Individuals with high working memory capacity (WMC) are less distracted by task-irrelevant speech than others. The mechanism behind this relationship, however, is not well understood, and it has only been found in a few paradigms. We used a Number updating task to measure WMC and two suppression mechanisms (immediate and delayed), and tested how they were associated with individual differences in susceptibility to the effects of speech on reading comprehension. The results revealed a negative relationship between WMC and susceptibility to speech distraction. Of the two suppression mechanisms, only immediate suppression was associated with speech distraction, suggesting that susceptibility to distraction is determined by the ability to immediately suppress the irrelevant speech. Furthermore, the relationship between WMC and speech distraction was mediated by the immediate suppression mechanism. The implications of these results and possible explanations of similar results found in other paradigms are discussed.

In this article we outline a "sub-process view" of working memory capacity (WMC). This view suggests that any relationship between WMC and another construct (e.g., reading comprehension) is actually a relationship with a specific part of the WMC construct. The parts, called sub-processes, are functionally distinct and can be measured by intrusion errors in WMC tasks. Since the sub-processes are functionally distinct, some sub-process may be related to a certain phenomenon, whereas another sub-process is related to other phenomena. In two experiments we show that a sub-process (measured by immediate/current-list intrusions) is related to the effects of speech on prose memory (semantic auditory distraction), whereas another sub-process (measured by delayed/prior-list intrusions), known for its contribution to reading comprehension, is not. In Experiment 2 we developed a new WMC task called "size-comparison span" and found that the relationship between WMC and semantic auditory distraction is actually a relationship with a sub-process measured by current-list intrusions in our new task.

Previous research indicates that aircraft noise and meaningful background speech are particularly detrimental to school adolescents’ ability to remember what they read, but until now the effects from aircraft noise and speech have never been compared directly in an experiment. Furthermore, individual differences in susceptibility to these effects are not well understood. The present investigation addressed these two issues. Adolescents attending upper secondary school were recruited as participants and the data collection was made in their ordinary classrooms. The results from two experiments revealed that speech is more detrimental to prose memory than is aircraft noise, and individual differences in working memory capacity contributes more to individual differences in susceptibility to the effects of aircraft noise on prose memory than to the effects of speech. Some applied implications of those findings to noise abatement interventions are suggested.

Serial short-term memory is impaired by background sound, at least when a sound element suddenly deviates from an otherwise repetitive sequence (the deviation effect) and when each sound element in the sequence differs from the preceding one (the changing-state effect). Two competing theories have been proposed to explain these effects: One suggests that both effects are caused by the same mechanism (i.e., attentional resources being depleted by the sound), and the other suggests that the deviation effect is caused by attentional capture and that the changingstate effect is caused by interference between order processes. The present investigation found that working memory capacity predicts susceptibility to the deviation effect, but not to the changing-state effect, both when speech items (Experiment 1) and when tones (Experiment 2) produce the disruption. These results suggest that the two effects are caused by different mechanisms and support the duplex-mechanism account of auditory distraction.