Sensorimotor temporal recalibration within and across limbs.

Deciding precisely when we have acted is challenging, as actions involve a train of neural events spread across both space and time. Repeated delays between actions and consequent events can result in a shift, such that immediate feedback can seem to precede the causative act. Here we examined which neurocognitive representations are affected during such sensorimotor temporal recalibration, by testing if the effect generalizes across limbs and whether it might reflect altered decision criteria for temporal judgments. Hand or foot adaptation phases were interspersed with simultaneity judgments about actions involving the same or opposite limb. Shifts in the distribution of participants' simultaneity responses were quantified using a detection-theoretic model, where a shift of both boundaries together gives a stronger indication that the effect is not simply a result of decision bias. By demonstrating that temporal recalibration occurs in the foot as well as the hand, we confirmed that it is a robust motor phenomenon: Both low and high boundaries shifted reliably in the same-limb conditions. However, in cross-limb conditions only the high boundary shifted reliably. These two patterns are interpreted to reflect a genuine change in how the time of action is represented, and a timing criterion shift, respectively.