Apple Breaks The Consistency Rule

Interaction Design February 06, 2008

My friend Elliott informed me that there's a discrepancy between the MacBook Air multi-touch interface vs. the iPhone interface and it's quite fascinating.

A major part of Apple's Human Interface Guidelines (Found Here) is Consistency. That is, ensuring that all applications for the Mac platform are consistent with each other both in functionality and interface design. Well that makes sense - users will get used to a specific functionality and should expect to see it all over the place (for example, expecting a program's preferences to be under the right button in the menu bar).

Consistency is a major player in the Mental Model: Goal + Action = Expectation. If the action is not what it should be, then the end result is not expected - and this causes confusion.

Generally, Apple strives to create interface design solutions that mimic the real world - especially when it comes to the iPhone, the first device that actually uses your hand as input rather than an input device.

Okay, okay - so what did they do to break this consistency rule?

On the iPhone, when browsing photos, you can flick left to go to the next photo (right). You flick right to go backwards - just as you would if you were flipping through a book of photos. This, of course, mimics the real world and makes perfect sense as you use the iPhone.

However, using the Macbook Air's multi-touch pad with a program like Preview actually does the opposite. That is, if you move right on the trackpad, the image moves left! Take a look at the Video Here and then try using the iPhone. You'll notice that as the user moves left on the track pad, the image appears to move right, because he's moving the viewing plane left.

So here's the deal. There are two ways we can interact with these "film strips" of images. Either we move the strip, or we move the viewing plane. On the iPhone, we are moving the strip when we touch the screen. We grab a photo and drag it right and it moves right. But on the Macbook Air, we are moving the viewing plane, so our actions have opposite effects.

Anywho. This goes against the consistency principle because it doesn't match up with the iPhone interface. So the question is, which is the best way? Moving right on the trackpad will take you to the next image in Preview. Moving right on the iPhone will take you to the previous image.

The truth is, they're actually both correct. When you flip through a photo album in the real world, you move the page left to go forward. That makes sense. But also notice that when you look around at your world, as you move your head left, the image slides right over your retinas. So this, too, mimicks the real world. The difference is touch vs. viewing plane. Context is important.

But it's my opinion that the MacBook Air interface should be like the iPhone. When you click and drag stuff on the display, they move in the direction of your finger. This should be consistent throughout everything.

Clearly we need to be thinking about what exactly we're mimicking in these new multi-touch gestures. Are we doing something like the real world (a la iPhone) or are we doing something more computer-y? Perhaps we need third-party multi-touch human interface guidelines.

Other Interaction Design Posts