. The model also outlines how the energy and safety costs associated with different movement outcomes contribute to movement planning processes and the control of aiming trajectories. Our theoretical position highlights the importance of advance knowledge about the sensory information that will be available for online control and the need to develop a robust internal representation of expected sensory consequences. We outline how early practice contributes to optimizing strategic planning to avoid worst-case outcomes associated with inherent neural-motor variability. Our model considers the role of both motor development and motor learning in refining feed-forward and online control. The model reconciles procedural and representational accounts of the specificity-of-learning phenomenon. Finally, we examine the breakdown of perceptual-motor precision in several special populations (i.e., Down syndrome, Williams syndrome, autism spectrum disorder, normal aging) within the framework of a multiple-process approach to goal-directed aiming.

Manual aiming in healthy aging: does proprioceptive acuity make the difference?

“…Referring to the multiple processes model (Elliott et al 2010), the play-it-safe strategy could be implemented by formation of internal representations of longer movement time, shorter movement displacements, and lower movement speed during both movement initiation and homing-in phase. The fact that increased movement time and homing-in durations were accompanied by increased number of corrective submovements in all four groups suggests that the play-it-safe strategy was adopted as a default strategy when visual feedback was withdrawn.…”

“…According to the multiple-process model of limb control (Elliott et al 2010), manual aiming movements generally consist of two consecutive phases: a primary movement and a homing-in phase. The primary movement corresponds to the initial pulse toward the vicinity of target.…”

“…While corrections may occur very early in the movement, the main body of closed-loop control takes place during the homing-in phase. Herein, visual and proprioceptive feedback is used in the final movement phase to correct for any spatial discrepancy between hand and target positions (i.e., limb-target control; see Elliott et al 2010). This final movement phase (homing-in) is characterized by one or more corrective submovements that guide the hand to the target's position.…”

The relative timing between eye and hand in rapid sequential pointing is affected by time pressure, but not by advance knowledge

“…Abrams et al 1990;Binsted et al 2001), thus indicating that the hand movement is planned and initiated on the basis of peripheral visual information, in conjunction with feedforward information from ocular motor command (Desmurget and Grafton 2000; Prablanc et al 1979a, b). Then, contrary to single-target aiming tasks, where foveal visual feedback plays an important role in the latter phase of the movement as the hand approaches the target (for a review, see Elliott et al 2010), in sequential aiming or object manipulation tasks, gaze is often found to shift to the next point of interest before the preceding hand movement has been completed (e.g. Helsen et al 2004;Johansson et al 2001).…”

“…According to Neggers and Bekkering, this 'gaze anchoring strategy', characterized by the inhibition of a saccadic shift during an ongoing hand movement, facilitates online control using foveal vision of the hand as it approaches the target (Elliott et al 2010). However, rather than being in direct opposition, it is possible that 'gaze anchoring' Bekkering 2000, 2001) and 'buffering' (Wilmut et al 2006) reflect two modes of the visuo-motor system, which operate under different task constraints.…”