No Electrophysiological Evidence for Semantic Processing During Inattentional Blindness
A long-standing question concerns whether sensory input can reach semantic stages of processing in the absence of attention and awareness. Here, we examine whether the N400, an event related potential associated with semantic processing, can occur under conditions of inattentional blindness. By employing a novel three-phase inattentional blindness paradigm designed to maximise the opportunity for detecting an N400, we found no evidence for it when participants were inattentionally blind to the eliciting stimuli (related and unrelated word pairs). In contrast, when minimal attention was allocated to the same task-irrelevant word pairs, participants became aware of them, and a small N400 became evident. Finally, when the same stimuli were fully attended and relevant to the task, a robust N400 was observed. In addition to univariate ERP measures, multivariate decoding analyses were unable to classify related versus unrelated word pairs when observers were inattentionally blind to the words, with decoding reaching above-chance levels only when the words were (at least minimally) attended. Our results also replicated several previous studies by finding a "visual awareness negativity" (VAN) that distinguished task-irrelevant stimuli that were perceived compared with those that were not perceived, and a P3b (or "late positivity") that was evident only when the stimuli were perceived and task relevant. Together, our findings suggest that semantic processing might require at least a minimal amount of attention.