In the 1970s, however, very few were even aware of its existence, even though it had been around for almost a century.
If you have tried solving this puzzle, you can confirm that your first attempts usually involve sketching lines inside the imaginary square.
The correct solution, however, requires you to draw lines that extend beyond the area defined by the dots.
At the first stages, all the participants in Guilford’s original study censored their own thinking by limiting the possible solutions to those within the imaginary square (even those who eventually solved the puzzle).
In other words, the “trick” was revealed in advance.
Today many people are familiar with this puzzle and its solution.
It was an appealing and apparently convincing message.
Indeed, the concept enjoyed such strong popularity and intuitive appeal that no one bothered to check the facts.
No one, that is, before two different research teams—Clarke Burnham with Kenneth Davis, and Joseph Alba with Robert Weisberg—ran another experiment using the same puzzle but a different research procedure.
Both teams followed the same protocol of dividing participants into two groups.