Illuminating the Unconscious: Physical and Perceived Brightness in Cognitive Processing

Abstract This study investigated how physical luminance and perceived brightness affect breakthrough time (BT) under continuous flash suppression (CFS). Experiment 1 examined whether the glare illusion—which increases subjective brightness without altering actual luminance—would shorten BT compared to physically identical controls. The results revealed no difference, suggesting that subjective brightness alone does not expedite emergence into awareness. Experiment 2 assessed whether the partial suppression of the illusion’s inducers influenced detection speed and revealed that subjective brightness stimuli gained a BT advantage. Experiment 3 tested participants’ ability to discriminate real versus illusory brightness while stimuli remained suppressed; performance above chance for both conditions indicated that physical and perceived brightness cues were processed unconsciously. Together, these findings suggest that contextual brightness illusions are not simply lost below awareness—they can be discriminated in unconscious vision. Statement of Relevance Understanding how the visual system processes brightness illusions—even prior to awareness—is crucial for uncovering the brain’s deeper mechanisms of perception. This research clarifies the limits of unconscious visual processing by showing that illusions can be registered without consciousness but do not necessarily expedite emergence into awareness. These insights advance theoretical models of hierarchical vision and demonstrate that while early cortical areas prioritize actual luminance in determining whether a stimulus reaches awareness, higher areas can still encode illusory brightness beneath the threshold of consciousness. Thus, the study’s findings have broad implications for both basic neuroscience—refining how we think about the boundary between unconscious and conscious perception—and for applied fields seeking to harness or mitigate perceptual illusions. Preregistration All experiments were not preregistered. Conflicts of interest The authors declare that they have no competing interests. Data availability The code and data underlying the results presented in the study are available from the Open Science Framework repository (https://osf.io/u5der/). Ethics The Committee for Human Research of the Toyohashi University of Technology approved the experiments (2023-20). Written informed consent was obtained from all participants after the procedural details were explained to them. Funding This work was supported by JSPS KAKENHI (Grant Numbers JP22K17987 to H.T., JP24H01551 to T.M., JP23KK0183 to T.M., JP20H05956 to S.N.), JSPS Grant-in-Aid for JSPS Fellows (Grant Number JP24KJ1313), and Young Principal Investigator fund JPMJFS2121. Artificial intelligence During the preparation of this work, the authors used ChatGPT o1 and Grammarly to improve the language, and the manuscript was proofread by native English speakers through an English editing service. After using the tool and service, the authors reviewed and edited the content as needed, and they take full responsibility for the content of the publication. Competing Interest Statement The authors have declared no competing interest. Footnotes Author note The authors made the following contributions. Hirotaka Senda: Conceptualization, Methodology, Software, Validation, Formal analysis, Visualization, Data Curation, Writing - Original Draft, Writing - Review & Editing; Michael Makoto Martinsen: Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data Curation, Project administration, Writing - Original Draft, Writing - Review & Editing; Hideki Tamura: Resources, Writing - Review & Editing, Supervision, Project administration, Funding acquisition; Shigeki Nakauchi: Resources, Writing - Review & Editing, Supervision, Funding acquisition; Tetsuto Minami: Conceptualization, Investigation, Resources, Writing - Review & Editing, Supervision, Funding acquisition.