Frequency estimation in verbal learning

A multicopy theory of frequency estimation and discrimination is applied to some data found in the literature on verbal learning. The main theoretical assumption adopted is that ‘relevant’ copies generated during study have to be discriminated from ‘irrelevant’ copies as are available in memory from other occasions than the study session proper. At retrieval, copies of either type are added and their sum determines the frequency estimates that are actually reported. A formalization of these ideas is presented and applied to Hinztman's (1969) and Underwood, Zimmerman, and Freund's (1971) data. Two specific models that emphasize either storage or retrieval of copy information are studied. The results show that the models provide a close approximation to the frequency discrimination data. With absolute frequency estimation, both the means and standard deviations of the judgements are predicted reasonably well. However, some reservations were dictated by the fact that, in one instance, the tails of the judgement distributions were not accounted for. The theory offers a theoretical framework for Underwood et al.'s method of cross-relating absolute frequency and forced choice judgements; the usefulness of two approaches to this problem is established. Also, possible extensions of the theory are noted.     

Reconsidering the two-second decay hypothesis in verbal working memory

A common belief in the study of short-term memory is that the verbal trace decays around two seconds after it is encoded. This belief is typically assumed to follow from the finding that in immediate serial recall, the time required to rapidly articulate a span-length list is around two seconds. Empirically, this belief is in opposition to a broad set of findings across a number of domains that establish mean decay times to be longer than two seconds. Theoretically, the available computational and mathematical models of immediate serial recall do not address this issue directly, because they typically rely on other mechanisms in addition to decay to account for forgetting. As such, they may show that decay times can be longer than two seconds, but they fail to show that they cannot be as short as two seconds. We address the issue directly and set a lower bound on mean trace decay times, even under the limiting assumption that all forgetting is due to trace decay. We do this by presenting a simple item-based model of trace decay that allows us to estimate values of mean trace duration. For a set of words whose span-length lists can be rapidly articulated in about two seconds, the model offers a conservative estimate for their mean decay times of around four seconds. Both the experimental and theoretical evidence show that items in verbal working memory decay considerably slower than the two-second decay hypothesis claims.