Like many other runners, I like to listen to my music while training. Even with a playlist of running music, I often want to change the currently playing track. There are currently two popular options of doing this: using the device itself, or using a headphone remote. My ubiquitous computing project from last Spring explores a third option: imagine if your shoes had built-in accelerometers that allowed you to skip mid-stride to change tracks.

The most obvious way to change tracks is directly through the music player, but operating a touch screen while running is pretty annoying. A much better way of changing tracks is by using a button attached to a pair of headphones, but finding it, and then double clicking it is often a frustrating experience. Some clicks don't get registered, so one often ends up triple-clicking, which skips back a track. My project explores a novel way of changing tracks: mid-stride skip. This gesture is detected by having an accelerometer in each shoe which tracks your running patterns and detects when you perform the skip gesture. In addition to being useful, this running gesture makes an otherwise monotonous activity more varied and enjoyable.

I prototyped the skip-to-skip system with a wii remote attached to the runner's lower leg, as pictured above. A computer is paired to the wiimote, collecting accelerometer data (especially in the axis corresponding to the runner's vertical movement). This communication is established using a wii library from a previous post. The naive algorithm I use for detecting skips works as follows:

1. Find peaks by looking at the 1st derivative (positive slope, negative slope pairs)
2. Discard insignificant peak values (under a threshold)
3. Compute distances between peaks
4. Look at the last 5 distances, and compute the mode. That's the pace.
5. Look for declinations from the pace characteristic of a skip.

Once my gesture recognition code worked reasonably well, I ran a user study to see how people liked this method compared to the touch screen and headphone remote. After a few hitches (including getting kicked out of the Madeira Tecnopolo), I managed to test the prototype with many of my Madeiran classmates (thanks guys!). Most people preferred the skip-to-skip method over both the direct smartphone and headphone remote methods, which is promising.

For more details on this project, check out the paper that Vassilis Kostakos and I will present at Ubicomp 2010 in Copenhagen. If you're interested in the source code, it's located on github.

Update: here's the poster. The font-size is scary huge on A0!