The task is only to count the 3D shapes of the specified shape and color, but as the N of the N ‘Back increases, it becomes more difficult. *N’Back : The current answer matches the one from N steps earlier in the sequence. *1’Back 1 task1: count & memorize 2 task2: count & memorize 3 answer for task1 4 task3: count & memorize 5 answer for task2 6 task4: count & memorize : *2’Back 1 task1: count & memorize 2 task2: count & memorize 3 task3: count & memorize 4 answer for task1 5 task4: count & memorize 6 answer for task2 7 task5: count & memorize :