The brain detects stimulus features, but not stimulus conflict in task-irrelevant sensory input

Cognitive control over conflicting sensory input is central to adaptive human behavior. It might therefore not come as a surprise that past research has shown conflict detection in the absence of conscious awareness. This would suggest that the brain may detect conflict fully automatically, and that it can even occur without paying attention. Contrary to this intuition, we show that task-relevance is crucial for conflict detection. Univariate and multivariate analyses on electroencephalographic data from human participants revealed that when auditory stimuli are fully task-irrelevant, the brain disregards conflicting input entirely, whereas the same input elicits strong neural conflict signals when task-relevant. In sharp contrast, stimulus features were still processed, irrespective of task-relevance. These results show that stimulus properties are only integrated to allow conflict to be detected by prefrontal regions when sensory information is task-relevant and therefore suggests an attentional bottleneck at high levels of information analysis.