Mechanisms underlying the generation of averaged modified trajectories

Abstract

Abstract. In this work we have studied what mechanisms might possibly underlie arm trajectory modification when reaching toward visual targets. The double-step target displacement paradigm was used with inter-stimulus intervals (ISis) in the range of 10-300 ms. For short ISis, a high percentage of the movements were found to be initially directed in between the first and second target locations (averaged trajectories). The initial direction of motion was found to depend on the target configuration, and on D: the time difference between the presentation of the second stimulus and movement onset. To account for the kinematic features of the averaged trajectories two modification schemes were compared: the superposition scheme and the abort-replan scheme. According to the superposition scheme, the modified trajectories result from the vectorial addition of two elemental motions: one for moving between the initial hand position and an intermediate location, and a second one for moving between that intermediate location and the final target. According to the abort-replan scheme, the initial plan for moving toward the intermediate location is aborted and smoothly replaced by a new plan for moving from the hand position at the time the trajectory is modified to the final target location. In both tested schemes we hypothesized that due to the quick displacement of the stimulus, the internally specified intermediate goal might be influenced by both stimuli and may be different from the location of the first stimulus. It was found that the statistically most successful model in accounting for the measured data is based on the superposition scheme. It is suggested that superposition of simple independent elemental motions might be a general principle for the generation of modified motions, which allows for efficient, parallel planning. For increasing values of D the inferred locations of the intermediate targets were found to gradually shift from the first toward the second target locations along a path that curved toward the initial hand position. These inferred locations show a strong resemblance to the intermediate locations of saccades generated in a similar double-step paradigm. These similarities in the specification

Reaching Within a Dynamic Virtual Environment

“…In addition, mean duration of paused movement was significantly shorter in Experiment 1 than Experiment 2 (117 vs. 156 ms; χ 2 (1) = 5.57, p = 0.018). Although the proportion of paused movements was similar with both scene conditions in both experiments, the duration of the pause was significantly different between the scene that was matched to head motion (120 ms) and the rolling scene (190 ms) in Experiment 2 (χ 2 (1) = 15.8, p < 0.0001). Furthermore, the 3D hand path was consistently curved for both single-and double-step conditions, irrespective of target position and scene condition.…”

“…Studies have shown that both young and elderly healthy subjects are able to amend their ongoing movements in response to target displacement during a "double-step" paradigm which changes the spatial goal of the movement by unexpectedly changing the location of a visual target [1][2][3][4]. However, these movements have only been tested in stationary visual environments.…”

A computational analysis of motor synergies by dynamic response decomposition

“…This strategy would be in line with the hypothesis of an intermittent controller that sequentially initiates discrete movement primitives (Fishbach et al, 2005; Loram et al, 2010; Squeri et al, 2010; Karniel, 2013). Submovements might be combined in time succession (Soechting and Terzuolo, 1987; Meyer et al, 1988), or based on the vectorial summation of overlapping preplanned trajectories (Flash and Henis, 1991; Henis and Flash, 1995; Novak et al, 2003; Roitman et al, 2004; Pasalar et al, 2005). In this manuscript we have exemplified the former approach; the analysis of the latter by means of DRD is non-trivial, and it is therefore left for future work.…”

Testing predictive control of movement in children with developmental coordination disorder using converging operations

“…This set-up provided the flexibility needed to conduct home-based measurements as no advanced 3D kinematic system was needed. The 2D registration has been shown to be valid and reliable in earlier studies (Henis & Flash, 1995;van Sonderen, Gielen, & Denier van der Gon, 1989). We chose to use the finger and not a pen or stylus as the touchpoint on the screen because handwriting problems are well known in children with DCD (Prunty, Barnett, Wilmut, & Plumb, 2013;Rosenblum & Livneh-Zirinski, 2008).…”