It was a difficult choice deciding which article to spotlight this month. As such, I decided to feature two articles most prominently in my editorial for Issue 23:2, the first of which forms the subject matter of this post.

But as it so happens, both of the articles I spotlighted this month consider the issues and challenges raised by mixed-reality spaces from unique perspectives.

And both take an inter-disciplinary tack on the difficult problems raised by this intriguing class of ubiquitous computing systems.

Nonetheless, as GPS and other sensors indeed live up to the name of this sub-field and become truly ubiquitous, it speaks to experiences (and usability problems) that we have all already likely encountered in one form or another as we fumble about in an unfamiliar city with our smartphones in hand.

Or that we will all likely encounter in the future, as our physical abilities inevitably change or diminish with age.



Lions, Impala, and Bigraphs—A Unique Perspective on Modeling Physical / Virtual Spaces

They say the three most important things in real estate are location, location, and location—and so it seems with ubiquitous computing systems, and contextual interactions in general.

Yet what is less often recognized is that ‘location’ is, in fact, a social construct every bit as much as it is physical property of the world—and which furthermore can only be sensed through particular technologies that have their own quirks. As the authors of this article make apparent, the result is a many-faceted terrain that offers shifting perspectives as one considers it from the point of view of human, technology, computational representation, and the physical landscape itself.

This article focuses on a particular mixed-reality game that features schoolchildren using handheld computers to join together into small prides of lions and launch attacks on (purely virtual) impalas that had to be discovered by exploring the physical environment. Although extremely simple in conception, difficulties encountered in the realization of this game highlight the devious problems and complexities that arise in many classes of ubiquitous computing systems.

For example, due to noise and the limits of precision, a sensing technology (such as GPS) may interpret a small huddle of schoolchildren as occupying distinct physical areas, even though from the human perspective they are all clearly co-located, and engaged in a common activity, as dictated by the social grammar of proxemics and f-formations (to borrow two constructs from sociology that characterize how people tend to share physical space).

Such problems are well-known in sensing systems, and a great deal of debate has gone back and forth about how to anticipate and design interactive experiences around  these foibles of the technologies at our disposal.

But this paper takes the unique step of recognizing that these perspectives can be codified, through the mathematical formalism of bigraphs. A series of simple production rules—which furthermore afford an intuitive diagrammatic representation—can then model the comings and goings of people, devices, and computational representations on the physical landscape. The result is a set of rules that allows one to model and formally reason about subtle mismatches between the human and technological perspectives.

While the article does not claim to offer a formal grammar of proxemics, the work certainly hints that such a direction may be possible. With the “Internet of Things” colliding at an ever-accelerating pace with the long-established “Social Expectations of Humans,” the tools and insights offered by this ambitious article may comprise a critical lens through which to reason about (if not reconcile) the critical design mismatches that inevitably arise between them.


Steve Benford, Muffy Calder, Tom Rodden, and Michele Sevegnani. 2016. On Lions, Impala, and Bigraphs: Modelling Interactions in Physical/Virtual Spaces. ACM Trans. Comput.-Hum. Interact. 23, 2, Article 3 (April 2016), 57 pages.