The pillar experiment from the paper isn't fully explained in the article. The instructions stated "You may alter the structure however you want".
The experiment was run with two groups, both of which were given equal costs on addition – "Each piece that you add costs ten cents". There was also a group given a 'subtraction-cue' where the instructions mentioned that "removing pieces is free and costs nothing". Increase from 41% to 61% use of subtractive method.
There was a cost to addition, so the optimal solution for both groups was removal of the pillar.
The experiment was run with two groups, both of which were given equal costs on addition – "Each piece that you add costs ten cents". There was also a group given a 'subtraction-cue' where the instructions mentioned that "removing pieces is free and costs nothing". Increase from 41% to 61% use of subtractive method.
There was a cost to addition, so the optimal solution for both groups was removal of the pillar.