What is interaction?

Defining physical interaction

Chris Crawford defines interaction as “a cyclic process in which two actors alternatively listen, think, and speak.” I think that that definition works well for physical interaction, except that I’d replace the terms “listen” and “speak” with “sense” and “respond”, respectively. Although Crawford uses “listen” and “speak” metaphorically, I think that “sense” and “respond” are a little clearer because they suggest a wide variety of inputs and outputs that translate physical phenomena into analog/digital electical signals and vice versa.

Some examples of physical sensing and responding:


  • Pressure
  • Temperature
  • Sound
  • Light
  • Distance (Ultrasound)
  • Speed
  • Acceleration
  • Orientation
  • Stretching
  • Moisture


  • Light
  • Sound
  • Movement
  • Heat
  • Cold
  • Pressure
  • Vibration
  • Texture

What makes for good physical interaction?

I think that Crawford’s thoughts about “high” vs. “low” interactivity are on point here. It’s not enough to just listen, think, and respond - each step has to be done well. Good physical interaction requires a work or piece of technology to:

  1. Sense accurately
  2. Process what it senses in an interesting or non-trivial way
  3. Respond in a way that is comprehensible and communicates meaning

Bret Victor’s comments about moving beyond visual interfaces are also relevant here. Good physical interaction should try to use other human senses as well, such as texture, temperature, hearing, etc. Good physical interaction should be, well, physical.

Examples of non-interactive digital technology

One of my favorite works that involves digital technology that would not be considered interactive is Julien Maire’s Digit, a performance piece that makes use of tiny, hidden printers to create the illusion that the artist is producing printed text simply by sliding his finger across a piece of paper. The printer system isn’t really interactive according to the definition above; it’s more of a tool that translates the artist’s movement into text.

Jürg Lehni’s drawing machines (and most drawing machines in general) are also examples of non-interactive digital technology. They translate images or text into physical motion - communication is one-way from human to machine.