Cognitive Flexibility Index

Cognitive Flexibility Index is a real, live implementation of the Wisconsin Card Sorting Test (Berg, 1948; Grant & Berg, 1948) — the defining neuropsychological measure of set-shifting. You sort cards under four key cards by a rule (color, shape, or number) that is never stated — you infer it from right/wrong feedback, and once you've found it, it silently shifts to a new rule after 6 consecutive correct sorts. Getting caught applying the old rule after a shift (a "perseverative error") is the classic clinical signal WCST is built to detect.