Central load reduces peripheral processing: Evidence from incidental memory of background speech

Is there a trade‐off between central (working memory) load and peripheral (perceptual) processing? To address this question, participants were requested to undertake an n‐back task in one of two levels of central/cognitive load (i.e., 1‐back or 2‐back) in the presence of a to‐be‐ignored story presented via headphones. Participants were told to ignore the background story, but they were given a surprise memory test of what had been said in the background story, immediately after the n‐back task was completed. Memory was poorer in the high central load (2‐back) condition in comparison with the low central load (1‐back) condition. Hence, when people compensate for higher central load, by increasing attentional engagement, peripheral processing is constrained. Moreover, participants with high working memory capacity (WMC) – with a superior ability for attentional engagement – remembered less of the background story, but only in the low central load condition. Taken together, peripheral processing – as indexed by incidental memory of background speech – is constrained when task engagement is high.