Usability implications of ocular-kinesthetic dissonance
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The Simpsons
Fitts’ Law is a conceptually simple prediction model for explaining the ease of acquiring an interface target as a function of the target’s size and distance from the users’ starting point. Simply summarized as “bigger and closer is better,” its wide application has generated much of Web 2.0′s childish, playschool look. A striking example of a design that pays heed to Fitts’ Law is the Vimeo registration form, which includes enormous input fields, far larger than are typically seen on other sites.
Defining a limit to usable sizes
Good news dude! 3″ is enough for the average user!
If a login form is the most important UI component on a page, shouldn’t we make it bigger and bigger and BIGGER? Fitts’ Law prescribes large interface components, but there are some factors that cause diminishing returns. One is information density – big buttons are nice, but not if they’re the only thing on the page. Another often overlooked limiting factor is the user’s field of vision.
Google wisely leaves most of the page unused for its form field and input.
The eye’s focal width on a page or screen is roughly 3 inches (the fovea centralis provides a sharp field of view of 2 degrees). That’s all we can clearly see in a single instant. Our eyes actually flicker around constantly, taking many images with a surrounding blurry field (about 24 per second), which our brain compiles into a larger image of the world. So an ideal visual “object” measures roughly 3″ or smaller – something we can literally take in at a glance. As the size of a visual object increases beyond 3″, the user’s visual, physical, and mental effort increases. At even larger sizes the object loses its distinction and risks becoming a background/field instead of a foreground/object. Other visual indicators factor into this consideration (color, pattern recognition, borders, etc.), but I believe that usability rises, plateaus, and then declines as visual objects increase in size.
You can see an excellent example of an overzealous application of Fitts’ Law on the Web 2.0 job site Krop. The search field is so large (especially on lower-resolution monitors) that it reads as a non-functional color field rather than a form input for some users. I only noticed it after browsing the site and thinking “Gee, don’t job sites normally include a search box?”
Your user is a blind Cyclops
Remember the story of Jason and the Cyclops, who despite his awesome size was cruel and quick, always scanning the ground for prey (sounds like a MySpace user, no?) Jason’s initial encounter with the Cyclops did not go well: prefiguring Star Trek’s red shirts, a handful of Argonauts became a quick meal for the Cyclops. Captured and scheduled for the stew pot, Jason’s crew hoists a burning beam from the Cyclops’ cooking fire and – POIK – stick it in his single eye. Blinded, the Cyclops searches flails about for his prisoners. The Argonauts finally escape by covering themselves with sheepskins and crawl beneath his groping hands, impersonating his flock of sheep.
In addition to the ancient lesson of not going toe to toe with one-eyed giants, the story also provides a gruesome depiction of user error: blinded and disoriented, the Cyclops is forced to downgrade from his preferred interaction method (visual) to a less effective kinesthetic method. The Cyclops acclimates to an alien sensory landscape by relying on preexisting conceptual patterns to facilitate his decision making process: “sheep are small and feel sheepish, therefore these things must be sheep and not tricksy Argonauts.”
Until users stop using browsers in favor of personal homepages and feed readers, they’ll have to contend with a perpetual learning curve on myriad evolving sites and internet applications. A valuable tool for accelerating this curve is a reliance on patterns and scanning. When users scan interfaces, they use quick appraisals to efficiently assign expectations to interface objects. It is critical to balance usability concepts like Fitts’ Law with approachability concepts like easy scanning and adherence to expectations. An Argonaut should not look like a sheep, no matter how warm and soft it may seem.
If your visual objects are too large, they’ll be improperly scanned
The Krop search field provides a simple example of the complications that result from overemphasis of a single usability concept. Form text inputs are already at a disadvantage because they are visually bald interface objects – it’s not easy to display “space.” A quick does of elephantitis (and in Krop’s case, a subtle gradient style commonly used in backgrounds) pushes that blank field out of the user’s “object” pattern set and into the background.
When designing for users, remember the new users who are so critical for any increasingly popular interface: not quite blind but hampered enough by hurry, worry, and ill-conceived design that their behavior becomes, to some degree, cyclopean.
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