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).
Even though they weren’t instructed to restrain themselves from considering such a solution, they were unable to “see” the white space beyond the square’s boundaries.
Today many people are familiar with this puzzle and its solution.
The first group was given the same instructions as the participants in Guilford’s experiment.
Guilford was one of the first academic researchers who dared to conduct a study of creativity.
He challenged research subjects to connect all nine dots using just four straight lines without lifting their pencils from the page.
The second group was told that the solution required the lines to be drawn outside the imaginary box bordering the dot array.
In other words, the “trick” was revealed in advance.