About dysclicksia

When doing interaction design, mouse clicks or finger touches seem like very natural and basic actions, but there are more points to think about than you might expect.

Distinguishing single click and double click

Because there are generally no visual hints telling you which UI elements respond to a single click, which respond to a double click, or whether the same element responds differently to single and double clicks, users generally have to memorize this. It is only that, after some time, people become used to it and therefore mostly stop being conscious of it.

In a web browser, if you single-click blue underlined text, another page opens. But in desktop Explorer (Windows) or Finder (Mac), you have to double-click to open a file. Yet even on that same desktop, icons on the taskbar (Windows) or Dock (Mac) open with a single click.

Behavior that changes depending on the situation

In some contexts, even on the same desktop and in the same app, behavior changes depending on the situation, so sometimes you have to distinguish not only between single click and double click, but also between single click and single click. What do I mean by that? For example, in Explorer (Windows) or Finder (Mac), a single click selects a file. But if you single-click an already selected file again—in other words, if you single-click twice—it switches into rename-file mode.

Wait a second. But if you single-click twice, isn’t that a double click? No. It is a double click only if you click twice “fast enough.” If you click twice slowly, or if you move the mouse “enough” between the first and second click, then it is not a double click. We will look at this issue in more detail in a moment.

Interaction methods that change over time

Even within the same operating system, interaction methods can change over time.

In the late 1990s, Windows 98 introduced the “Active Desktop,” which integrated Windows and the browser (Internet Explorer), and in the process almost eliminated double-clicking within Windows itself. In Korean, saying that it integrated Explorer (strictly speaking, the “desktop” is actually part of Explorer) and Internet Explorer can sound a bit strange, but in English it was an integration of “Explorer” and “Internet Explorer,” so it does not sound strange. Of course, this “integration” also made the controversy over antitrust violations more serious, but that’s a story for another time.

In the mid-2000s, the opposite happened: as the concept of so-called “Rich Internet Application” became fashionable, the web began imitating desktop UI, and as a result interfaces making use of double-click or right-click rapidly increased on the web as well. RIA was a marketing term created by a company called Macromedia (later acquired by Adobe) to promote its product “Flex.” At the time it became hugely popular together with the Web 2.0 boom, but now it has become a term that is hardly used anymore (the fact that “RIA” is still used in the web accessibility standard Accessible RIA is a slight exception). Looking back, the Flash+Flex combination had many points where it diverged from web standards (dependence on a specific company, black-boxness, lack of interoperability with other web standards, etc.), so it may seem a bit puzzling why it did so well at the time, but there were reasons for that. That story too, another time.

For these reasons, as desktops came to work a bit like the web and the web came to work a bit like the desktop, it became even harder to memorize where to single-click and where to double-click.

Some people double-click everywhere, including on web links. I suspect they formed a habit of always double-clicking because it is difficult to memorize which places require a double click and which require a single click. In my observation, they were relatively often older people, and that makes me a bit sad, because the older one is, the more that action of clicking the same spot twice in a row within a short time and without movement—a double click—seems as though it would place more strain on the joints.

Declining visibility

As the web began imitating the desktop, the convention of marking links as blue underlined text also rapidly disappeared, and visibility—or discoverability—dropped sharply.

In the early 2010s, flat design began to come into fashion. Apple joined in as well in 2013, declaring its break from skeuomorphism and adopting an extreme design that removed even shadows from UI elements. There were probably several reasons for the popularity of minimal-flat design in this period, but I think one factor was that, as the diversity of device form factors increased explosively (mobile phones of various sizes, tablets, landscape and portrait modes, desktops, etc.), minimal, geometric design also became almost unavoidable. (The reason I myself experimented with flat design based on the card metaphor around 2007–2008 was the same.)

As the iPhone’s multi-touch interface combined with the excessive minimal design of the early 2010s, visibility declined even further, and now users, before even distinguishing between single click and double click, also have to perform the task of finding where to click.

Contrary to a common misunderstanding, shadows have nothing to do with skeuomorphism, and because they are a very important design element that can make excellent use of universal human visual-perception mechanisms, I think this decision was a major mistake by Apple. Google’s Material Design used shadows as an important element from the very beginning, and I think that was the right choice. Fortunately, shadows are gradually returning again to Apple’s design as well. That story too, another time.

Single click, double click, drag

Once you have found where to click and also figured out whether it is a single click or a double click, it is time to carry it out.

Let us assume you are doing a double click. If we call the action of pressing the button D, the action of releasing it U, and movement m, then a double click is DUDU. But because human fingers are not as precise as machines, a short movement can slip in between each action. In other words, you want to do DUDU, but in reality cases arise such as DmUDU, DUmDU, DmUmDU, and so on.

If someone has a motor impairment, this is a problem they experience more frequently. Jef Raskin calls this dysclicksia in The Humane Interface. It is not the name of a real disorder; apparently it is a term coined by Pam Martin in 1997. From the perspective of universal design, if you think about it, anyone can experience it in many situations even without a severe motor impairment: mild tremors, hand shaking caused by diabetes, using a laptop while sitting on a moving subway train, and so on.

The problem is that DmU is, by definition, not a click but a drag (because you moved while holding the button down and then released it), and DUmDU is two single clicks (because you moved the mouse between the first and second click); and even if it is DUDU, if enough time passes between the first DU and the second DU, then again it is just two single clicks.

That is why, in most operating systems, even if there is a short m between D and U or a short m between DU and DU, it will still be judged as a double click if the m was short enough and the timing was fast enough. If you open the operating system’s accessibility settings screen, you can see all sorts of parameters related to click or double-click behavior.

If it is a touch screen rather than a mouse, even more correction is needed. In particular, this is because the area where a finger touches the screen is far too large compared with the pointed tip of a mouse cursor; because a finger is not transparent, it visually obscures the touch point; because humans perceive the touch point differently depending on the angle from which they are looking at the screen (which is why, if I try to touch a phone someone else is holding, I end up touching the wrong place); and because, unlike a mouse stably attached to the desk surface, a finger is floating in the air.

In the end, users provide ambiguous gestures between double click, drag, and two single clicks more frequently than they themselves realize, and computers deploy all kinds of heuristics to interpret those ambiguous gestures as diligently as possible.

Conclusion

If you take these points into account when doing interaction design, you can create a more pleasant interface. For example, because two single clicks, a double click, and dragging are gestures whose distinctions are less clear-cut than one might think, it is best, whenever possible, to avoid designs in which mistakes between those three actions are likely to cause problems.