Movement control characteristics of aiming responses.

This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Two experiments were conducted investigating the movement patterns produced in the completion of aiming responses. Movement displacement, velocity and acceleration patterns were examined in the first experiment in an attempt to determine the control processes used in discrete, peg transfer and reciprocal tapping tasks. The kinematic parameters indicated that each of these tasks were characterized by discrete error corrections occurring near the target. Experiment 2 demonstrated that under high index of difficulty conditions responses are characterized by multiple discrete corrections designed to eliminate the discrepancy between the position of the hand and the target. These findings are discussed in relation to a discrete feedback interpretation of Fitts' law. I. Introduction Even with the recent growth of interest in motor control processes, the work of Fitts (Fitts 1954, Fitts and Peterson 1964) still remains as one of the few precise laws describing motor performance (Kerr 1978). Fitts (1954) quantified the relationship among movement speed, amplitude and accuracy in aiming responses, showing that movement time (MT) could be predicted from the formula MT=a+blog 2 (2Ajw), where A is the amplitude of the movement, W is the width of the target and a and bare constants. This formula predicts linear increases in MT with increases in the index of difficulty of the task; the index of difficulty (ID) being defined as, ID = log, (2AjW). Adjustments to' Fitts' law have been suggested (Welford 1968) but in general the law tends to hold in a variety of experimental situations (for example, Fitts and Peterson 1964, Kerr 1973, Langolf et al. 1976) and across a broad perspective of populations (for example, Welford et al, 1969, Wade et al. 1978). Various control processes have been hypothesized in order to account for this …