Models for the speed and accuracy of aimed movements.

Abstract

Some alternative relations between the speed and accuracy of aimed limb movements are considered. According to one relation, Pitts' law, movement time is a logarithmic function of the movement distance divided by the width of the target toward which the movement proceeds [ T = C, + C 2 log 2 (2.D/ W)], According to a second relation, discovered by Schmidt, Zelaznik, Hawkins, Frank, and Quinn (1979), movement error (deviation from the target center) is a linear function of the movement distance divided by the movement time [ W e = K(D/ T)]. Previous explanations of this second relation, based on an asymmetric impulse-variability model, are mathematically faulty and violate well-known physical principles. However, a new symmetric impulse-variability model can explain the linear relation more adequately. The latter model assumes that a limb is driven by the product of a force parameter and a time function with certain welldefined qualitative properties, including symmetry, curvilinearity, and force-time rescalabUity. In combination, these properties correctly predict the observed linear speed-accuracy trade-off for aimed movements and agree with other known aspects of movement dynamics. They may be realized in terms of underlying biomechanical (e.g., mass-spring) and neurophysiological (e.g., electromyographic) mechanisms. The symmetric impulse-variability model also provides a possible way to account for Pitts' law, unifying the logarithmic speedaccuracy trade-off with the linear trade-off.In moving a limb such as an arm from one less accurate on the average, and movements position to another, it is often necessary for having greater spatial accuracy can usually a person to make some compromise between occur only at the expense of being slower on the duration and spatial precision of the the average. Thus a speed-accuracy trade-off movement. Faster movements can usually influences movement control just as it does occur only at the expense of being spatially mental processes like perception, memory, and thought (Pachella, 1974). .Of course, there are certain limits to this The authors express their gratitude to Sylvan Korn-trade-off. It does not seem to have much, if blum for many helpful criticisms and suggestions about any, effect on movements with very low vean earlier version of this paper We also thank Richard lodty and me tempora i precision of move-SSS^^ ™nts ^n actually increase as their velocity University of Michigan's Human Performance Center increases (Newell, 1980). Nevertheless, the and at Bell Laboratories for enthusiastic discussions and trade-off between speed and spatial accuracy encouragement regarding the material presented here. j s an important phenomenon whose nature Requests for reprints should be sent to David E. h rnainr rompmienres for manv tvnes of Meyer, Human Performance Center, Department of has maj °r con S ec l u ences tor many types OI Psychology, University of Michigan, 330 Packard Road, amwxl movement. Whenever someone moves Ann Arbor, Michigan 48104.an arm to point toward some lo...

Minimum Principles in Motor Control

“…On the behavioral level, this is a well-established phenomenon. When participants are instructed to repeatedly produce identical movements of prescribed amplitude and duration, they instead produce a distribution of movements that is characterized by a scattering of endpoints whose standard deviation scales linearly with average movement speed (Schmidt et al, 1979;Meyer, Smith, 6 Wright 1982); quite apparently, participants do not and cannot produce identical movements across a series of trials. In addition to the behavioral evidence, there is physiological data suggesting that stochasticity is, in fact, a fundamental characteristic of neural information processing (Calvin 6 Stevens, 1968;Clamann, 1969).…”

“…One example is the logarithmic speed accuracy trade-off, known as Fitts's law (Fitts, 1954). Empirically, this law has proved extremely robust across a plethora of motor activities and experimental conditions (e.g., Kerr, 1973;Langolf, Chaffin, 6 Foulke, 1976;Meyer et al, 1982). Its interpretation, however, has been highly controversial.…”

Do Synergies Improve Accuracy? A Study of Speed-Accuracy Trade-Offs during Finger Force Production

“…Fitts' law has been confirmed over a variety of populations, conditions and tasks, including isometric force production tasks (Kantowicz and Elvers 1988;Billon, Bootsma, and Mottet, 2000). Although the location of mechanisms that produce Fitts' law is still under debate (Meyer, Smith, and Wright, 1982;Plamondon and Alimi 1997), it is likely to reflect processes at the level of motor planning (Gutman and Latash 1993;Duarte and Latash 2007).…”

Troca velocidade-acurácia em tarefa de contornar figuras geométricas

“…Assim, Woodworth (1899) apontou que a menor possibilidade de utilização de feedback, para as correções necessárias que garantam a acurácia no movimento, seria a principal responsável pela relação inversa velocidadeacurácia. Suporte para a explicação da relação inversa velocidade-acurácia através da utilização do feedback também foi verificada em estudos posteriores (CROSSMAN;GOODEVE, 1963GOODEVE, /1983BEGGS;HOWART, 1972;MEYER et al, 1982MEYER et al, , 1988. Entretanto, foi a partir da explicação fornecida por Paul Fitts (FITTS, 1954;FITTS;PETERSEN, 1964), que conseguiu expressar matematicamente esta relação inversa, que este paradigma ficou mais conhecido.…”