Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.06.21.163352v1?rss=1 Authors: Rens, G., Orban de Xivry, J.-J., Davare, M., van Polanen, V. Abstract: Observation of object lifting allows updating of an internal object representation for object weight, in turn enabling accurate scaling of fingertip forces when lifting the same object. Here, we investigated whether lift observation also enables updating of an internal representation for an object's weight distribution. We asked participants to grasp and lift an inverted T-shaped manipulandum with interchangeable center of mass in turns with an actor. Participants were required to minimize object roll during lifting by generating an appropriate amount of compensatory torque (i.e. lift performance) and were allowed to place their fingertips at self-chosen locations. The center of mass changed unpredictably every third to sixth trial performed by the actor and participants were informed that they would always lift the same weight distribution as the actor. Participants observed either erroneous (i.e. object rolling towards its heavy side) or skilled (i.e. minimized object roll) lifts. Lifting performance after observation was compared to lifts without prior observation and to lifts after active lifting, which would provide haptic feedback about the weight distribution. Our results show that observing both skilled and erroneous lifts can convey an object's weight distribution as similarly as active lifting, resulting in altered digit positioning strategies. However, lift performance on novel weight distributions was not improved after observing skilled lifts and only partly after observing erroneous lifts. In conclusion, these findings suggest that although observing motor errors and skilled motor performance enables updating of digit positioning strategy, only observing lifting errors enables less-than-optimal changes in predictive motor control when lifting objects with complex intrinsic properties. Copy rights belong to original authors. Visit the link for more info