By Jared M. Spool
Originally published: Jan 10, 2005
In a recent usability test, I once again witnessed something I've seen a hundred times before: a frustrated user claiming he knows exactly what is wrong with the interface he was fighting with. What was his suggestion? "These guys need to make this thing a lot more intuitive. The problem is that this program isn't intuitive enough. It needs to be more intuitive!"
I think he used the I-Word no less than 25 times during the session. His frustration was real and his desire was great. So, why wasn't the interface 'intuitive'? Well, it's probably because it's really, really hard to do.
People Intuit, not Interfaces
To those who police the English language, interfaces can't be intuitive, since they are the behavior side of programs and programs can't intuit anything. When someone is asking for an intuitive interface, what they are really asking for is an interface that they, themselves, can intuit easily. They are really saying, "I want something I find intuitive."
But, I believe that English is an adaptable medium, so it's ok with me if we call a design intuitive. Yet, what does it mean, from a design standpoint, when someone desires a design to be intuitive?
To answer that question, we first have to look at how people understand the design in the first place. To do that, we need to look at the design's knowledge space.
Current and Target Knowledge Points
Imagine a long wall where you'll line up all the users who will use your design. We're going to want to organize the wall, so against the left side, we'll put everyone who knows absolutely nothing about how to use the interface. (Maybe they don't even know how to use a mouse.)
On the right side, we'll put everyone who knows everything there is to know about the design. (That may only be the designers.) We'll organize all the people along the wall by how much they know. If they know only a little, they'll stand closer to the left. The more they know, the closer we put them to the right. (Here is a picture of what our wall might look like: )
You can think of an interface’s knowledge space as a continuum which goes from knowing nothing about the interface and to knowing everything someone could possibly know.
If you're looking at the wall, the distance from the left represents how much any given user knows about the design. For each user, we call this the current knowledge point. That's the amount of knowledge they have when they approach the interface.
There's another point that's of interest to us: the target knowlege point. This point represents how much knowledge the user needs to know to accomplish their objective. Every time a specific user tries to complete a specific task, the current knowledge and target knowledge points become very important to us. (Here you'll see our wall with sample current and target knowledge points marked off: )
For a given user trying to complete a given task with an interface, there are two points in the knowledge space that interest us most. Current Knowledge represents the knowledge the user has when they first approach the interface to complete the task. Target Knowledge is the knowledge the user needs to accomplish the task.
Now, every user will have a different current knowledge point and that point changes as they get more experience. Yet, we've found that, by plotting out different users, we often see very clear clusters–bunches of users that share extremely similar current knowledge.
Working with users in the middle of several of the most important clusters gives design teams a nice place to start. (Using these clusters can help design teams determine which personas to focus on.)
The Knowledge Gap
The distance between current knowledge and target knowledge has a technical name: "The Gap". (Subsequently, an entire chain of clothing stores was named after it!)
The Knowledge Gap is where design happens. We don't need to design to the left of current knowledge point, because it's all stuff the user already knows. And we don't need to design stuff to the right of the target knowledge point, since the user won't be needing that information (for this task, at least). We only need to design the interface for the space in between current knowledge and target knowledge. (See a picture of the Knowledge Gap here: )
The space between the Current Knowledge and Target Knowledge points is called The Knowledge Gap. This is the portion of the knowledge space we're most concerned with when we're designing interfaces.
Users can complete their objective when current knowledge equals target knowledge. There are two ways this can happen. You can train the user, thereby increasing their current knowledge, until they know everything they need to know. Or, you can reduce the knowledge necessary, by making the interface easier, until target knowledge only requires the information the user already has. In fact, most good design involves both: users are trained (through explanatory text and other devices) while the designer reduces complexity, reducing the gap distance from both directions.
The Two Conditions of Intuitive
In our research, we've discovered that there are two conditions
where users will tell you an interface seems 'intuitive' to them. It only takes meeting one of the two conditions to get the user to tell you the design is intuitive. When neither condition is met, the same user will likely complain that the interface feels 'unintuitive'.
