The nine-dot problem: Beyond perceptual organization
A dozen versions of the nine-dot problem were individually administered. Instructions stating that S could extend his lines beyond the boundary of the square formed by the nine dots were marginally effective in increasing the number of Ss who solved the problem in a 10-min period. Presenting two extra dots outside the square dramatically increased the number of solvers. It was concluded that perceptual organization, seeing the dots as a confining square, is a minor factor in making the problem a difficult one. The source of the difficulty is, instead, the fact that the sequence of lines involved in the solution is nonobvious.