Subjective Visibility Enhances Early Posterior EEG Decoding of Stimulus Location across Report and No-report Tasks

Abstract

A central question in consciousness research is whether perceptual awareness is primarily reflected in early posterior sensory activity or in later frontal processes associated with access and report. Empirical tests of these alternatives are challenging because most paradigms rely on explicit perceptual reports, introducing motor and decisional confounds. Here, we used an electroencephalography design combining two independent tasks to decode stimulus location across report and no-report conditions and to examine how these task-general stimulus-location signals vary with subjective visibility. Participants viewed lateralized gratings in a backward-masking task and rated their subjective visibility, whereas in a separate no-report task, they viewed unmasked gratings without reporting. Classifiers were trained on stimulus location in the no-report task and tested on masked trials sorted by subjective visibility in the masking task. This cross-decoding approach identifies stimulus-location signals that generalize across tasks and vary with subjective visibility, making them less likely to reflect reporting or decision-related processes. Decoding revealed stronger stimulus-location signals for subjectively visible than invisible stimuli in an early time window from 130 to 170 msec, most prominently over posterior occipital, temporal, and parietal electrode groups. These results indicate that subjective visibility enhances early posterior EEG decoding of stimulus location across report contexts.