Let’s briefly talk about the iPod, because this is another great example of body-thinking.

With the early iPods, the wheel on them moved mechanically, so you’d discover what to do just by playing. But on later models, the wheel didn’t move—you had to slide your finger along it. How to design it to indicate that.

The answer takes into account affordances. When you see a coffee mug, you don’t just see its colour, its shape, and the fact the handle is on the left, you see the possibilities of using it: immediately you see the mug, you left hand prepares to pick it up. Affordances are the possibilities of use, and they take a route into the brain as fast as colour or shape.

The scrollwheel needs to visually advertise the fact that you put your fingers on it, grip, and pull round.

Normally we use rubber for grips, and the rubber goes grey because people have grubby fingers—or you make it grey to begin with so dirt doesn’t show up.

The iPod designers made the wheel grey to visually advertise the affordance of gripping and rubbing along. All they had to do was make you touch it once, and then the response of the screen interface would take over and help you learn the rest.

Your body naturally does the right thing, then your brain takes over. It’s a neat solution.

Matt Webb, S&W, posted 2006-07-14 (talk on 2006-07-13)