A surprising validation of expectation experienced during a recognition test induces the perception of discrepancy and a feeling of familiarity. The authors investigated whether that perception also affects memory performance when it is experienced in the original encounter with a stimulus. Target words were presented in a study phase, half in a context thought to induce the perception of discrepancy. In a subsequent recognition test, that earlier experience increased the accuracy of subjects' discrimination. However, when the subsequent task required a once-versus-twice judgment, that experience caused an illusion of reoccurrence for words presented once. The authors concluded that a perception of discrepancy in an initial encounter may be a valuable aid to later recognition but can also cause systematic memory errors under some circumstances.