Temporal Dynamics of Visual Awareness as a Function of the Level of Processing of the Stimulus and Report Requirements: An ERP Study.

Abstract

Recent evidence suggests that the stimulus level of processing (LoP) modulates the two event-related potential (ERP) correlates of visual awareness-the visual awareness negativity (VAN) and late positivity (LP)-yet it remains unclear whether LoP also affects their temporal dynamics. In addition, recent studies using no-report paradigms have raised doubts about whether the LP constitutes a genuine correlate of awareness. In this study, we examined the ERP correlates of visual awareness and its temporal dynamics as a function of stimulus level of processing (LoP) and report condition (report vs. no-report). In the report condition, participants performed either a low-level (color: blue vs. red) or high-level (category: animal vs. object) discrimination task and indicated whether they had seen the target. In the no-report condition, they counted occurrences of a task-irrelevant but LoP-congruent stimulus. We computed the VAN and LP by pooling aware and unaware trials within each condition. The VAN component was absent in both tasks and report condition, likely influenced by early sensory activity and variations in stimulus-mask SOA. The LP was clearly visible across conditions, yet its amplitude was not modulated by the LoP. Critically, significant LP components were observed in both report and no-report conditions; although attenuated and slightly delayed in no-report trials, the LP remained present. This pattern replicates previous findings showing that the LP/P3 is sensitive to post-perceptual task demands yet also shows that it may persist even when response-related processes are removed. These findings suggest that late post-VAN activity may not correspond to a single unified ERP component but rather reflect a combination of post-perceptual processes and aspects of conscious stimulus evaluation.