Experimental Analysis of Human Control Strategies in Contact Manipulation Tasks

Here, we present insights into human contact-control strategies by defining conditions to determine whether a human controls a contact state, empirically analyzing object-to-environment contact geometry data obtained from human demonstrations in a haptic simulation environment, and testing hypothesess about underlying human contact-control strategies. Using haptic demonstration data from eleven subjects who inserted non-convex objects into occluded holes, we tested the following human contact-control hypotheses: (h1) humans follow a task trajectory that tracks pre-planned contact-state waypoints organized in a contact-state graph (contact-waypoint hypothesis); (h2) humans traverse the contact-state graph, explicitly controlling some contact states or subsets of contact states, in addition to the pre-determined initial and final goal states (controlled subgraph hypothesis); (h3) humans use a control policy where the only controlled states are the starting state for the task and the goal state (state policy hypothesis). Notably, we found that humans tend to visit a select few contact states once they enter each state’s vicinity in the graph, which is evidence against h3. Yet humans do not always visit said states (visit probability \(<40\%\)), which is, in addition, evidence against h1 provided different humans adopt similar strategies. We show that a classifier to determine when humans control their trajectories to visit specific contact states, when parameterized correctly, is invariant to graph aggregation operations across the false-positive to false-negative tradeoff spectrum. This indicates our results are robust given the data we obtained and suggests that efforts to characterize human motion should focus on h2.