A recent blog post on MSDN discussing the usability process behind the new Microsoft Office 12 “ribbon” used to present function icons in the interface described how they learned from observation that users could scan the icons more quickly when the icons are not all the same size. But not everyone thinks (based on their intuition) that different sized icons are a good idea.

I (Jensen Harris, the blog author) was reading a blog entry of someone who was kind of critical and dismissive about what we’re doing and our designs. One of his criticisms was “how bad the usability of the Ribbon would be because it’s got icons scattered all over of various sizes.” What we’ve learned is actually the opposite. People can scan disparate patterns more easily than homogenous patterns. When we use more toolbar-like layouts–a bunch of equally-spaced, equally-sized buttons, people scan them less quickly than when each chunk has a memorable layout. So we actually try explicitly to vary the layouts between chunks–it helps people find the thing they’re looking for more quickly.

This is a great example of how we are re-discovering some basic perceptual principles that have been studied psychologists for nearly 100 years: humans (and all insects and animals, for that matter) are designed to perceive change. We notice more quickly when things are different or when they change, and we get perceptually “bored” when things are all the same and never (or rarely) change. We know from software design experience that rows and rows or columns and columns of the same icon in file management UIs offer no scanning advantage, but if just one of those icons differs it seems to literally jump off the page at us. We notice the difference.

It is possible for historical reasons that function icons in toolbars are the same size because is it easier to design and build a toolbar where everything fits together like uniform bricks. It’s more difficult to create a toolbar where all of the pieces are different sizes and must be properly arranged in order to “look right.” Perhaps we have a perceived need for a grid-based system because it is simpler, not because it is better.

Yes, icons do vary in color and content based on the function, so there are differences among the icons already, but a standard icon size introduces a regularity that makes it more difficult to see those differences. Reading researchers have known for a long time that we read LONGER TEXT PASSAGES WRITTEN IN ALL CAPS MORE SLOWLY THAN WE READ PASSAGES WRITTEN WITH BOTH UPPER AND LOWER CASE LETTERS, because the ascenders and descenders provide us with word patterns based on the differences among the letters that we recognize more quickly. All caps letters are uniform rectangles, but a mixture of upper and lower case letters are a sequence of different sizes and shapes. We notice the differences.

Change and difference can occur in more than size, shape, and color; it can also occur over time. Our attention is drawn by things that move. Yes, we can see things when they are stationary, but when something moves it attracts us, it makes us want to look at it. Predatory animals are particularly sensitive to movement, but when the prey remain motionless it is much harder for the hunter to perceive it. Camouflage only works well when you are sitting still. Many animals are equipped with the coloring and instinct to blend in: fawns lay motionless in the dry grasses and stick insects cling motionless to branches. If they move, they become dinner.

We can use these perceptual principles to our advantage: facilitate scanning by using color, shape, and size cues to create memorable patterns, and draw attention with the use of differences, change, and motion. Although it may be easier to build UIs based on a grid pattern, the reality of our perceptual systems (and of the organic world) is that patterns are based on differences not similarities.