Sub-Optimal Allocation of Time in Sequential Movements

Abstract

The allocation of limited resources such as time or energy is a core problem that organisms face when planning complex actions. Most previous research concerning planning of movement has focused on the planning of single, isolated movements. Here we investigated the allocation of time in a pointing task where human subjects attempted to touch two targets in a specified order to earn monetary rewards. Subjects were required to complete both movements within a limited time but could freely allocate the available time between the movements. The time constraint presents an allocation problem to the subjects: the more time spent on one movement, the less time is available for the other. In different conditions we assigned different rewards to the two tokens. How the subject allocated time between movements affected their expected gain on each trial. We also varied the angle between the first and second movements and the length of the second movement. Based on our results, we developed and tested a model of speed-accuracy tradeoff for sequential movements. Using this model we could predict the time allocation that would maximize the expected gain of each subject in each experimental condition. We compared human performance with predicted optimal performance. We found that all subjects allocated time sub-optimally, spending more time than they should on the first movement even when the reward of the second target was five times larger than the first. We conclude that the movement planning system fails to maximize expected reward in planning sequences of as few as two movements and discuss possible interpretations drawn from economic theory.

Эффект «проигрыша» При Выполнении Простой Сенсомоторной Задачи В Ситуации Соревнования

“…We believe that the observed errors are related to an increase in the specific value of a particular trial within the general context. We did not see increased performance after hits, and this matches the data collected by Wu (Wu et al, 2009). However, we revealed errors related to a reactive effect: competition shows an increased share of errors caused by one's own miss in the previous trial.…”

“…Other research (Wu et al, 2009) revealed rather ambiguous results, but demonstrated that the way the participants used time given for a specific task is also suboptimal. The participants had to sequentially hit two targets that appeared on the screen within a limited period of time with no specific limitations on time distribution within the task itself.…”

Adaptive Allocation of Vision under Competing Task Demands

“…This hypothesis was based, in part, on results in another experiment that demonstrated sub-optimal motor planning in sequential pointing tasks (Wu, Dal Martello, & Maloney, 2009). In the Wu et al study, subjects executed a sequence of hand movements to touch two targets.…”

Motor control is decision-making

“…Surprisingly, motor decisions concerning planned sequences of movements under risk turn out to be suboptimal. When subjects have a fixed time within which to try to sequentially hit two targets, each associated with a different reward, there is a tradeoff in the time allocated to each movement, and performance is suboptimal [15]. Subjects spend too much time on the first reach even when hits on the second target are far more valuable than on the first.…”