Semantic memory retrieval: Deadlining the typicality effect

Corbett and Wickelgren (1978), employing a speed-accuracy tradeoff method for verifying category membership, found that while the estimated strength of the category-instance association was higher for category examples given more frequently as instances of the category (i.e. higher instance dominance), retrieval dynamics did not vary across levels of instance dominance. The Corbett and Wickelgren data challenged the claims of models of speeded sentence verification that postulated differences in the retrieval processes of high- and low-dominance category-instance associations (e.g. Smith, Shoben, & Rips, 1974). We argued that Corbett and Wickelgren very probably used category instances of debatable membership status in their low-instance dominance category examples, thus making it impossible to decide which responses to these items were correct. This, in turn, rendered their low-instance dominance data uninterpretable. Two partial replications of the Corbett and Wickelgren study were carried out, each with four subjects, and 10 variable lags between the stimulus presentation and the response signal. When care was taken that each category instance clearly belonged to its respective category, an estimate of the rate at which information accumulated towards its asymptote was greater for high-dominance, high-typicality items than for low-dominance, medium-typicality items. However, there were no dominance or typicality differences in the estimates of this asymptotic strength. In contrast, in the study in which low-dominance, low-typicality items were of questionable category membership, the results were similar to those obtained by Corbett and Wickelgren. These data support the idea that there is a continuous accumulation of information in the semantic memory sentence verification task.