After reading chapters 1 & 2 of Chris Crawford's The Art of Interactive Design & Bret Victor's A Brief Rant on the Future of Interaction Design I can see why it is difficult to concretely define interaction. I agree with Crawford: "many things commonly held to be interactive are not." But I also believe the perception of what is interactive is generational, particularly because of the injection of technology that was previously only science-fiction. (the pictures of the old game carpet come to mind – would anyone of the iPhone generation say that a toy/carpet is 'interactive'?)
How would you define physical interaction? What makes for good physical interaction?
I agree with many of the points of both writers. I see physical interaction as a two-way communication involving some type of somatic component where things affect and respond to each other in a meaningful way. In an ideal interaction, you wouldn't need to read a manual to understand what to do or how to interpret the response. Your life experiences are all the training you need. Physical interactions should take advantage of the diversity of human tools of manipulation and understanding (the five senses) when possible. Two-way feedback is important.
My partner is a classical pianist (in his free time), and more than anyone I'm sure he understands the importance and complexity of tactile perception. (Sidenote: If I try to play the piano, it causes puppies to die.) Interestingly, he has an extreme dislike for the iPad but can't always articulate quite why. His most common answer: "it just feels wrong." But why?
Pictures Under Glass sacrifice all the tactile richness of working with our hands, offering instead a hokey visual facade.
Bret Victor's Pictures Under Glass idea suddenly made my partner's dislike for iPad make sense. The piano provides significantly more feedback than iPad.
Example of digital technology that is not interactive
It's hard to argue that the MTA next train/spoiler alert electronic signs aren't useful. But you don't need to interact with the signs; they happily post the time regardless if anyone is in the station. Certainly there is some interaction going on between computers, but it requires no human viewer to function.
Following Crawford's definition of interaction: you're not interacting with the sign, you are reacting. It's not as though the sign has the ability to notice that you're annoyed because of the 23 minute wait for the L train and therefore speed up the train arrival.