Both the current knowledge point and the target knowledge point are identical. When the user walks up to the design, they know everything they need to operate it and complete their objective.
The current knowledge point and the target knowledge point are separate, but the user is completely unaware the design is helping them bridge the gap. The user is being trained, but in a way that seems natural.
The Hotel Phone
Recently, I stayed in a hotel while visiting an old friend. Wanting to call my friend to warn him of my imminent arrival, I approached the phone in my hotel room and lifted the receiver, ready to make my call. Can you guess what button I pressed first?
Chances are you guessed the '9' button. As adults, we learn at an early age that the '9' button will get us an outside line when using a business or hotel phone system. This becomes part of our current knowledge as we travel from phone system to phone system. '9' becomes intuitive, though it isn't innate&we had to learn it somewhere along the way.
Of course, for this hotel, you would've been wrong. The designers of this phone felt that the '8' button was a much better choice. How unintuitive could they be? Everybody knows '9' is far more intuitive!
Because other people had problems with this, there were little signs all over–on the phone, on the wall, on the receiver–that stated you needed to press '8' to get an outside line. I immediately saw these signs and, without really contemplating the design, pressed '8' and the rest of my friend's number.
The signs made '8' seem intuitive by training me without my even realizing it. They narrowed the gap quickly and without the distraction often associated with learning new things.
Had the phone used the '9' button, it would've met condition #1. However, since it had the signs for the '8' button and they worked unobtrusively, it met condition #2.
Making Designs Seem Intuitive
The biggest challenge in making a design seem intuitive to users is learning where the current and target knowledge points are. What do users already know and what do they need to know? To build intuitive interfaces, answering these two questions is critical.
For identifying the user's current knowledge, we favor field studies. Watching potential users, in their own environments, working with their normal set of tools, and facing their daily challenges, gives us tremendous insight in what knowledge they will have and where the upper bounds are. Teams receive a wealth of valuable information with every site visit.
For identifying necessary target knowledge for important tasks, usability testing is a favorite technique of ours. When we sit users in front of a design, the knowledge gap becomes instantly visible. (We've had great success, right after a test, listing out all the knowledge the user needed to acquire during the test. It can be quite revealing!)
Intuitive Doesn't Always Make Sense
Unfortunately, making an interface intuitive often increases development costs dramatically. Reducing target knowledge, particularly for large knowledge gaps, can be a very expensive process, particularly if you have to build complex tools, such as wizards and data auditors.
Anyone who has tried to build a tool that reduces target knowledge knows that they take tremendous work to get right. Is making an interface intuitive worth the investment? Not always.
For example, Amazon makes the process of returning a purchased product fairly intuitive. Once a user finds the (sometimes hidden) magic button on the order form, they have no trouble going through the return process–a multi-step wizard which asks intelligent questions and guides the user through the process of printing a shipping label, determining the shipping costs, and returning the product.
However, in our studies, users have much more difficulty finding a phone number to call Amazon's customer service center. Amazon doesn't want a lot of phone calls from users. They aren't set up to handle the volume of calls and building a complete customer service call center could render their entire operation unprofitable. While it's inconvenient to the user, they'd rather handle the problems through email, which is far more cost effective.
The designers at Amazon have deliberately made the process of calling them very unintuitive to encourage customers to find another way to resolve their problems. (We're not saying this is the right thing for Amazon to do, but their choice does have some sound logic behind it.)
Understanding How Intuitive Works
Once you understand how 'intuitive' works–what makes someone perceive a design to be intuitive–it becomes easier to make the decision as to whether an intuitive design is worth the extra effort. The knowledge your users have when they arrive at the design (current knowledge), what knowledge they'll need to complete their tasks (target knowledge), and what the design needs to do to help them complete the task (the gap) are the key ingredients for making an interface that seems 'intuitive' to your users.