Effects of perceptual and working memory load on brain responses to task-irrelevant stimuli: Review and implications for future research

Load Theory assumes that the extent of processing of task-irrelevant information depends on the level (high vs. low load) and type (perceptual vs. working memory) of task load. In this review, we address the neuroscientific perspective on Load Theory by a systematic evaluation of neuroimaging and electrophysiological studies, which manipulated perceptual or working memory load and reported brain responses to task-irrelevant unimodal and crossmodal stimuli. Studies show: (1) Load effects can be observed across the whole processing stream from subcortical areas to higher cortical areas, (2) both higher perceptual and working memory load lead to decreased distractor processing, (3) event-related potential studies suggest that load effects occur more reliably the later the ERP component and (4) load effects occur both within and across modalities. Thus, findings are at least partially consistent with assumptions of Load Theory. Based on the reviewed studies and theoretical and methodological considerations, we provide several suggestions, which might help to improve future research in the field.