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Wizard Of Oz

Object of Play

In this role-play exercise, two people prototype a machine–human interaction. The user talks to another who is “behind the curtain,” playing the role of the machine. They may use a script to uncover breaking points in an existing design, or improvise to work out a completely new idea.

Number of Players

2, plus observers

Duration of Play

30 minutes or more

How to Play

If a group is testing an existing design, they should prepare a script that outlines the responses and actions that the machine can take. The “wizard” will use this—and only this—to react to the user. For example, a group that is designing an ATM interface would write a script of information presented to the user and the responses that it understands in return.

If a group is improvising, they can just get started. To open the exercise, the two players should be visually separated from each other. This is the “curtain” that keeps them from inadvertently passing cues or other information to each other. They may be separated by a piece of cardboard, or they may simply turn their backs to each other.

The easiest way to play through the exercise is for the user to initiate some task that she wants to accomplish. As the two players play through the experience, they should look for problems, frustration points, or opportunities to do the unexpected. Essentially, the user should challenge the machine, and the machine should stick to what it knows.


This technique’s application has grown beyond voice control, as the “curtain” simultaneously eliminates assumptions about the machine and surfaces what the user wants to do and how she wants to do it.

The technique was pioneered in the 1970s, in the early design and testing of the now-common airport kiosk, and in IBM’s development of the “listening typewriter.” In these cases, the technique is taken even further: the person playing the machine would interpret voice commands from a user and manipulate a prototype of the system accordingly, like the invisible “wizard” in The Wizard of Oz.