Two-phase strategy of neural control for planar reaching movements: I. XY coordination variability and its relation to end-point variability

Abstract

A quantitative model of optimal transport-aperture coordination (TAC) during reach-to-grasp movements has been developed in our previous studies. The utilization of that model for data analysis allowed, for the first time, to examine the phase dependence of the precision demand specified by the CNS for neurocomputational information processing during an ongoing movement. It was shown that the CNS utilizes a two-phase strategy for movement control. That strategy consists of reducing the precision demand for neural computations during the initial phase, which decreases the cost of information processing at the expense of lower extent of control optimality. To successfully grasp the target object, the CNS increases precision demand during the final phase, resulting in higher extent of control optimality. In the present study, we generalized the model of optimal TAC to a model of optimal coordination between X and Y components of point-to-point planar movements (XYC). We investigated whether the CNS uses the two-phase control strategy for controlling those movements, and how the strategy parameters depend on the prescribed movement speed, movement amplitude and the size of the target area. The results indeed revealed a substantial similarity between the CNS's regulation of TAC and XYC. First, the variability of XYC within individual trials was minimal, meaning that execution noise during the movement was insignificant. Second, the inter-trial variability of XYC was considerable during the majority of the movement time, meaning that the precision demand for information processing was lowered, which is characteristic for the initial phase. That variability significantly decreased, indicating higher extent of control optimality, during the shorter final movement phase. The final phase was the longest (shortest) under the most (least) challenging combination of speed and accuracy requirements, fully consistent with the concept of the two-phase control strategy. This paper further discussed the relationship between motor variability and XYC variability.

Eye-Hand Coordination during Visuomotor Adaptation with Different Rotation Angles

“…For the analysis of initial direction errors, a reference line was defined as the line connecting the hand position at movement onset and the center of the target (in the case of baseline condition) or the hand position that would place the cursor on the target center under the rotated feedback (in the case of practice condition). The initial direction was computed as the angular deviation from the reference line to the line connecting the hand positions at movement onset and at 10 mm distance point from the onset (see the use of a similar procedure [53] ). The initial direction was positive (or negative) when a hand-path was directed CCW (or CW) to the reference line.…”

Velocity neurons improve performance more than goal or position neurons do in a simulated closed-loop BCI arm-reaching task

“…The MSC (Liao and Kirsch, 2014 ) is based on the hypothesis that target-oriented arm reaching movements consist of a series of overlapping submovements (Lee et al, 1997 ; Burdet and Milner, 1998 ; Rohrer et al, 2004 ; Fishbach et al, 2007 ) that each represent corrections to the movement based on feedback AND whose summation represents the commanded trajectory. Under this hypothesis, the early portion of each reach is not specified precisely (Rand and Shimansky, 2013 ) and tends to undershoot the target (Worringham, 1991 ), necessitating corrections in order to achieve the target. Thus, the intended goal does not necessarily coincide with the target early in the reaching movement (Lyons et al, 2006 ).…”

Characterizing and Predicting Submovements during Human Three-Dimensional Arm Reaches

“…We assumed this model of error corrections based on literature, and used it to build a model capable of making error corrections during simulated arm reaches. Approaches that are not based on submovements, such as the two-phase strategy of Rand & Shimansky [43], [52], could also work and deserve further investigation.…”