Neural Hierarchy of Color Categorization: From Prototype Encoding to Boundary Encoding.

Area of Science:

• Cognitive Neuroscience
• Neuroimaging
• Visual Perception

Background:

• The neural basis of color categorization remains debated, with fMRI studies implicating various brain regions with mixed results.
• Previous research often focused on differences between categories, neglecting within-category variations like prototypes and boundaries.

Purpose of the Study:

• To investigate how the brain encodes fine-grained perceptual representations of color within and across categories.
• To explore the role of within-category variability (e.g., prototypes, boundaries) in color categorization.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to compare brain activity during an active color categorization task.
• Brain responses to color stimuli at varying distances from category boundaries were modeled.
• Representational Similarity Analysis (RSA) was employed to analyze neural patterns.

Main Results:

• Frontal areas (inferior/middle frontal gyri, medial superior frontal, insular cortices) showed heightened activity for colors near category boundaries.
• The visual cortex (V1, V4) encoded both within-category variability and cross-category differences, with specific responses to category centers and boundaries.
• Bilateral insulae and V4a distinguished between within-category and cross-category colors, as indicated by representational dissimilarities.

Conclusions:

• A hierarchically organized network supports active color categorization.
• Frontal regions likely handle domain-general decision-making processes.
• The visual cortex encodes color category structure and differences, potentially via top-down modulation.