Interpretations: For “Marco’s Number Series” every integer has (at least) two
possible neighbors – with the exception of “8” or “9” who have to start or end the row.
Most of the novices worked this problem by trying, that is starting the row with any
number and continued it by adding numbers to the right until they got stuck and started
with a different number. Three pupils solved this task by looking for patterns: they
listed the possible neighbors for each integer and realized this way that they had to start
with “8” or “9”. Three other pupils solved it by showing mental flexibility: they added
numbers to the right as well as to the left when working on either side came to a stop.8
The experts did not have to use the heuristic looking for patterns; they all proved to be
mentally flexible by adding numbers on both sides of their rows naturally.
The same is true for the “Beverage Coasters” task. Only a few of the novices were able
to rotate the squares mentally around each other. The others had to sketch figures of the
squares in different positions and one even used a cut-out paper square to imagine their
possible positions. Most of the experts, on the other hand, claimed to “see easily” that
the area covered by both squares is one fourth of a square in every possible position.9
For the “Squares on a Chessboard” task, only 5 of 19 novices realized that there are
squares of every size from 1x1 to 8x8. Those who did were not able to see a pattern in
the number of squares or to count them correctly. All the experts realized almost
immediately that there are squares of all sizes and all but one pair (who did a “wild
goose chase” on this task) found a pattern10 to count those squares quickly.
These findings support the claim of Bruder and Collet (2011) that a lack of mental
flexibility can be compensated by the use of heuristics. All the experts showed mental
flexibility in each of the tasks without the need to use as much heuristics as the novices.