Speed—Accuracy Tradeoffs in Aimed Movements: Toward a Theory of Rapid Voluntary Action (original) (raw)
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Making a movement may be thought of as an economic decision in which one spends effort in order to acquire reward. Time discounts reward, which predicts that the magnitude of reward should affect movement vigor: we should move faster, spending greater effort, when there is greater reward at stake. Indeed, saccade peak velocities are greater and reaction-times are shorter when a target is paired with reward. Here, we focused on human reaching and asked whether movement kinematics were affected by expectation of reward. Participants made out-and-back reaching movements to one of four quadrants of a 14cm circle. During various periods of the experiment only one of the four quadrants was paired with reward, and the transition from reward to non-reward status of a quadrant occurred randomly. Our experiment design minimized dependence of reward on accuracy, granting the subjects wide latitude in self-selecting their movement speed, amplitude, and variability. When a quadrant was paired wi...
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When deciding between alternative options, a rational agent chooses on the basis of the desirability of each outcome, including associated costs. As different options typically result in different actions, the effort associated with each action is an essential cost parameter. How do humans discount physical effort when deciding between movements? We used an action-selection task to characterize how subjective effort depends on the parameters of arm transport movements and controlled for potential confounding factors such as delay discounting and performance. First, by repeatedly asking subjects to choose between 2 arm movements of different amplitudes or durations, performed against different levels of force, we identified parameter combinations that subjects experienced as identical in effort (isoeffort curves). Movements with a long duration were judged more effortful than short-duration movements against the same force, while movement amplitudes did not influence effort. Biomecha...
Context influences on the preparation and execution of reaching movements
Cognitive Neuropsychology, 2008
The ability of rapidly adapting our motor behaviour in order to face the unpredictable changes in the surrounding environment is fundamental for survival. To achieve such a high level of efficiency our motor system has to assess continuously the context in which it acts, gathering all available information that can be relevant for planning goal-oriented movements. One still-debated aspect of movement organization is the nature and timing of motor planning. While motor plans are often taken to be concerned with the setting of kinematic parameters as a function of perceptual and motor factors, it has been suggested that higher level, cognitive factors may also affect planning. To explore this issue further, we asked 18 right-handed human participants to perform speeded hand-reaching movement toward a visual target in two different experimental settings, a reaction time (RT) paradigm (go-only task) and a countermanding paradigm. In both tasks participants executed the same movements, but in the countermanding task no-stop trials were randomly intermixed with stop trials. In stop trials participants were required to withhold the ongoing movement whenever a stop signal was shown. It is known that the presence of stop trials induces a consistent increase of the RTs of no-stop trials with respect to the RTs of go-only trials. However, nothing is known about a similar effect for movement times (MTs). We found that RTs and MTs exhibit opposing tendencies, so that a decrease in the RT correspond to an increase in the MT and vice versa. This tendency was present in all our participants and significant in 90% of them. Furthermore we found a moderate, but again very consistent, anticorrelation between RTs and MTs on a trial-by-trial base. These findings are consistent with strategic changes in movement programmes for the very same movements under different cognitive contexts, requiring different degrees of feedback-driven control during movement.