Episodic memory and personal semantics as triggers of nostalgia: its relationships between abstraction of memory content and temporal distance.

Nostalgia, an autobiographically relevant positive emotion, is a sentimental longing or wistful affection for the past. Autobiographical memory, which is one of the cognitive bases of nostalgia, includes both abstract semantic and detailed episodic memories. Recent studies have defined and classified memories that are located between semantic and episodic memory as personal semantics. Although autobiographical memory and personal semantics range over a continuum, past nostalgia research has not focused on or controlled them. In two experiments, undergraduate students retrieved episodic memory and personal semantics and rated cognitive and affective items. The intensity of nostalgia differed according to the types of memory content and temporal distance of the memory from the present. These results revealed that not only unique events but also repeated events and autobiographical facts induced nostalgia; furthermore, repeated events from both the distant and recent past (primary and high school, respectively) consistently induced relatively greater nostalgia, but in some cases, they were not significantly different from other types of memory (i.e., unique events and autobiographical facts). These findings suggest that both episodic memory and personal semantics are involved in the occurrence of nostalgia.