Dissociating the Impact of Movement Time and Energy Costs on Decision-Making and Action Initiation in Humans

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.

Quantifying the contribution of subject and group factors in brain activation

“…Similarly, it makes sense that task-based brain analyses would reveal strong similarities between subjects: given that large-scale brain anatomy is very similar across people (Hagoort, 2019; Sanes et al, 1995), the same brain areas will likely be involved for everyone in a given task. However, variations in performance from one trial or block to the next would logically depend on different mechanisms for different people (Saleri Lunazzi et al, 2021). For example, someone whose attention is captured too strongly by the visual stimuli may show lower RT with lower visual cortex activity and higher motor cortex activity.…”

Impact of decision and action outcomes on subsequent decision and action behaviors

“…The decision and motor behaviors of these subjects have been described in three recent publications reporting the effects of the decisional context on movement properties (Thura, 2020) and the effects of the motor context on decision strategies (Reynaud et al, 2020; Saleri Lunazzi et al, 2021). In these reports, subjects' behavioral adjustments are described either within a given trial (i.e.…”

“…In the first experiment (Reynaud et al, 2020; Thura, 2020), participants could invest up to 3s in the decision process and had up to 800ms to execute the reaching movement expressing a choice. In the other experiment (Saleri Lunazzi et al, 2021), the decision component of the task was similar but reaching duration was strictly bounded. By analyzing changes of several decision and motor parameters from one trial to the next, we found multiple context-dependent post-decision and post-movement outcome adjustments of both subsequent decision and motor speed-accuracy tradeoffs.…”

“…For example, human subjects decide faster and less accurately to focus on their actions when the motor context in which a choice is made is demanding (Reynaud et al, 2020). Similarly, when the temporal cost of a movement is significantly larger than usual, humans often reduce the duration of their decisions to limit the impact of these time-consuming movements (Saleri Lunazzi et al, 2021).…”

“…For example, human subjects decide faster and less accurately to focus on their actions when the motor context in which a choice is made is demanding (Reynaud et al, 2020). Similarly, when the temporal cost of a movement is significantly larger than usual, humans often reduce the duration of their decisions to limit the impact of these time-consuming movements (Saleri Lunazzi et al, 2021). Conversely, if the sensory evidence guiding the choice is weak and the deliberation takes time, humans and monkeys shorten the duration of the movement expressing that choice (Thura, 2020; Thura et al, 2014).…”