A big target
October 20, 2018 at 2:37 PM by Dr. Drang
While wasting time on YouTube the other night, I came across this Computerphile video (a spinoff of the Numberphile series) on Fitts’s Law and its application to graphical user interfaces. It’s appalling in the number of things it gets wrong, especially with regard to the Mac.
As a warmup, let’s start with the things that are only half wrong.
Contextual menus (about 4:20 in the video)
“You don’t need to make any movement whatsoever. So that is a target that’s really, really easy to get to.”
It is true that contextual menus pop up right where your cursor is, but that doesn’t necessarily mean there’s zero cursor movement involved. The context of a contextual menu—the thing you are interested in operating on with an item from the menu—is the thing under the cursor, e.g., a file icon or a selected text string. While it may be true that the thing of interest is already under the cursor (like selected text right after you’ve made the selection), it often isn’t. And when it isn’t (the usual case when the thing of interest is a file) you have to move the cursor to the target, and in those common cases the contextual menu is no easier to use than any other operation that requires targeting the cursor.
Corners and the X button (5:20)
“If you put a target in the corners of the screen, what you have essentially done there is create a target that is infinitely wide.”
Again, it is absolutely true that the edges of the screen are infinitely wide in a Fitts sense. And the corners are infinitely wide (actually semi-infinite, because they have a definite beginning but no definite end) in two directions, which makes them easier to hit than any of the other edge locations. But the example used for this principle, the X button in Windows, is only in the top right corner of the screen if you’ve expanded the window to full screen. Otherwise, it’s just a normal target.
I’ve noticed that less sophisticated Windows users, and users who typically work in just one app at a time, do tend to keep their windows fully expanded. For these users, the X really is infinite in two directions. But even for these users, how valuable is this? Should the easiest action to accomplish in an app be to quit it? Maybe for some apps, but not in general.1
At this point, Dr. Wiseman goes off the rails, saying things about the Mac user interface that are just plain wrong. The errors come on so rapidly and are so intertwined that it’s hard to separate them.
The Mac close box (6:00)
“Then I think Apple brought it [the X button] down and made it into a circle, so they made the target from being infinitely massive to a tiny little circle… which is kind of silly of them.”
Now you see what set me off, don’t you?
- The clear implication is that Apple took Microsoft’s wonderful X button and ruined it by making it smaller. Surely a researcher in Human Computer Interaction knows that the Mac came before Windows, so why suggest the opposite?
Maybe she’s not implying Windows came first. Maybe she means Apple ruined the infinitely massive X button Xerox used in the Alto or Star. Nope.
(Image from Prosthetic Knowledge.)
- As anyone familiar with Apple GUI history knows, the current circular close button evolved from its own earlier square close box. It wasn’t shrunken down from a significantly larger interface widget.
- Even if Apple were to expand its close button to fill the corner of the window, it still couldn’t be put in the corner of the screen because the top of a Mac screen is taken up by the menu bar. The menus, therefore, which are accessed repeatedly during normal use of an app, are infinitely large in one dimension. This is not a coincidence. Apple deliberately designed the user interface this way to take advantage of Fitts’s Law for common actions. How do I know this? Because back in the 80s when I started using a Mac, you couldn’t read an article on its user interface that didn’t mention Fitts’s law and the menu bar. Read anything by Bruce Tognazzi or Jef Raskin.
- Quitting (or closing a window—we’ll get to that in a bit) is a destructive action. Apple didn’t think it was a good idea to make destructive actions the easiest ones. Dr. Wiseman may disagree, but it’s wrong to suggest Apple was being thoughtless or silly.
- The close button on a Mac is not the same as the X button on Windows. While there are some exceptions (single-window apps), the close button typically closes the window without quitting the app.
- The close button on a Mac is, of course not in the upper right corner of a window, it’s in the upper left. This is more an indication of laziness (or ignorance) on the part of the video editor than a user interface issue, but I couldn’t resist mentioning it.
One of the things Mac users pointed out when Windows came out (apart from all the copying) was that Microsoft’s decision to attach its menus to the app windows meant that its users couldn’t take advantage of Fitt’s Law when accessing menu commands. I’ve often wondered whether the enormous toolbars so common to Windows apps nowadays are an attempt to make up for that.
And Apple does allow its users to take advantage of the infinite Fitts size of corners for quick actions, but they are limited to system-wide actions (since the screen corners aren’t associated with any particular app) that aren’t destructive.
You can fling the pointer into a corner to perform any of these actions—no need to click—but nothing bad happens if the pointer wanders into a corner by accident.
The original Mac/Lisa interface designers spent a lot of time thinking about Fitts’s Law and other interaction matters. That we’re still using most of what they came up with three and half decades later is strong evidence that they knew what they were doing.2
