When the rule changes under you
Sort by shape, then suddenly by colour, and nobody tells you: noticing the switch from your own mistakes is the skill.
Your brain builds a habit for the current rule within a few answers.
When the rule flips, the old habit keeps firing: those wrong answers are the signal.
Reading that signal and switching fast is cognitive flexibility.
Then and now
Card-sorting is still the clinical standard for flexibility; the modern account explains WHAT shifts: attention, rules, and perspectives.
Berg, E. A. (1948)
Where it began“A simple objective technique for measuring flexibility in thinking”
Journal of General Psychology, 39, 15-22
Introduced the card-sorting method behind the Wisconsin Card Sorting Test: rules change without warning and flexibility is measured by adaptation.
Diamond, A. (2013)
State of the art“Executive Functions”
Annual Review of Psychology, 64, 135-168
Cognitive flexibility (set shifting) is one of the three core executive functions, built on inhibition and working memory.
What we do and do not claim
Our silent rule swaps are the same mechanic made playable. It trains switching in the game, plainly measured.