Introducing the scroll wheel to web applications

At my company we've been starting our interaction design work by defining an interaction vocabulary. The vocabulary is just a list of verbs--click, drag, drop, hover, keypress--that are meaningful in our application, along with some notes about what each verb "means." (If you want to get more programmatic, you could say we start with events we'll "listen" for.)

This is nothing new [1]; it's just a slightly different starting point for us. [2] The point of mentioning this is to say that we've been deliberately ignoring scroll wheel events.

The scroll wheel is that nearly ubiquitous rolly thing near your index finger tip that makes the page scroll up and down. There are some variations--the tilt wheel and click scroll wheel--but the basic up-and-down scroll wheel is the most common. [3]

Anyway I've been thinking lately that maybe we should be using the scroll wheel. [4,5] It's always been a kind of secondary input--more of an accelerator than anything else. But it has some nice features; for example, once you have focus using the scroll wheel doesn't require target acquisition.

So, looking for inspiration, I tracked down some interesting examples of interaction design where the scroll wheel is a prominent (and sometimes the only) input mode:

• At ShopComposition you can slide through the product line using the scroll wheel. (It's one of those link-resistant Flash site, so you'll have to select a category, then view the full product line.)
• The Nagaoka Institue of Design Gallery has a slick scroll-wheel driven UI. In fact, you can roll through the people and their works without clicking anything.
• Yahoo Maps (beta) supports scroll wheel zooming. The lag between scrolling and refreshing the map is understandable, but a bit distracting.
• The Feature Bob Invented is a nice little story about how an little-known Powerpoint feature (scrolling through slides using the scroll wheel) became an actual feature in Office 12. (This is still scroll-wheel-as-accelerator stuff, but it's interesting nonetheless.)

The scroll wheel has it's downsides--it's one dimensional and favours speed over accuracy. It can also be confusing; depending on where the focus is the scroll wheel can have different behaviours (e.g. scrolling a window vs. scrolling through menu options). Of course, 10 years ago right click was pretty inconsistent. So maybe some scroll wheel conventions that are more nuanced than mere scroll bar manipulation will emerge. In the meantime, it's fun to experiment.

[1] See About Face, Chapter 21
[2] Especially for web applications. One of the things that defines "Web 1.0", if you will, is the impoverished interaction vocabulary. Click was the main verb, and it always meant the same thing--turn the page.
[3] Unless you're on a Mac.
[4] Yeah, I've been reading David Foster Wallace. More on that later.
[5] All of the examples here are Flash. From what I've read, JavaScript scroll wheel events aren't consistent across browsers, which would make an Ajax implementation kind of dodgy. That will probably change in a year or two.