Rapid Color Categorization in the Brain Revealed by Frequency-tagging-based EEG

Abstract

The origin of color categories has been debated extensively. Historically, linguistic relativists claim that color categories are shaped by the language we speak and that color terms subsequently affect our perception of color, while universalists postulate that color categories are independent of language and formed based on perceptual mechanisms. A recent hypothesis suggests that the original fine-grained color space in the visual cortex may be transformed into categorical encoding due to top-down modulation. To test the nature of color categorization, our study adopted a sensitive frequency-tagging-based EEG paradigm where the color stimuli were presented sequentially at a fast speed of 10 Hz (SOA: 100 ms) to probe fast, implicit processing of color categories. This SOA was supposed to disrupt top-down feedbacks in visual processing. We showed that EEG responses to cross-category oddball colors at the frequency where the oddball stimuli were presented was significantly larger than the responses to within-category oddball colors. This finding suggested that the brain encodes color categories automatically when top-down feedbacks from frontoparietal areas are blocked. Our study supports the view that the categorical processing of color emerges at the early perceptual stage.