There are three components of memory games: position of card, card, and study period. The study period refers to the presentation of information and the time allocated to players. For example, we can present all the information to be memorized at once or partially.
Take the game Memory where there are duplicates of cards in a grid; you flip up cards two at a time, memorize them, and replace them. Naturally, players learn the positions of cards overtime and are able to select them and remove them from the game. Compare this to a game where all the cards are revealed at once: a player has a chance to memorize all the cards, then the cards are flipped over and then he identifies pairs.
When playing Memory, often one remembers a card that has been revealed but not the position. Or oppositely one can remember the positions and sequences of cards that were flipped over, seeing the grid as a grid of where cards have been flipped over. Suppose, you can only remember which cards have been revealed but not their place, then a strategy is: when the sequence of cards in memory has a duplicate, to choose a card that has been flipped over, hoping that you choose the duplicate. In competitive Memory, a strategy if you do not remember the cards is to continue flipping over new cards. Now if a future player tries to reveal the duplicate and fails, then he has eliminated a possibility and perhaps has helped jog your memory as to where the duplicate truly is. The gestalt of card positions is a highly memorable feature.
Another game that is more about card positions than the cards themselves is often played on a computer with a simple grid where grid squares can be turned light or dark. In this case, the gestalt of card positions is the basis for the game. In a short frame of time, a few seconds, a player will see all the positions and then on a separate grid will try to duplicate all the positions. How someone is able to memorize all the positions so quickly is a bit of a mystery. The brighter lights sear a pattern into the visual system. If there are not too many squares, then a person can code the pattern like, “4 connected in an L starting on this square, etc.” quickly in their head.
Another separate part of the memory game is the cards themselves. The cards for example might have a sequence of numbers on them or other relations between them like color or pattern; picture, imagery. We could play a different version of Memory where we are asked by a third party to recover certain cards that may or may not have been revealed instead of just duplicates as a hypothetical example. Another possibility might be to present the information to study in different ways than all or one at a time. All cards of a type might be revealed. This lacks a kind of elegance compared with Memory as a third party is needed to give these presentations.