Long-term or episodic memory can be understood along several dimensions, including verbal vs abstract, spatial vs nonspatial, and item vs relational memory. The latter has represented a field of growing interest over the past 15 years, particularly in cognitive neuroscience and neuroimaging. In basic terms, item memory is a metric related to a single piece of information, whereas relational memory involves forming a relationship between 2 or more pieces of information. Relational memory can occur within many contexts such as linking multiple objects together (eg, “I saw x with y.”) or within a spatial or temporal context (eg, “I saw x at the park in the afternoon.”). However, relational memory cannot be considered successful in the absence of item memory (eg, “I saw someone at the park.”). Relational memory requires more elaborate processing to create associations that can later be recalled together. By consequence, memory performance for individual items can be improved with deep semantic encoding (eg, combining items into groups) as opposed to shallow encoding (eg, remembering items individually). Not surprisingly, forming relationships between items is easiest when items share semantic features such as category (eg, hammer and screwdriver are tools).
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