Foi analisado o efeito de restrições espaciais (distância e tamanho do alvo) sobre as estratégias de controle motor em movimentos rápidos e precisos. Vinte homens (20-26 anos) realizaram a tarefa de Fitts simulada em computador. O software Discrete Aiming Task (v.1.0) forneceu a análise cinemática do cursor do mouse e a manipulação de índices de dificuldade (1 até 5 bits). O acréscimo na distância aumentou o TM, fase de aceleração, fase de desaceleração e velocidade, mas sem alterar a precisão. A manutenção na precisão foi explicada pela estratégia da manutenção na proporção entre as fases de aceleração e desaceleração. A redução do alvo proporcionou maiores TM e fase de desaceleração e diminuição do maior valor de velocidade, que permitiram maior precisão mesmo com a manutenção na velocidade média. Diferentes estratégias de controle motor foram realizadas em função da restrição espacial manipulada pela distância e pelo tamanho do alvo. Palavras-chave: restrição espacial, distância, tamanho do alvo, velocidade-precisão, controle motor ABSTRACT The effect of spatial constraints (distance and target width) was analyzed over the motor control strategies of speed and accurate movements. Twenty men (20-26 years old) performed the Fitts' task simulated in a computer. The Discrete Aiming Task (v.1.0) provided the kinematic analysis of the mouse cursor and the index of difficulties manipulation (1 to 5 bits). Distance increased provided great TM, acceleration phase, deceleration phase, and velocity, but without changing accuracy. Accuracy maintenance was explained by the maintenance of acceleration and deceleration phases' strategy. Target width decrease provided greater TM and deceleration phase and reduction of the peak velocity, which allowed better accuracy even when average velocity was held constant. Different control strategies were performed in function of the spatial constraint manipulated by the distance and target width.

Purpose. The effects of practice were analyzed in the control of fast and accurate spatially constrained movements. Methods. Twenty men (20-26 years old) evenly divided into an experimental and control group were analyzed in three time periods: pre-test, post-test, and retention. Discrete Aiming Task ver. 2.0 software simulated Fitts’ task (1954) and provided kinematic analysis of mouse cursor movements (displacement, velocity, and acceleration). The task consisted of using the mouse to click on two parallel targets as fast and accurately as possible. Four target widths (W = 2.0, 1.0, 0.5, and 2.5 inches) and three distances between the targets (D = 2.0, 4.0, and 8.0 inches) were used to provide indexes of difficulty (ID) from 1 to 6 bits. The experimental group performed 108 practice trials (three blocks of 36 trials on different days) while the control group had no practice. Results. Movement time (MT) decreased in the experimental group largely due in part to a reduction of time used for feedback. It is suggested that the improvement in performance as a function of practice occurred through the interdependence of programming and the feedback process. As the task was practiced, there was decreased need for feedback due to better pre-programming of the primary submovement and the improved use of sensorial feedback information. This strategy and a lengthened deceleration phase can help explain the paradigm of fast and accurate movement as a result of practice. Conclusions. Despite the improved performance changes as a consequence of practice, Fitts’ Law proved to be robust enough to predict MT as a function of ID.

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