Atkinson, R. C. (1975). Mnemotechnics in second-language learning. American Psychologist, 30, 821-828.

«THE KEYWORD METHOD
Our initial experiments were not as successful as we had anticipated, but they did help us to develop and refine a mnemonic aid for vocabulary learning that we have dubbed the keyword method. It is this method and related experiments that are discussed in this article. By a keyword we mean an English word that sounds like some part of the foreign word. In general, the keyword has no relationship to the foreign word except for the fact that it is similar in sound. The keyword method divides vocabulary learning into two stages. The first stage requires the subject to associate the spoken foreign word with the keyword, an association that is formed quickly because of acoustic similarity. The second stage requires the subject to form a mental image of the keyword "interacting" with the English translation; this stage is comparable to a paired-associated procedure involving the learning of unrelated English words. To summarize, the keyword method can be described as a chain of two links connecting a foreign word to its English translation. The spoken foreign word is linked to the keyword by a similarity in sound (what I call the accoustic link), and in turn the keyword is linked to the English translation by a mental image (what I call the imagery link).» (p. 821)