The iterative development of a tangible pin-board to symmetrically link physical and digital documents

There is an asymmetry in many tangible interfaces: while physical objects can be used to manipulate digital information, the reverse is often not possible—the digital world cannot push back. We introduce a new push-back tangible technology, a pin-board that physically ejects paper documents. This is realized by extending the Pin&Play technology to support ‘pouts’, addressable pin-like devices that can remove themselves from a board using muscle wire actuators. We describe how this technology has been developed through two iterations of prototyping, application and formative study. An initial study revealed how potential mismatches between the physical and digital characteristics of pouts caused difficulties with users predicting pop-out events and reasoning about the state of pouts. This led us to extend pouts to reveal more of their internal state, an approach verified through a second study. It also raises more general issues for the design of pushback tangible technologies and ubiquitous interfaces.