Fig 1.
Experimental set-up and design.
(A) Overview of the set-up. (B) Information as presented on the monitor. At the onset of and during a trial, the screens displayed a graphical instruction (upper panels). Vertical bars represented the foot position as instructed, the cross represented the center from which to start, and the orange circle represented the target. The horizontal bar in the top left corner represented the progress bar. Instruction strings during the movement depended on trial type. Stochastic binary score feedback was provided following feedback trials, and “Score hidden” was displayed following non-feedback trials (lower panels). (C) Design. A baseline phase was followed by an intermittent phase. Each block contained 10 trials, except for the last block which contained 11 trials. Green-and-red blocks indicate feedback trials; blue blocks indicate non-feedback trials. White bars indicate motivation assessments.
Fig 2.
The color of the bar indicates which trials are used to estimate variability. (A) Distribution of squared trial-to-trial changes following rewarded (green) and non-rewarded (red) trials for an example participant. Vertical lines indicate the median (solid) and mean (dotted) of the distribution. (B) Variability (Δ2) on all trial types. Bars indicate the median across participants and error bars the interquartile range. Double stars indicate significant differences at p<0.01. (C) Exploration (Δη2) following non-rewarded trials, calculated based on Eq 1 plotted in the same format as panel A. Bars indicate the median across participants and error bars the interquartile range. Dots indicate the data of individual participants; the red dot indicates the example participant of panel A.
Fig 3.
Uncertainty in the estimates of variability.
(A) Uncertainty of variability (Δ2) as a function of number of trials based on which it was estimated (log-log plot). Circles indicate the median across participants. Filled circles correspond to the variability and exploration as presented in Fig 2B and 2C. The right panel provides an indication of variations across participants of this uncertainty: the error bars indicate the interquartile range across participants. (B) Variability estimates (Δ2) per non-feedback block of 10 trials in the baseline phase and in the intermittent phase, and Δ2 estimates following rewarded and non-rewarded trials per feedback block in the intermittent phase. Bars indicate the median across participants.
Fig 4.
Median of motivation scores across participants over time. Error bars indicate interquartile range. The blocks along the x-axis indicate the feedback context in the same format as Fig 1C. Motivation decreases during the baseline phase, increases during the first half of the intermittent phase and decreases again in the second half of the intermittent phase.