  A stochastic model of short-term verbal memory is proposed, in which the
psychological state of the subject is encoded as the instantaneous position of
a particle diffusing over a semantic graph with a probabilistic structure. The
model is particularly suitable for studying the dependence of free-recall
observables on semantic properties of the words to be recalled. Besides
predicting some well-known experimental features (contiguity effect, forward
asymmetry, word-length effect), a novel prediction is obtained on the
relationship between the contiguity effect and the syllabic length of words;
shorter words, by way of their wider semantic range, are predicted to be
characterized by stronger forward contiguity. A fresh analysis of archival data
allows to confirm this prediction.
