GUI, VUI — Huey, Dewey, and Louie!
What's the difference?

If you're a Windows or Macintosh user, you're already familiar with a GUI (say "gooey"), or Graphical User Interface. That's how Web pages, Windows, and Macintosh present information to you: by filling your screen with a collection of graphical and visual elements you can physically interact with to get things done.

And, if you've ever had a conversation, you've already used a VUI (say "vooey"), or Voice User Interface—you've used your voice to communicate, interface, and get things done.

But have you ever thought about just how different these worlds are, and how designing for them can involve much different skills, tasks, and goals? Think for a moment about taking your grocery shopping list with you as you head for the supermarket. It's all right there in front of you, and chances are you'll glance at it several times for reference during your shopping trip. Now imagine if you simply heard someone tell you a complex shopping list, before you went to the market. You'd be hard pressed to come home with everything on that list, in correct sizes and amounts!

And that's one of the biggest differences in designing and building GUI vs. VUI interactions: in a GUI, it stays there in front of you and you can visually refer to it as needed. In a VUI, everything happens in a sequential, one-at-a-time fashion and once it's presented, it's gone. GUIs typically require three main tasks of users:

1. Perceive (which in this case means "see")
2. Interpret (figure out what the interface is telling you)
3. Act (decide what you want to do about it)

VUIs ask all of that of their users, but because VUIs are sequential, they also fit in a crucial step before the user can act:

1. Perceive (which in this case means "hear")
2. Remember
3. Interpret (figure out what the interface is telling you)
4. Act (decide what you want to do—in this case, say—about it)

More than you ever wanted to know about GUI and VUI (not to mention Huey, Dewey, and Louie)? That's okay, the important thing to remember is that they are different, they work differently, they're designed differently, and they take complementary but different skill sets. If you would like to know more, take a look at recent article Matt Prather prepared on the subject for Rensselaer Polytechnic Institute; it gives a good capsule description of the differences between GUIs and VUIs.