Motor-output variability: A theory for the accuracy of rapid motor acts.

Abstract

Theoretical accounts of the speed-accuracy trade-off in rapid movement have usually focused on within-movement error detection and correction, and have consistently ignored the possibility that motor-output variability might be predictably related to movement amplitude and movement time. This article presents a theory of motor-output variability that accounts for the relationship among the movement amplitude, movement time, the mass to be moved, and the resulting movement error. Predictions are derived from physical principles; empirical evidence supporting the principles is presented for three movement paradigms (single-aiming responses, reciprocal movements, and rapid-timing tasks); and the theory and data are discussed in terms of past theoretical accounts and future research directions. Examining the current level of understanding about the production and control of motor responses, many would no doubt be tempted to say that we have not come very far since the early writings of Woodworth (1899) and Hollingworth (1909). These writers were concerned with the basic laws of limb movements (analogous, perhaps to the basic laws of motion that were the cornerstone of physics) that denned the relationship between the simplest aspects of motor

Common vs. independent limb control in sequential vertical aiming: The cost of potential errors during extensions and reversals

“…For CE, there were no significant main effects of 5.0mm). These findings align with suggestions that greater movement displacement, as in the one-component movement toward the far target, is associated with increased movement variability (Schmidt et al, 1979). Moreover, these analyses are consistent with the idea that online control prior to or during the second movement component had the effect of reducing endpoint dispersion.…”

“…According to the optimized submovement model (Meyer, Abram, Kornblum, Wright, & Smith, 1988), these movement phases are coordinated so as to optimize the relationship between variability associated with ballistic movements (Schmidt, Zelaznik, Hawkins, Frank, & Quinn, 1979) and the time-consuming error corrections designed to successfully land on the target. A central tenet of this optimization is that the initial submovement endpoints of goal-directed aims form a normal distribution centred on the middle of the target (Meyer et al, 1988).…”

Effector mass and trajectory optimization in the online regulation of goal-directed movement

“…These results reflect the fact that movements with the heavy 342 stylus involved the specification of greater force (see Schmidt et al 1979). According to the 343 Stylus by Group interaction, movements with the heavy stylus were more variable than those 344 with the light stylus in the RPK and RNK groups; whereas there was no difference between styli 345 in the B group (see Figure 3).…”

Motor preparation of spatially and temporally defined movements: evidence from startle

“…a required movement time produced a linear relationship between speed and accuracy, whereby faster movements produced more variability of endpoint and thus less accurate performance (Schmidt et al 1978(Schmidt et al , 1979. One reason given for the difference in the speed-accuracy trade-off was a difference in the movement goal, because in one scenario movement time is controlled, whereas in the other spatial accuracy is maintained and controlled (Zelaznik et al 1988).…”