In most cases, the term "reinforcement" refers to an enhancement of behavior, but this term is also sometimes used to denote an enhancement of memory; for example, "post-training reinforcement" refers to the provision of a stimulus (such as food) after a learning session in an attempt to increase the retained breadth, detail, and duration of the individual memories or overall memory just formed. The memory-enhancing stimulus can also be one whose effects are directly rather than only indirectly emotional, as with the phenomenon of "flashbulb memory," in which an emotionally highly intense stimulus can incentivize memory of a set of a situation's circumstances well beyond the subset of those circumstances that caused the emotionally significant stimulus, as when people of appropriate age are able to remember where they were and what they were doing when they learned of the assassination of John F. Kennedy or of the September 11, 2001, terrorist attacks.