The memory viewer is a device that allows its user to see certain moments of his adventure. It has the same function as Julia's TV or the ball in Well of Sendell in LBA. It can be found in Baldino's house, or bought in the twinsonian souvenir shop for 30 kashes.
When Twinsen uses the memory viewer, all the cinematics from the game that he has experienced are played in a non-chronological sequence.
"The memory viewer allows you to review the sequences which have punctuated your adventure."