Moderate manipulation to somatosensory feedback does not affect Libet-style intentional action.

Abstract

The existence of free will has been called into question by Benjamin Libet's seminal experiment, who argued that our conscious decision is preceded by an unconscious decision reflected in the readiness potential (RP). Alternatively, it has been argue that the RP rather reflects a decision process in which different signals accumulate until they reach the intention threshold, at which point an agent experience their intention simultaneously. This raises the question what type of signal is accumulated given that no external information is provided. Recent studies suggest that various interoceptive signals, such as the respiratory and cardiac cycles, guide our arbitrary decisions. We hypothesized the somatosensory feedback from the afferent system could be another potential source, and tested this by inducing numbness in participants' hands. If somatosensory feedback is one source of information in arbitrary decisions, participants should take longer to reach the decision threshold. Contrary to our hypotheses, Bayesian analyses revealed decisive evidence supporting the null hypothesis. These findings suggest that somatosensory feedback may not substantially contribute to arbitrary decisions, and alternative explanations have been proposed to account for the results.