Intermittency in the Control of Continuous Force Production

Abstract

The purpose of the current investigation was to examine the influence of intermittency in visual information processes on intermittency in the control continuous force production. Adult human participants were required to maintain force at, and minimize variability around, a force target over an extended duration (15 s), while the intermittency of on-line visual feedback presentation was varied across conditions. This was accomplished by varying the frequency of successive force-feedback deliveries presented on a video display. As a function of a 128-fold increase in feedback frequency (0.2 to 25.6 Hz), performance quality improved according to hyperbolic functions (e.g., force variability decayed), reaching asymptotic values near the 6.4-Hz feedback frequency level. Thus, the briefest interval over which visual information could be integrated and used to correct errors in motor output was approximately 150 ms. The observed reductions in force variability were correlated with parallel declines in spectral power at about 1 Hz in the frequency profile of force output. In contrast, power at higher frequencies in the force output spectrum were uncorrelated with increases in feedback frequency. Thus, there was a considerable lag between the generation of motor output corrections (1 Hz) and the processing of visual feedback information (6.4 Hz). To reconcile these differences in visual and motor processing times, we proposed a model where error information is accumulated by visual information processes at a maximum frequency of 6.4 per second, and the motor system generates a correction on the basis of the accumulated information at the end of each 1-s interval.

Effects of visual feedback absence on force control during isometric contraction

“…Overall, our results reveal a lower complexity (signal noise in its time domain structure) of the force variability without vision, which is consistent with earlier studies showing that the complexity of the force variability decreases when less visual information is provided (Slifkin et al 2000).…”

“…The success in maintaining the required force target, indeed, has been found to be strongly influenced by the modality (Slifkin et al 2000;Miall et al 1993), delay (Sosnoff and Newell 2007;Miall et al 1985) and gain (number of pixels on the screen per unit of force) with which the visual feedback is shown to the subject (Sosnoff and Newell 2005 , 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2006; Vaillancourt et al 2006). Slifkin et al (2000) investigated the influence of different gains of visual feedback during sustained isometric contraction of the index flexor. The gain was found to be directly correlated to force accuracy (i.e., a precision of force signal with respect to the target) and inversely correlated to force stability (i.e., a degree of force signal fluctuation as the ratio of mean force output over the within-participant standard deviation).…”

“…Visual feedback, indeed, has been either removed during isometric contraction (Schiffman et al 2002;Tracy 2007b) or provided intermittently throughout the task (Slifkin et al 2000;Baweja et al 2009;Madeleine et al 2002). During an isometric task without visual feedback following the same task performed with the aid of visual feedback, force output can be reasonably supposed to be handled by the central nervous system in a different way because of an altered somatosensory feedback involvement.…”

“…Given that the complexity of the force variability decreases when less visual information is provided (Slifkin et al 2000), hypothesis can be made that when visual feedback is not provided, force control relies on the ability to maintain force accuracy and stability by exteroceptive and proprioceptive information and by the memory of a previous identical task. To this purpose, participants performed sustained isometric tasks at different contraction intensities, with and in the complete absence of visual feedback.…”

Efeito da posição da articulação do cotovelo no controle de torque de supinação do antebraço em jovens adultos

“…these findings agree with those of previous studies 26,30 , which also reported less precision at higher strength levels. RmS error, used as a precision measure, reflected the subject's difficulty in reaching the target which, in this case, meant reaching the relative torque level required and keeping it constant and continuos.…”