Fixed and random address models for storing order in short-term memory

Two models have been proposed for storing order in short-term memory. Conrad's (1965) fixed address model assumes that items are kept in a set of fixed addresses, while Crossman's (1961) random address model assumes that items are tagged for order, and assigned to a set of random addresses. Experiment I tested the models in a task where six items were presented visually and either watched silently or shadowed. Memory for the position of one of them was tested with a probe. Neither model fitted the data, and it was suggested that order might pass through two stages in memory, the first being a buffer store with properties like the fixed address model, and the second being a longer-term store which behaves like a set of random addresses. Simulations of a combined fixed and random address model produced results like those of Experiment I, and in Experiment II response latencies were used to separate the buffer and longer term store stages. Responses with short latencies produced results like those from a buffer with fixed addresses, while responses with long latencies conformed more to the predictions of a random address model.