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Designer Diary: Stroop, or Coaxing a Game out of an Established Phenomenon

Jonathan Chaffer
United States
Grand Rapids
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Grand Rapids Area Boardgamers
Some things are far more obvious in retrospect. Such is the design of Stroop, a speedy perception card game with simple rules.

Psychological Origins

I can't remember exactly when I first saw a Stroop test. I feel like it was the kind of thing I would have encountered in a GAMES Magazine issue pilfered from my mom's bedside stand. I do recall being delighted by the idea and making flashcards with markers and note cards to test myself and my friends. Throughout the following years I saw it referenced time and again, most notably in the briefly-popular Brain Age game for the Nintendo DS.

The Stroop test is simple. A subject is presented with a series of words, each printed in a different color. The subject is then asked to quickly speak aloud the names of the colors in which the words are printed, and they are timed during this task.

Next, the subject repeats this task, but this time the words are the names of colors, instead of being random words.

This causes the subject to stumble and take longer to complete the task. The experiment demonstrates the Stroop effect, named after psychologist John Ridley Stroop, and shows that the interference between different systems in the brain — in this case, language and color recognition — can slow down both systems.

From Experiment to Game

Flash forward to 2013 when I was in the midst of brainstorming ideas for new tabletop games to develop, and I randomly stumbled across the Wikipedia page for the Stroop effect. This led to the immediate question: Could this be a game?

Now Brain Age had used the Stroop effect in its simplest and most obvious form. It was not really a game, but rather an activity at which you could improve; you were timed on how quickly you responded to the colors and given a score that you tried to improve upon the next time.

The clear way to transform this into a card game was to do exactly the same, but with multiple players. I would print the names of colors onto cards, with ink colors that didn't match. Then players would run through the deck like flashcards, saying the colors out loud and being timed on their effort.

Even before physically prototyping this, it was instantly an unsatisfying implementation. For one thing, a speed contest such as this is usually uninteresting. It is a solo experience that people happen to compare their efforts on, which is something I can enjoy at times but rarely gravitate toward.

But the bigger problem is that the Stroop test can be defeated. Once a subject knows what they are being asked to do, they can use techniques, like squinting, that make the words harder to read, which makes saying the names of the colors much easier. I certainly didn't want players to be able to circumvent the challenge in this way, or worse, to have to make rules against squinting!

Chain, Chain, Chain

The key to cracking this problem was, as is usually the case in design, to come up with the correct incentives for the behaviors I wanted. Need players to read the text and not just squint at blurry colors? Don't make a rule telling them to do read it. Instead, force them to use the text for something.

What purpose could reading the color name serve, then? The clear choice was to link the name of this color up to the color of another word. This forms a nice chain of words, each of which describes the next one.

Exploring Attributes

For the first Stroop prototype, I lifted wholesale the rules of 7 Ate 9, a speed game involving simple arithmetic. Players would race to get rid of their cards by playing onto a central pile, and legal plays consisted of any card that was described by the center one.

In broad strokes, this worked as a game, but it had some issues. The biggest one was the number of potential legal plays on a given card; with eight colors, as in my first prototype, one in eight cards are legal to play. This turned out to be far too small. Iteration revealed that anything smaller than about one in five cards being legal made the game grind to a halt. Shrinking the color space this much, though, made the deck homogeneous and uninteresting.

The solution to this was to introduce additional axes for card descriptors. Aside from color, what else could be used to describe these words? The original Stroop psychology experiments included some other ideas, such as the position of words, but these did not tend to lend themselves to card designs. Instead, I experimented with typography and decided I could easily distinguish the case of a word and could outline it or not.

This was an improvement, but one more axis was needed to flesh out the deck. Some brainstorming surfaced the idea of counting the letters in the words themselves. To make this work, I needed to finesse my color choices, and settled on the following word list:


The final list had the very nice property that each word has 3, 4, 5, or 6 letters, and there are three words of each of those lengths. This meant that, at minimum, one in four cards were legal plays on a given center card.

The Round 2 Head Trip

The 2013 prototype was workable, but the game came into its own in the run-up to Protospiel Michigan in 2014. As my testers began getting very fast with the existing rules, I began looking for ways to provide variants and new challenges. The winner was to reverse the legal play rule: Instead of playing a card that is described by the card in the middle, players now had to read the words on the cards in their hands, and play one that describes the middle card.

The fun of the game is in players getting confused, and how better to confuse people than to switch up the rules midstream? The variant became codified as round two: After the first round is over, scores are recorded and players began anew, with the altered rule for legal plays.

The rules were then simplified to reduce the need for a scoring mechanism. Instead of keeping score, I realized that performance in round one could be used to handicap round two. After round one, players keep their unplayed cards, and the played cards are redistributed evenly, so the better a player performs in round one, the fewer cards they have to get rid of in round two. This neatly determines an overall winner without the need for scorekeeping.

Deck Composition

The possible combinations of attributes could yield a total of 192 cards: 12 words x 4 colors x 2 sizes x 2 patterns. This deck was clearly overkill, so for my working prototype I used half of these combinations, chosen so that exactly half of the cards were big, exactly half solid, exactly one-fourth red, and so on.

I went to some lengths to retain this balance throughout development. When green letters turned out to be difficult to distinguish from blue and yellow in some lighting (and as I endeavored to serve colorblind players as well as possible), I moved to black letters mostly because "black" and "green" both have five letters.

My insistence on a balanced subset of cards turned out to be a bit superstitious; once the card distribution was defined, it could be altered a bit from perfect symmetry without anyone noticing. The final deck has 65 cards, enough for a four-player game, and is slightly uneven without an effect on gameplay.

One improvement in the composition was removing as many "self-describers" as possible. It turned out that players had a reduced challenge in dealing with cards that happened to describe themselves, e.g., a blue card that reads "blue". The final deck has no cards of this type, with the notable exception of the word "four" which inherently describes itself. Now the "run of fours" that can happen in a game just gives a bit of fun texture to the proceedings.

Experiments Along Further Axes

The twelve-word list is enough for most players for quite some time, but I also put some effort into ideas for further expansion to keep the game fresh for as long as possible. Heather Newton gets credit for the seed of the idea for the expansion included in the game box, which features cards with backwards text:

Some other experiments have proved less successful, but fun nonetheless. Never will a typographer squirm so much as if you show them the following card:

Gone Cardboard

And now Stroop is in print! The journey isn't over for me, though, as I'm actively working on variant rules for less stressful games and figuring out what it means to translate this game into a foreign language when word lengths are such an integral aspect of play.

I hope you'll enjoy this tiny brain-twister of a game!

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