I read another Slashdot discussion vilifying the user interfaces for GNOME 3 and Unity. Personally, the new interface is growing on me. Since I just finished the book Psychology of Everyday Things, I wondered how it applies. So with five minutes contemplation, I came up with visibility and gulf of evaluation.

Principle of Visibility
A person has to know what they can do. Visibility tells the designer to make possible options visible. You won't know what you can't see.

Okay, Unity starts up with a large empty area, a gray bar at the top, and some pictures on the left side. What now? All of the geeks immediately said push the icons. And there lies the problem. Notice that our imaginary geek called them icons. He knows that they are and what they do. To him, the next action is visible.

Our imaginary geek has knowledge in the head - he knows what those pictures are and what actions they afford. Other people do not have this knowledge. The innate actions are not visible.

Okay, for the Slashdot crowd, this is a pretty poor example. Anyone discussing user interfaces on Slashdot knows about icons. Do they know that right clicking brings up a menu? Or that you can create your own menus, effectively making drawers? Where do you go to look at everything installed? Finding these answers means fumbling around the interface. I'm not getting work done while I'm fumbling.

Unity relies on knowledge in the head. You have to know certain things for Unity to be useful. That violates the principle of visibility. A menu puts knowledge in the world. You see all of the choices right in front of you without any extra knowledge. Knowledge in the world is easier to learn.

The Unity and GNOME developers are right, though - knowledge in the head is faster. Once I know the tricks, Unity is more efficient than the old menu structure. The problem is how to move people from knowledge in the world to knowledge in the head. Doing that by fiat leads to revolt.

Big Icons
Unity's icons are way too large. No, I am not being hypocritical. For one single icon, bigger is more visible. When I'm exploring 200 for something that looks interesting, I want more options. Bigger icons leave less room. Now I have to scroll or page through the options. To compare options, I have to remember information about what I saw two screens ago. Unity make me memorize things.

See - the interface makes me do more work. That's terrible. A computer is supposed to help. Adding tedious memorization does not help. The interface steals my time and energy.

Gulf of Evaluation
This is pretty easy to explain - Unity is SLOW. It has a noticeable time lag between pressing the Dash key and being to type into the search box. Shoot, randomly, the search box doesn't have focus. I hit the Dash key, start typing the program name, and pow - nothing. I expected to see the icon for my program. Instead, Unity lost my typing and I have to start over again.

As we perform actions, people check the results. Did this action move me closer to the ultimate goal? That is evaluation. The time between performing an action and seeing the results is the gulf of evaluation. We call larger gulfs interruptions. It's rude to interrupt, even for a computer.

With the user interface, we want to keep this gulf very, very small. Your action should have an immediate, verifiable consequence. Unity fails when it takes too long displaying the Dash.

Thoughts?
Judging user interfaces is like judging art. Everyone has different tastes. I memorize commands easier than symbols (icons). For me, GNOME Do was perfection. That most definitely affects my perception of Unity. We'll have to see where Unity goes next...