Psycho & Muscle metric curve computation from a typical subject.

<p><b>A)</b> For each subject, the computation of the psychometric curve was obtained by extracting the distribution of the force level explored by the participant during the UP-DOWN staircase adaptive procedure and by fitting a logistic function to the probability of a positive answer with respect to each external force level (x). Ψ<i>ps</i>, <i>β1ps</i>, <i>β0ps</i> indicate the absolute threshold (PSE), the slope and the intercept, respectively, characterizing the logistic function that best explains the probability of detecting an upward force given each stimulus force. <b>B)</b> Computation of the muscle-metric curve was obtained by means of a weighted pool of all muscle activity (PoolEMG) and then fitting a logistic function to the probability of a PoolEMG value to be higher than the criterion per each external force level presented (x). Criterion level was set to the mean of the PoolEMG distribution (paragraph 1.4 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152552#pone.0152552.s006" target="_blank">S1 Text</a> for details). Ψ<i>emg</i>, <i>β1emg</i>, <i>β0emg</i> indicate the absolute threshold (PSE), the slope and the intercept, respectively, describing the logistic function that best explains the probability of each force level to elicit a PoolEMG value above criterion.