I have one big regret about my Rocketbirds Revolution! interview. It was the perfect chance to unpack a pervasive problem with a thoughtful and interested developer. I blew it because I was low on time and didn’t realize he’d be so interested in the issue. This article makes amends for that failure: today I explain a usability problem called interference.

If you’ve ever played a few hours of Halo and then washed them down with Left 4 Dead, you already hate this problem. Say you’ve had your fill of pwning noobs in Blood Gulch, and you think you’ll do some pro bono work and help them through some movies on expert difficulty. Someone manages to spatter a boomer right next to you, so now you’re suddenly blind and delicious. Mowing down all the survivors with friendly fire is somewhat outside the charter, so you back into a convenient corner and reach for the B button to melee.

Nope, that’s melee in Halo, so you reload instead. The eight zombies you were trying to shove nibble 80% of your health, and badly-aimed ballistic help from your allies take care of the rest. You’re still in expert mode, so by the time you’re back on your feet, the director has already dropped a tank on you. You put enough buckshot into the tank to draw aggro, but now you’re low on bullets and high on trouble. The prudent thing is to run backwards to buy some time while you reload, so you reach for the right bumper and mash the left stick down.

Nope, that’s reload in Halo, so now you’ve spun 180 degrees and you’re running backward toward the tank with no ammo. Before you know it, you’ve been kicked from the team for being incompetent and someone has left a nasty user review about you on Xbox Live. By the time you’re done appealing the review and you’ve found a new group, it’s 3:00 a.m., you eventually oversleep for work, get fired, and end up sleeping under a bridge. If only these games had the same buttons!

The problem I’m describing here (ignoring your irresponsible gaming habit) is called interference. You need two things to produce interference: a conflicting pair of task sets and a single context. A task set is just a compact psychology term that describes a set of rules that effect outcomes. When you play a FPS, the task set is literally the control layout. When you sort your laundry, the set is examining and separating light and dark clothing. The context is just where you’re doing the task and the materials you’re using to do it. So you might play your FPS games in the living room on your Xbox 360, and sort your laundry at the Laundromat.

So in the Halo to Left 4 Dead transition, you might have the single context of playing a FPS in your living room. However, because the task sets (control layout) slightly differ between the two games, they come into conflict when you try to switch from one to the other. After you’ve been playing Halo 3 for hours, its task set is pretty tightly bound to the context by short-term learning. That binding gives the Halo 3 task set a competitive edge when you start playing Left 4 Dead 2, even though it’s wrong. The effect is hardly compulsory and can be overcome with a thought, but add a little pressure (say, fifty slavering zombies), and that little nudge is enough to trip you up. It’s no dealbreaker by any stretch, but it is an irritating usability blight that games would be well rid of.

Sadly, you can’t really reconcile the task sets for Halo and Left 4 Dead, because the games have different rules and developers. However, interference can even rear its bothersome head inside a single game, so long as it has conflicting task sets in a single context. That brings us back to Rocketbirds. It’s hardly the only game with interference problems, but it is the only game with a developer who both cares and might actually listen. Here’s the control layout:

The culprit is the Z (action) key. Holding the key makes you run, tapping it while you hold shift fires your weapon, and tapping it in isolation treats Z like a context-sensitive button (i.e. throw switch/call elevator/grab ammo/etc). It’s tempting to compress all those functions onto one button because they’re all conceptually actions. Fewer buttons means more casual-friendly, and more people enjoying your game faster is only good for everyone. However, say you’re exiting an elevator at the top floor. If your task set for moving is ordinarily “hit Z to run”, it conflicts with hitting Z to call the elevator back down. If you try to run as you exit the elevator, you’ll have to make another round trip before you can try exiting it again. You can’t resolve the interference with level design; moving the elevator call button away from the platform only changes the details for how the same problem plays out. You have to split running and context-sensitive actions into two separate keys.

The rule of thumb for identifying interference is to ask yourself, “is there a situation where pressing the right key will give my player the wrong outcome?” Any time the answer is yes, you need another button. You can’t hide mechanical complexity behind control simplicity. It causes more harm than it cures.

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

Tags:   halo · interference · Left 4 Dead · rocketbirds: revolution1 Comment

Trackback to this article.