Multi-touch Accessibility

A colleague just pinged me about accessibility in our multi-touch tables and how we’d tried to accommodate. Here were my major points:

• The height of the tables are wheelchair accessible and ADA compliant. We realized that someone in a wheelchair might not be able to reach the entire experience from a single vantage point so in the physical installation the experience is accessible from multiple sides. (Side note, this design constraint was a primary factor in driving the projector selection, the size of the table, using mirrors for the projector throw, and the overall form factor.)

• There’s no sound. We just didn’t include any and I wasn’t convinced it was going to substantially add to the experience especially when we have multiple tables installed. We have the added bonus of being an art museum and our patrons generally like quieter experiences in the galleries, unlike a science museum.

• The display is pretty high contrast in design and execution. Things that are touchable are visually bright, everything else visually recedes.

• We also eliminated any modality in the UI which let us also get by with minimal instructions (There are two instructions, one of three words, the other of 6 or 7).

• The magnified area is fairly large, but this was for a few reasons. First, my personal aesthetics (as is most of the UI, anyway. ;) Second, there’s some imprecision in how the table calibrates (we’re undistorting from a fish-eye lens and the camera capture rate isn’t incredibly high) so having a larger active area covers up the imprecision (we’ve introduced enough fudge in the end result that you instantly accept that it feels right). Third, since your fingertip is the point of interaction we designed so you could see around your finger. Fourth, we delay the removal of the magnified area for a few seconds after removing your fingertip so you can remove your finger and still see what you’re looking at. If you put your finger back in about the same location, the magnified area stays visible. (In software, we’re making assumptions that over the refresh period a touch detection within a given distance and velocity of a previous touch is probably the same touch (if a finger is moving quickly, you may not consistently detect it across the full length of travel))

On the whole, with the exception of the height restrictions, I’m finding that when we do pretty good interaction and UI design that it naturally accommodates impaired audiences. I think if you reach a point where you begin to think you need to do something unnatural to reach a broader audience it’s probably a good point to reassess your design anyway to see if you haven’t artifically constrained the experience.