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What makes a reach movement effortful? Physical effort discounting supports common minimization principles in decision making and motor control.

ABSTRACT: 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. Biomechanics of the movements also affected effort, as movements towards the body midline were preferred to movements away from it. Second, by introducing movement repetitions, we further determined that the cost function for choosing between effortful movements had a quadratic relationship with force, while choices were made on the basis of the logarithm of these costs. Our results show that effort-based action selection during reaching cannot easily be explained by metabolic costs. Instead, force-loaded reaches, a widely occurring natural behavior, imposed an effort cost for decision making similar to cost functions in motor control. Our results thereby support the idea that motor control and economic choice are governed by partly overlapping optimization principles.

SUBMITTER: Morel P

PROVIDER: S-EPMC5460791 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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What makes a reach movement effortful? Physical effort discounting supports common minimization principles in decision making and motor control.

Morel Pierre P Ulbrich Philipp P Gail Alexander A

PLoS biology 20170606 6

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 potentia ...[more]

PMID: 28586347

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Project description:Previous research has shown that the prospect of attaining a reward can promote task-engagement, up-regulate attention toward reward-relevant information, and facilitate enhanced encoding of new information into declarative memory. However, past research on reward-based enhancement of declarative memory has focused primarily on paradigms in which rewards are contingent upon accurate responses. Yet, findings from test-enhanced learning show that making errors can also be useful for learning if those errors represent effortful retrieval attempts and are followed by corrective feedback. Here, we used a challenging general knowledge task to examine the effects of explicitly rewarding retrieval effort, defined as a semantically plausible answer to a question (referenced to a semantic knowledge database www.mangelslab.org/bknorms), regardless of response accuracy. In particular, we asked whether intermittent rewards following effortful incorrect responses facilitated learning from corrective feedback as measured by incidental learning outcomes on a 24-48 h delayed retest. Given that effort-contingent extrinsic rewards represent the intersection between an internal locus of control and competency, we compared participants in this "Effort" group to three other groups in a between-subjects design: a Luck group that framed rewards as related to participant-chosen lottery numbers (reward with internal control, not competence-based), a random Award group that framed rewards as computer generated (no control, not competence-based), and a Control group with no reward, but matched on all other task features. Both men and women in the Effort group showed increased self-reports of concentration and positive feelings following the receipt of rewards, as well as subjective effort on the retest, compared to the Control group. However, only women additionally exhibited performance benefits of effort framing on error correction. These benefits were found for both rewarded and non-rewarded trials, but only for correction of low confidence errors, suggesting that effort-contingent rewards produced task-level changes in motivation to learn less familiar information in women, rather than trial-level influences in encoding or consolidation. The Luck and Award groups did not demonstrate significant motivational or behavioral benefits for either gender. These results suggest that both reward context and gender are important factors contributing to the effectiveness of rewards as tools to enhance learning from errors.

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What makes a reach movement effortful? Physical effort discounting supports common minimization principles in decision making and motor control.

Publications

What makes a reach movement effortful? Physical effort discounting supports common minimization principles in decision making and motor control.

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