Maier’s “two cord puzzle” and testing heuristics

Norman Maier was an experimental psychologist at the University of Michigan. In 1931, he was interested in exploring how people solve problems and came up with a puzzle which has become known as the “two cord puzzle”.

He attached two cords to the ceiling of his lab and asked people to come up with ways to tie the two ends together. The two cords were placed just far enough apart that, while holding on to one cord, you couldn’t reach the other cord (it wouldn’t be much of a puzzle otherwise!). Some objects were placed around the room – such as extension cords, poles, clamps, and weights – and participants could use any of these items to help them solve his puzzle.

While most people worked out quickly that attaching an extension cord to one of the cords would solve the problem, as would using a pole, these obvious answers didn’t satisfy Maier – he was looking for a different, simple and elegant solution. He would keep asking the participants to come up with new solutions, doing this until they ran out of new ideas.

The elegant solution Maier was looking for was to attach a weight to one of the cords and set it swinging. Then you grab the other rope and can reach the swinging rope when it comes towards you. Very few participants worked out this solution – until they were given a seemingly accidental clue.

Throughout the experiment Maier would wander around the lab until, when people had run out of ideas, he would apparently accidentally brush against one of the ropes and set it swinging. Within a minute of this apparently accidental clue, most people would then come up with the solution.

This experiment shows how easily we can be primed with a solution to a problem – without even realizing it. When the participants in Maier’s experiment were asked afterwards, only one-third of them realized they’d been given a massive clue by him setting one of the ropes swinging. The remainder had stories about how they came to the solution for themselves and, while these stories might have been representative of their conscious experience, they were clearly not the real reason why they solved the problem.

This story got me thinking about testing and, in particular, heuristics. I see heuristics as being these clues to help us as testers find problems in the products we’re testing. While they are not unconscious or accidental when used, experienced practitioners who’ve been using heuristics (and constantly developing their own new ones) over time probably get to the point where their use does become unconscious (“unconscious competence”).

I’m sure you’ve had that feeling where you look at a feature or product and you just know there’s a bug? Maybe that’s a heuristic gently brushing against the product and handing you a clue.

For more about heuristics and their power in testing, try these resources:

• Heuristic Test Strategy Model (James Bach)
• Test Heuristics Cheat Sheet (Elisabeth Hendrickson)
• Michael Bolton’s blog posts on heuristics
• James Bach’s blog posts on heuristics

(I came across Maier’s two cord puzzle while reading Blink by Malcolm Gladwell. This is a great book with lots of testing takeaways, maybe more blog posts to come when I finish reading it.)

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