It is a test that can be used to monitor frontal lobe activity and detect frontal lobe dysfunction. It requires you to change your "cognitive strategies" so by doing this trained psychologists are able to measure executive functions that primarily take place in the frontal lobes.

Example: You are normally asked to sort the cards either by color or shape (in in some instances the cards also have a number you can sort by) and throughout the test the test administrators will change what category (color vs. shape) you are sorting by. It sounds easy but gets tricky because of conflicting executive functions and choosing the correct one.