A multi-measurement study of the relation between deliberation and volition

Abstract

Historically, voluntary action and volition more generally have been investigated through the lens of meaningless decisions. Importantly, these findings have been used in the debate about key notions like free will and moral responsibility. However, more recent claims have challenged the possibility of generalizing findings from a meaningless context to a more meaningful one. The current study investigates the markers of volition, specifically comparing meaningful and meaningless decisions. In an effort to maximize their monetary gain, 50 participants repeatedly deliberated between two options, making either rewarded choices-hard-deliberation decisions (where the options differed along two dimensions) or easy-deliberation decisions (where the options differed along a single dimension)-or unrewarded choices, a.k.a. arbitrary decision. This enabled us to contrast rewarded and unrewarded decisions as well as the degree of deliberation between easy- and hard-deliberation choices. We found evidence that rewarded and unrewarded decisions differed along several measures related to volition: participants reported a higher sense of volition, exhibited a stronger Readiness Potential, had increased temporal binding (mostly inconclusive), and demonstrated increased Effort Exerted in the rewarded condition. In contrast, we found evidence for similarity across these measures between easy-deliberation and hard-deliberation conditions. Our results suggest that it is not the complexity of the deliberation process prior to the action that makes it more volitional, but rather that the decision serves a meaningful goal. Our study also introduced a new implicit measure of volition- effort exerted-that well aligned with other measures of volition and should therefore prove useful in future studies.

Keywords: agency; intention; volition.

Figure 1

Task design. The participant’s task was to maximize the overall number of neuros (N, a symbolic coin that was linearly translated into a monetary reward) during the experiment. (A) During the task, first the buckets were presented until the participant squeezed the handgrip. The number of neuros associated with the buckets, balloons, and tokens depended on the condition (see B for more details). The handgrip was unresponsive for the first second to make sure the participants took the time to take in the information. The participants were then instructed to focus on the fixation cross for 1.7 s, after which the two pairs of balloons and tokens were presented, each with how much they would increase the fill level of their associated bucket (shown as a proportion for the balloon and as a number (out of a maximum of 17) for the token). They had to select one of them by squeezing the handgrip in their ipsilateral hand. Again, the handgrip was unresponsive for 1 s. After their selection, there was a delay of 200, 500, or 800 ms (uniformly distributed among the three options) before a beep sounded and a white ellipse encircled the selected pair. At that time, participants estimated the time interval between their hand press and the beep using the mouse. Once they clicked the mouse, the next trial started, with the buckets’ fill level updated according to the participant’s choice. (B) The conditions were differentiated only by the values attached to the buckets (and hence to the balloon and token). In the arbitrary condition, none of the buckets could increase the reward. In the Easy Deliberation condition, only one of the two systems was activated, and in the Hard Deliberation condition, both systems were activated.

Figure 2

Reported Deliberation. (A) In each boxplot, the thick horizontal black line represents the median. The top and bottom parts of the box represent the 75% and 25% percentiles of the data. The vertical lines represent the 1.5 interquartile range starting from the 25% percentile at the bottom and the 75% percentile on top. Each line connecting the boxplots and dots represents the Reported Deliberation of a single participant. H1 represents evidence for a difference (see Statistical analysis for more details). (B) Posterior analysis of Reported Deliberation. Each column represents the posterior distribution of the difference between two conditions (e.g. “Arbitrary - Easy-deliberation,” is the resulting posterior distribution of the arbitrary minus the Easy Deliberation condition). The distribution of the prior used to run the model and to calculate the BF₁₀ is in orange. It has a normal distribution centered on 0 with a SD of 25. The blue distribution is the posterior distribution, with the 89% HDI (in darker blue). The dashed vertical line is at 0 (no difference).

Figure 3

RT. (A) Similar as Fig. 2A. H₀ represents evidence for similarity and H₁ for difference. (B) Posterior analysis of the RTs. Similar as Fig. 2B. Here, the SD of the prior distribution (in orange) is 1.

Figure 4

Self-reported SoV. (A) Similar as Fig. 2A. H₀ represents evidence for similarity and H₁ for difference. (B) Posterior analysis of the reported SoV. Similar as Fig. 2B. The SD of the prior distribution (in orange) is 25.

Figure 5

EEG plot of the RP. Each line represents a condition with its 95% confidence interval (i.e. the shaded area around each curve). The curves represent activity from the Cz electrode, time-locked on the hand press.

Figure 6

Slope of the RP. (A) Similar as Fig. 2A. H₀ represents evidence for similarity, H₁ for difference, and inconclusive H₁ represents inconclusive evidence for H₁ (i.e. PD above 95% and HDI89% not overlapping 0, but BF₁₀ inconclusive). (B) Posterior analysis of the slope of the RP. Similar as Fig. 2B. The SD of the prior distribution (in orange) is 1.

Figure 7

Mean of the RP. (A) Similar as Fig. 2A. H₀ represents evidence for similarity, H₁ for difference, and inconclusive H₁ represents inconclusive evidence for H₁ (i.e. PD above 95% and HDI89% not overlapping 0, but BF₁₀ inconclusive). (B) Posterior analysis of the mean of the RP. Similar as Fig. 2B. The SD of the prior distribution (in orange) is 1.

Figure 8

TB measured with interval estimation, separated by real action-tone delays. (A, C, E) Similar as Fig. 2A. H₀ represents evidence for similarity, H₁ for difference, inconclusive H₁ represents inconclusive evidence for H₁ (i.e. PD above 95% and HDI89% not overlapping 0, but BF₁₀ inconclusive) and inconclusive H₀ represents inconclusive evidence for H0 (i.e. PD below 95%, BF₁₀ inconclusive, but RR_IN indicating a prior change of conclusion being more likely for H₀ than H₁. (B, D, F) Posterior analysis of the TB. Similar as Fig. 2B. The SD of the prior distribution (in orange) is 30.

Figure 9

Effort exerted (EE). (A) Similar as Fig. 2A. H₀ represents evidence for similarity and H₁ for difference. (B) Posterior analysis of the EE. Similar as Fig. 2B. The SD of the prior distribution (in orange) is 10.