A connection between quantum theory and human memory came out of cybernetics research in the early 1950s (von Foerster, 1950). It was not until modelling the activation of a word in human memory did the connection begin to appear in mainstream psychological literature. Target word activation was speculated as being similar to quantum entanglement because the target word and its associative network were being activated “in synchrony,” the core intuition behind the “spooky-action-at-a-distance” formula (Nelson et al., 2003). This chapter begins by developing a quantum-like model of the human mental lexicon and compares it against other memory models. Specific attention is paid to how these models describe the activation of a word in memory in the context of the extra- and intra-list cuing tasks. The chapter then covers how quantum theory can be applied to model human semantic space.

The human mental lexicon

A mental lexicon refers to the words that comprise a language, and its structure is defined here by the associative links that bind this vocabulary together. Such links are acquired through experience and the vast and semi-random nature of this experience ensures that words within this vocabulary are highly inter-connected, both directly and indirectly through other words. For example, the word planet becomes associated with earth, space, moon, and so on, and within this set, moon can become linked to earth and star. Words are so associatively interconnected with each other they meet the qualifications of a “small world” network wherein it takes only a few associative steps to move from any one word to any other in the lexicon (Steyvers & Tenenbaum, 2005).