Reproduction of tracking movements and target positioning of the forearm in humans in the absence of visual control

Abstract

In 17 healthy volunteers, we studied movements of the forearm, which included episodes of positioning on the target level. The trajectory of the non-ballistic (relatively slow) movement looked like a double trapezium (flexion of the elbow joint from the state of full extension, 0 deg, positioning on the 50 deg level, further flexion to the limit angle of 100 deg, and a similar reverse sequence). The command trajectory and the trajectory of the realized movement were visualized with movements of cursors on a monitor in time/joint angle coordinates. We compared parameters of the tracking movements (in the presence of visual feedback) and their blindfold reproduction (with the complete absence of visual control). It was found that blindfold reproduction movements differ from sample tracking movements and their reproduction with partial limitation of visual control [16] in higher peak velocities and shorter durations, i.e., a trend toward conversion of such movements into ballistic ones was observed. Under conditions of elimination of visual control, movements that led to positioning were mostly hypermetric, i.e., positioning was usually accompanied by positive systematic errors (whose sign coincided with the direction of the preceding movement phase). The mean intragroup value of the systematic error of the first positioning (after flexion to the target level) was +6.73 ± 1.15 deg, while the respective mean for the second positioning (after extension to the same level) was +4.00 ± 1.31 deg. The nonlinear properties of stretch receptors of muscles whose activity provides the formation of a "proprioceptive" estimate of the joint angle are considered the crucial reason for systematic errors of blindfold positioning.

Positioning Errors in Simple Targeted Movements of the Forearm Realized in the Absence of Visual Control: Effects of Vibrational Stimulation of Antagonist Muscles

“…The experimental set was, in general, analogous to that used in our earlier works [7,8]. The subject sat in a comfortable position.…”

“…Kinesthesia is based on afferent signals mostly provided by proprioceptors (muscle spindle receptors and Golgi tendon receptors); signals from joint and cutaneous receptors probably can also play some role [1][2][3]. Blindfold reproduction becomes possible due to memorization of kinesthetic information incoming in the course of visually controlled standard movements, formation of a central motor program of the corresponding movement in the CNS, and use of kinesthetic control of the position of the limb or its link in the absence of visual information [4][5][6][7][8][9].…”

“…Such movements, however, belong, as a rule, to multijoint ones, and their muscle provision is rather complex. Examination of the simplest (one-joint) targeted movements performed within one plane (and not within 3D space) makes easier the analysis of the results obtained and can be more fruitful [5][6][7][8][9]. Nonetheless, even in these cases the comparison and interpretation of the data obtained are complicated by the above-mentioned circumstance (the variability of experimental paradigms).…”

“…Earlier, we studied in detail errors of targeted positioning under conditions of reproduction of slow (nonballistic) tracking movements of the forearm under kinesthetic control [7,8,13]. In these tests, we used relatively complex trajectories of the standard and test movements (double trapezia).…”

“…In these tests, we used relatively complex trajectories of the standard and test movements (double trapezia). Such an experimental scheme allowed us to gain an insight into the role of dissimilar motor prehistory of the target positioning episodes; this scheme, however, was related to obvious biomechanical and psychophysiological limitations and determined some difficulties of blindfold reproduction of the standard movements in a few subjects [8]. These studies demonstrated that, under conditions of limitation/ exclusion of visual control, targeted positioning is accompanied in most cases by noticeable positive systematic errors (movements of reaching the target level are usually hypermetric).…”