Word frequency of irrelevant speech distractors affects serial recall.

In this study, participants memorized frequent or rare target words in silence or while ignoring frequent or rare distractor words. Distractor words impaired recall performance, but low-frequency distractor words caused more impairment than did high-frequency distractor words. We demonstrate how to solve the identifiability problem for Schweickert's (1993) multinomial processing tree model of immediate recall, and then use this model to show that irrelevant speech affected both the probability with which intact target word representations were available for serial recall and the probability of successful reconstruction of item identities based on degraded short-term memory traces. However, the type of irrelevant speech--low-versus high-frequency words--selectively affected the probability of intact target word representations. These results are consistent with an explanation of the irrelevant speech effect within the framework proposed by Cowan (1995), and they pose problems for other explanations of the irrelevant speech effect. The analyses also confirm the validity of Schweickert's process model.