Abstract
Recent theories and data suggest that adapted behavior involves economic computations during which multiple trade-offs between reward value, accuracy requirement, energy expenditure, and elapsing time are solved so as to obtain rewards as soon as possible while spending the least possible amount of energy. However, the relative impact of movement energy and duration costs on perceptual decision-making and movement initiation is poorly understood. Here, we tested 31 healthy subjects on a perceptual decision-making task in which they executed reaching movements to report probabilistic choices. In distinct blocks of trials, the reaching duration (“Time” condition) and energy (“Effort” condition) costs were independently varied compared to a “Reference” block, while decision difficulty was maintained similar at the block level. Participants also performed a simple delayed-reaching (DR) task aimed at estimating movement initiation duration in each motor condition. Results in that DR task show that long duration movements extended reaction times (RTs) in most subjects, whereas energy-consuming movements led to mixed effects on RTs. In the decision task, about half of the subjects decreased their decision durations (DDs) in the Time condition, while the impact of energy on DDs were again mixed across subjects. Decision accuracy was overall similar across motor conditions. These results indicate that movement duration and, to a lesser extent, energy expenditure, idiosyncratically affect perceptual decision-making and action initiation. We propose that subjects who shortened their choices in the time-consuming condition of the decision task did so to limit a drop of reward rate.
Highlights
For humans and animals in general, life presents a constant stream of decisions about actions to make regarding food, mobility, social interactions, and many other situations
We only report data collected in the choice task but results are similar in the DR task
On average (±standard deviation (SD)), for a similar duration (642 ± 85 ms vs. 597 ± 71 ms), movement peak velocity was about twice higher in the Effort condition compared to the Reference (28.5 ± 5.3 cm/s vs. 13.3 ± 2.6 cm/s, |z| = 246.0, p < 0.001), whereas movement duration was about twice longer in the Time condition compared to the Reference condition (1,076 ± 159 ms vs. 597 ± 71 ms, |z| = 245.9, p < 0.001)
Summary
For humans and animals in general, life presents a constant stream of decisions about actions to make regarding food, mobility, social interactions, and many other situations. Individuals could benefit from maximizing accuracy and minimizing effort by making slow movements This strategy implies increasing behavior duration, which inevitably delays the completion of the task and the acquisition of the reward, leading to the well-known temporal discounting of reward value (Myerson and Green, 1995; Shadmehr et al, 2010; Haith et al, 2012; Choi et al, 2014; Berret and Jean, 2016). To summarize, both time and effort discount the value of reward, and reducing reward temporal discounting requires increasing energy expenditure, which in turn discounts the value of reward too
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