Matthew Kaney at ITP

Blog 1: What is physical interaction?

Physical Computing


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In The Art of Interactive Design, Chris Crawford defines interaction as the process through which two actors take turns listening, thinking, and speaking, like in a conversation. After defining his terms, he explains himself with some nice examples: computers are interactive, books and movies aren’t; dancing with another person is interactive, dancing to music is not; live performances can be interactive, but are hardly ever interestingly so. This definition is pretty cut and dried, and it makes a lot of sense, especially given Crawford’s bias toward computer interfaces. If one is imagining information conveyed through sight or sound (most computer output, to be sure), it’s easy to think of discrete moments of communication back and forth with processing time in between. We imagine a horror movie viewer shouting at the unlistening screen and appreciate our interactive media all the more.

Unfortunately, once we start considering touch, everything goes murky. I can shout at a movie screen to no effect, but if I touch it, things happen. The screen will move, or resist, or transform its shape. This process of action and response sounds kind of like our interaction cycle—are all physical objects interactive?

Crawford has no patience with this line of reasoning. No, such actions don’t count. In his definition, the actors must be “purposeful”—a deceptively philosophical concept used here as shorthand for “a computer.” He dismisses the refrigerator light switch as a trivially simple interactive mechanism, before promptly changing the subject. Left unsaid: is there a machine sufficiently complex to count as interactive? A piano? A typewriter? A mechanical calculator? Do any of these machines “think” enough to really interact? In this light, Bret Victor’s “Brief Rant on the Future of Interaction Design” seems relevant. Victor is a champion of physical objects. He admires the way we manipulate them, the subtle information their weights, temperatures, textures and so on impart. Physical objects can be acted upon, and they can communicate back, but Victor never actually uses the i-word when describing hammers or jar lids.

My interpretation is that both writers are driving at the same continuum from opposite ends. On the one end are simple physical objects, which I would call reactive, and on the other are full interactive systems. And what separates the two? Nothing specific, I’d argue, especially not Crawford’s requirement that an interactive agent think or act purposely.

So, what defines interaction, then?

Most everything is reactive, meaning that it behaves (broadly speaking) like an interactive object. A hammer may not interact, strictly speaking, but it will react in specific ways, which is almost as interesting. However, if we must propose an arbitrary distinction, I believe it is this: interactivity is not determined by how elaborate an actor’s thinking ability is, but rather by how much novelty the actor injects into the interaction. We don’t think of a rock as interactive because when we move it, it moves as expected, no more or no less. The simplest interactive system may therefore be a handful of dice. Roll the dice, and the result is unexpected, forcing us to reevaluate and keeping us engaged. A system can be sophisticated or not, predictable or not, but as long as each new round adds new information, we (the humans) don’t get bored, and the system has successfully interacted.

At the same time, we shouldn’t discount merely reactive objects. As Bret Victor points out, there’s a wealth of information to be found in the ways that physical controls react to human touch. Ideally, the physical interactions we design should blend both ends of the spectrum. Small, reactive details make things more comfortable and understandable, and a broad interactive design keeps the process interesting. The “pictures under glass” that Victor criticizes are great case studies of a design that’s interactive, but insufficiently reactive.

Of course, a designed object can also be reactive instead of interactive. The computer mouse is often cited as a pinnacle of interaction, but I contend that it is less interactive (by my explanation of Crawford’s definition) than purely reactive. The mouse rarely gives the user new information. Rather, it does what it’s told, accurately, but boringly. If the person and the mouse are having a conversation, that conversation is pretty one-sided.

In light of this idea, I thought back to an electronic artwork I read about years ago, Rafael Lozano-Hemmer’s Pulse Room. This piece (where a user’s pulse controls the flickering of a lightbulb in a large array) still attracts me for the reasons it did then—it’s impressive, yet elegant, and so simple to use. However, I now wonder whether it should really be considered interactive. Crawford would probably say it was, but ultimately, it responds in exactly one way to any type of input. It’s a good response, to be sure, but when designing interactions, I feel we could stretch further. How do we respond in interesting ways that keep our users engaged? That, to me, is the fundamental question of interaction design.


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