After reading about memory tests, I thought up a variant for my Concentration game. The user first sees the card layout. When ready, the user clicks on the 'Blink' menu item or button. The program then displays the card pairs for X seconds and then only shows the card backs. In order to rely on memory only, the program only indicates match success or failure by changing the colors of the card backs.
A couple of options to make the game even more sadistic. One, if the user can match cards in under an arbitrary number of attempts, the program automatically shortens the time that the cards are displayed when the user clicks 'Blink'.
The second, and worse, is to have the computer revert the display of the successful matches to 'un-played' after a short time. Not only would the user have to memorize the card positions, but the successful matches as well. Of course matching a pair of cards the second or more time would not go to the score.
This observation / memory training game is not a new idea. I have come accross it elsewhere, but the only place that I definitly remember it is in Heinlein's "Citizen of the Galaxy". Here a bunch of odds-and-ends are thrown on the ground / a tray / the table and then covered after a short time. Not only must the player remember what objects were thrown, the position and orientation (if possible) has to be remembered as well.