Improving digital object handoff using the space above the table

Object handoff - that is, passing an object or tool to another person - is an extremely common activity in collaborative tabletop work. On digital tables, object handoff is typically accomplished by sliding them on the table surface - but surface-only interactions can be slow and error-prone, particularly when there are multiple people carrying out multiple handoffs. An alternative approach is to use the space above the table for object handoff; this provides more room to move, but requires above-surface tracking. We have developed two above-the-surface handoff techniques that use simple and inexpensive tracking: a force-field technique that uses a depth camera to determine hand proximity, and an electromagnetic-field technique called ElectroTouch that provides positive indication when people touch hands over the table. We compared the new techniques to three kinds of surface-only handoff (sliding, flicking, and surface-only Force-Fields). The study showed that the above-surface techniques significantly improved both speed and accuracy, and that ElectroTouch was the best technique overall. This work provides designers with practical new techniques for substantially increasing performance and interaction richness on digital tables.