Goal

A card shows a shape in a colour, and the tab on the card says which rule to use: COLOUR or SHAPE (and from level 5, COUNT). Each button stands for one colour, one shape and one count — tap the button that matches the card under that rule. The rule keeps changing; answer as many cards as you can in 60 seconds.

Levels

• 8 right answers at a level moves you up; 3 misses in a row move you down.
• Level 1 changes the rule every 4 cards and shows it a moment early. From level 2 it changes at random; from level 3 it appears with the card.
• From level 5 COUNT joins (one shape or two). From level 6 the rule is shown only by the card's border colour — gold for colour, teal for shape, purple for count.
• Levels 7 and 8 give 1.5 and then 1.2 seconds per card.

Scoring

A right answer earns 1 + the level, 1 more if the rule has just changed, plus 1 for every 5 in a row (up to +3). A wrong answer costs 3 + the level and half a second. Running out of time on a card costs only your streak.

Cognitive Flexibility

Dropping one rule and applying another is task switching — what you do every time plans change, you juggle two jobs, or a conversation changes direction.

Your Switch Cost

Everyone is a little slower just after the rule changes. The end card shows how much — and as you train, that gap shrinks.