Involuntary attentional orienting in the absence of awareness speeds up early sensory processing

A long-standing controversy in the field of human neuroscience has revolved around the question whether attended stimuli are processed more rapidly compared to unattended stimuli. We conducted two event-related potential (ERP) experiments employing a temporal order judgment procedure in order to assess whether involuntary attention accelerates sensory processing, as indicated by latency modulations of early visual ERP components. A non-reportable exogenous cue could precede the first target with equal probability at the same (compatible) or opposite (incompatible) location. The use of non-reportable cues promoted automatic, bottom-up attentional capture, and ensured the elimination of any confounds related to the use of stimulus features that are common to both cue and target. Behavioral results confirmed involuntary exogenous orienting towards the unaware cue. ERP results showed that the N1pc, an electrophysiological measure of attentional orienting, was smaller and peaked earlier in compatible as opposed to incompatible trials, indicating cue-dependent changes in magnitude and speed of first target processing in extrastriate visual areas. Complementary Bayesian analysis confirmed the presence of this effect regardless of whether participants were actively looking for the cue (Experiment 1) or were not informed of it (Experiment 2), indicating purely automatic, stimulus-driven orienting mechanisms.