Gorilla Arm

While doing some research, I accidentally stumbled onto the Wikipedia entry for Gesture Recognition, an entry that, amazingly, I’d never seen before, despite days and days of research for Designing Gestural Interfaces. Buried in the entry is a great name for a condition that poorly-designed gestural interfaces can cause: gorilla arm. Although I was certainly aware of the circumstances that cause gorilla arm, I didn’t know the condition had such a great name. I’d never heard it used before, but it makes absolute sense and a quick Google search reveals it is everywhere. Not sure how I missed it, but oh well. Learn something new every day.

In case you’ve never heard the term either or want to know more, here’s the entry:

“Gorilla arm” was a side-effect that destroyed vertically-oriented touch-screens as a mainstream input technology despite a promising start in the early 1980s.

Designers of touch-menu systems failed to notice that humans aren’t designed to hold their arms in front of their faces making small motions. After more than a very few selections, the arm begins to feel sore, cramped, and oversized—the operator looks like a gorilla while using the touch screen and feels like one afterwards. This is now considered a classic cautionary tale to human-factors designers; “Remember the gorilla arm!” is shorthand for “How is this going to fly in real use?”.

Gorilla arm is not a problem for specialist short-term-use uses, since they only involve brief interactions which do not last long enough to cause gorilla arm.

Now, I don’t particularly agree with the first sentence here. I doubt it was an ergonomic challenge like gorilla arm that sank vertical touchscreen displays in the early 1980s; more likely, it was the fact the technology was fairly primitive then (see: HP 150) and would have been hugely expensive. They are still expensive now. But the rest of the section seems accurate, and is a classic problem with gestural interfaces.

Rupert Goodwins at ZDnet traces the term to the 1970s, to people using light pens on vertical monitors.

Light pens had a lot of things going for them. They were simple, accurate and didn’t need much software or modifications to the computer to make them work—all important factors in the days of tiny RAM and expensive processors. Manufacturers and software designers loved them.

But there was one small snag. The human arm—remember humans?—isn’t designed to be held horizontally away from the body for any length of time while making tiny, precise movements. Tasks that took any time to complete, including navigating through menus, soon resulted in aching muscles, stiffness and a swollen feeling—gorilla arm.

Telegraph operators used to get a similar condition called glass arm from bashing badly-positioned morse keys all day, but they’d long gone by the time computers turned up so nobody remembered. Technology’s like that.

So beware the gorilla arm. As Jonathan Brill rightly points out, CES was full of it, as are, frankly, Oblong’s g-speak and HP’s Touchsmart. For more on this topic, I recommend Rob Tannen’s series on Ergonomics for Interaction Designers and the 2003 paper A Procedure For Developing Intuitive And Ergonomic Gesture Interfaces For Man-Machine Interaction (pdf).