From which regions of the brain do conscious representations of visual stimuli emerge? This is an important but controversial issue in neuroscience because some studies have reported a major role of the higher visual regions of the ventral pathway in conscious perception, whereas others have found neural correlates of consciousness as early as in the primary visual areas and in the thalamus. One reason for this controversy has been the difficulty in focusing on neural activity at the moment when conscious percepts are generated in the brain, excluding any bottom–up responses (not directly related to consciousness) that are induced by stimuli. In this study, we address this issue with a new approach that can induce a rapid change in conscious perception with little influence from bottom–up responses. Our results reveal that the first consciousness-related activity emerges from the higher visual region of the ventral pathway. However, this activity is rapidly diffused to the entire brain, including the early visual cortex. These results thus integrate previous “higher” and “lower” views on the emergence of neural correlates of consciousness, providing a new perspective for the temporal dynamics of consciousness.

A flash is perceived to lag spatially behind a moving object even when the two retinal images are physically aligned (flash-lag effect, FLE). Here we show that this robust illusion can be diminished by a knowledge of letters in the observer's brain. When moving and flashed segments in the FLE made the shape of a Kanji letter (ideographic characters used in Japan), the magnitude of the illusory lag perceived by Japanese subjects was significantly reduced compared to when conventional geometric (nonletter) segments were used. This diminishment was not observed when a pseudo-Kanji letter was presented to Japanese subjects or when non-Japanese English-speakers (who do not have a knowledge of Kanji) saw a real Kanji letter, indicating that the reduction in the FLE was induced by a retrieval of the knowledge (shapes of letters) stored in the observer's brain. Furthermore, measurements of neural activities by magnetoencephalography showed that the initial brain response, in which the effect of the knowledge became evident, occurred as early as 160 msec after the appearance of the flashed segment. These results demonstrated a substantial influence of knowledge on the flash-lag illusion and further suggest a rapid response of the knowledge-based perceptual pathway in the human brain.