figure 3: in this inversion-problem game,
given an input, Player 1 produces an output, and Player 2 guesses the input.
Player 1
INPUT
Player 2
(t ) output
1, 1 1, 1
(t ) output
1,n 1,n
(t ) output
1, 1 1, 1
(t ) output
2, 1 2, 1
(t ) output
1,n 1,n
(t ) output
2,m 2,m
Players win if/when output = INPUT
2,i
figure 4: in this input-agreement game,
players must determine whether they
have been given the same input.
Player 1
INPUT
1
Player 2
INPUT
2
(t ) output
1, 1 1, 1
(t ) output
2, 1 2, 1
(t ) output
1,n 1,n
=≠
(t ) output
2,m 2,m
=≠
Win if players guess whether INPUT = INPUT
12
input; all they know is that they must
“think like each other” and enter the
same output.
This game structure accomplishes
several goals at once: a good “winning”
strategy for the players is to produce
outputs related to the only thing they
have in common—the input; when the
two players provide the same output,
this partially verifies that the output is
correct, since it comes from two largely
independent sources; and trying to
agree on the same output with a partner is an enjoyable social experience.
Inversion-problem games.
Resulting from any of three seemingly different games—Peekaboom, 25 Phetch, 23
and Verbosity24—they, in their most
general form (see Figure 3), can be described through the following rules:
Initial setup. Two strangers are randomly chosen by the game itself from
among all potential players;
Rules. In each round, one player is
assigned to be the “describer,” and
the other player is assigned to be the
“guesser.” The describer is given an input. Based on this input, the describer
produces outputs that are sent to the
guesser. The outputs from the describer should help the guesser produce the
original input; and
Winning condition. The guesser produces the input that was originally given to the describer.
Verbosity (see the sidebar) is an
inversion-problem game where the input is a word and the outputs are commonsense facts related to that word.
Following the input word “milk,” the
game might output such facts as “it is
white” and “people usually eat cereal
with it.”
Although the design of Verbosity
involves other game elements not described here, the basic idea is that players need not be asked directly for facts
about “milk.” The game is designed
such that facts are collected as a side
effect of playing. Players told to “please
enter facts about milk” might not be
motivated to do so or enter incorrect
information.
In inversion-problem games, partners are successful only when the describer provides enough outputs for
the guesser to guess the original input.
If the outputs are incorrect or incomplete, the guesser will not be able to
produce the original input. Therefore,
the game structure encourages players to enter correct information. At the
same time, having one player guess the
input while the other describes it is an
enjoyable social interaction, similar to
the popular children’s game “ 20 Questions.”
Additional elements can be added to
inversion-problem games to increase
player enjoyment, including transparency and alternation:
Transparency. In post-game questionnaires, players of inversion-problem games have expressed a strong desire to see their partner’s guesses. We
therefore experimented with adding a
level of transparency between players
so the actions of one would be visible
to the other. In games like Verbosity
and Peekaboom this transparency is
achieved by displaying partner guesses
to the describers and allowing them to
indicate whether each guess is “hot”
or “cold.” This design feature increases the social connection between the
players without compromising output
correctness.
Alternation. Unlike output-agreement games (where both players continually perform the same task), inversion-problem games are asymmetric
in that each player in the pair performs
a different task. In some games of this
type, one of the two roles involves more
interaction or is faster-paced and thus
more enjoyable than the other role. In
such cases, to balance the game and
maintain an equal level of player engagement, player roles can switch after
each round; the guesser becomes the
describer, and the describer becomes
the guesser.
Input-agreement games.
Representing a generalization of games like
Edith Law’s TagATune9 (see Figure 4),
they can be described through the following rules:
Initial setup. Two strangers are randomly chosen by the game itself from
among all potential players;
Rules. In each round, both players
are given inputs that are known by the
game (but not by the players) to be the
same or different. The players are instructed to produce outputs describing
their input, so their partners are able
to assess whether their inputs are the
same or different. Players see only each
other’s outputs; and
Winning condition. Both players correctly determine whether they have
been given the same or different inputs.
In TagATune, the input is a sound
clip, and the output is a series of labels
or tags for the clip. The two players
achieve the winning condition (and obtain points) only if they both correctly
determine whether they have the same
input song. Because players want to
achieve the winning condition, they
each want their partner to be able to
determine if their inputs are the same.
This means it is in their own best interest to enter accurate outputs that appropriately describe their individual
inputs.