Optimality in human motor performance: Ideal control of rapid aimed movements.

Abstract

A stochastic optimized-submovement model is proposed for Pitts' law, the classic logarithmic tradeoff between the duration and spatial precision of rapid aimed movements. According to the model, an aimed movement toward a specified target region involves a primary submovement and an optional secondary corrective submovement. The submovements are assumed to be programmed such that they minimize average total movement time while maintaining a high frequency of target hits. The programming process achieves this minimization by optimally adjusting the average magnitudes and durations of noisy neuromotor force pulses used to generate the submovements. Numerous results from the literature on human motor performance may be explained in these terms. Two new experiments on rapid wrist rotations yield additional support for the stochastic optimizedsubmovement model. Experiment 1 revealed that the mean durations of primary submovements and of secondary submovements, not just average total movement times, conform to a square-root approximation of Pitts' law derived from the model. Also, the spatial endpoints of primary submovements have standard deviations that increase linearly with average primary-submovement velocity, and the average primary-submovement velocity influences the relative frequencies of secondary submovements, as predicted by the model. During Experiment 2, these results were replicated and extended under conditions in which subjects made movements without concurrent visual feedback. This replication suggests that submovement optimization may be a pervasive property of movement production. The present conceptual framework provides insights into principles of motor performance, and it links the study of physical action to research on sensation, perception, and cognition, where psychologists have been concerned for some time about the degree to which mental processes incorporate rational and normative rules. An enduring issue in the study of the human mind concerns of mathematical probability theory and statistical decision thethe rationality and optimality of the mental processes that guide ory (e.g.,

Context-dependent arm pointing adaptation

“…Subjects typically perform movement corrections during adaptation experiments, evident as corrective submovements in the velocity profile [16,20], especially towards the beginning of the adaptation blocks when they are learning the task and adapting to the change in the gain of display. Since the focus of interest was more in how the subjects preplanned the movements and less in the on-line corrections that they made, we decomposed the movement into its primary and secondary submovements.…”

“…Since the focus of interest was more in how the subjects preplanned the movements and less in the on-line corrections that they made, we decomposed the movement into its primary and secondary submovements. The primary submovement is thought to be mostly under ballistic control whereas the secondary submovement reflects a feedback-based correction [20]. The existence of secondary submovements was determined using an algorithm that searches for a positive acceleration value following a period of deceleration, or a change in the sign of the velocity, signifying a change in movement direction.…”

“…Our previous work [20] suggests that the visuomotor map in use for arm pointing is functionally linked to that in use for head pointing, even when the head is restrained during arm pointing. The existing literature on eye-head-hand coordination provides substantial evidence for integrated, synergistic control of these body segments [2,8,29].…”

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

“…These two components have been referred to as the primary and secondary 49 submovement(s), respectively (e.g., Meyer et al 1988). The primary submovement is considered 50 to reflect the planning processes that occur prior to movement onset, while secondary 51 submovement(s) is (are) considered to be guided by a process of online control that reduces any added cost is due to the former involving a longer path to the target, the reversal of a zero-inertia 92 situation (i.e., a secondary acceleration in the direction opposite to the initial direction of travel) 93 and a reversal in the roles of the agonist and antagonist muscle groups ).…”

Insight into Goal-Directed Movements: Beyond Fitts’ Law

“…The first approach considers characteristics of the overall movement, such as total time or throughput (Fitts' Law). The second approach, mostly found in human movement research, assumes that a movement consists of several submovements and that this division may reveal distinct information about the quality of the overall movement [10,16]. Although both approaches have proven to be helpful in comparing input devices or interaction techniques [15,1,9,18] it is difficult to use them to distinguish different movement strategies and to apply these approaches to the design of input devices and interaction techniques.…”