Visual estimation of the force applied by another person

As observers, we believe that we can visually estimate the force that another person applies to an object. However, it is unclear what kind of cues we use to do this. We have focused on two types of visual change that occur when a person pushes an elastic object from above with his or her finger: the first one relates to a finger/hand shaking, known as an ``induced tremor'' and the second one relates to object deformation due to the application of force. This study shows that human observers of videos combine these two visual cues to estimate the force being applied by another person in the videos. Overall, the apparent force was stronger when the shaking was larger and when the magnitude of the deformation was larger, although systematic individual differences existed. The estimation of force was likely made in separate cognitive functions from the estimation of object softness. Estimating the force that another person applies seems to be done by perceptually interpreting both the actions of others and their external outcomes.