Random-walk modeling of free-recall anomalies - Part 1: Contiguity and inter-response intervals

A comparison of three different experimental datasets leads to the identification of an apparently robust feature of free-recall data: a minimum in the rate of contiguous recall near the beginning of the recall process. By simulating verbal retrieval as a homogenous Markov chain with the experimentally observed transition matrix, I show that this behavior cannot be explained in terms of the nonequilibrium initial conditions. I deduce that the process, if markovian, is inhomogenous and I identify a psychological mechanism that would effectively lead to a time-dependent transition matrix. The theory is based on the simultaneous coexistence of competing random walks, all of them homogenous but liable to losing permanently the right to effect retrieval. To test this hypothesis, I construct a many-particle model governed by two free parameters and simulate it with initial conditions taken from the data. Besides reproducing the contiguous-recall curve, the theory leads to a counterintuitive prediction on the behavior of the inter-response intervals as a function of the serialposition lag. Data are found to confirm this prediction. I proceed then to investigate possible consequences of the model, drawing in part on a comparison with classical results from experiments on category recall.