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- 🧠 Shared brain regions like V1, V2, and hV4 encode color consistently across individuals.
- 🧬 Retinotopic mapping enables alignment of visual brain activity without using color stimuli.
- 🧪 Machine learning models predicted viewed colors using brain data from different people.
- ⚠️ Neuroscience can’t yet access the subjective experience or qualia of color perception.
- 🧠 Color bias in perception depends on both brain region and spatial location in the visual field.
Color Perception: Do All Brains See Color the Same?
Is your red the same as mine? People have wondered about this for centuries, in philosophy, art, and psychology. Red is on the light spectrum, but your brain shapes how you experience it. It turns out your brain might not be that special after all. Thanks to new science, researchers are finding out how our brains process color in similar ways. This shows how our brains react in very similar ways when we see the same colors. Scientists use brain activity patterns and careful models to figure out what color a person is seeing. This could be a big step to understand how all brains process color.
The Science of Seeing Color
Color may seem like something real in the world, but the brain makes it. It starts with how light, wavelength, and our visual system work together. Light waves bounce off objects and hit the retina at the back of the eye. Cone cells, which are light-sensing cells that respond to different light waves, detect them.
There are three types of cones in the human eye:
- S-cones, which are sensitive to short wavelengths (blue light)
- M-cones, for medium wavelengths (green light)
- L-cones, for long wavelengths (red light)
This three-color signal system sends electrical impulses through the optic nerve to the brain. These signals first go to the primary visual cortex (V1). Then, they move through different visual areas, like V2, and into hV4, a part of the brain very important for processing color.
But color is not seen alone. The brain processes visual information, and it also considers edges, context, and lighting conditions. This lets us see colors the same way even when the light changes. This is called color constancy.
So, the brain computes color; it’s not just raw light data. The brain interprets what it senses using organized activity patterns. This creates our strong, steady experience of color.
The Challenge of Measuring Subjective Experiences
What a person feels when they see a color is still something we cannot measure from the outside. This issue is about qualia, an old idea. Qualia are the personal, felt parts of conscious experience. We can record nerve signals or blood oxygen levels with fMRI. But this still does not show us “what it’s like” to see green grass or a red dress.
Philosophers and cognitive scientists have long argued if qualia are the same for everyone or only personal. In modern science about the brain, this difference has real effects:
- Decoding perception means matching things we see (like colors) to clear patterns of brain activity.
- Decoding consciousness, on the other hand, tries to understand the inner, personal feeling linked to what we see.
Even with more data and better technology, figuring out qualia is still part of what philosopher David Chalmers calls the “hard problem” of consciousness. We can show how visual systems work, but we cannot yet understand how they feel to someone.
New Research in Color Decoding Using Brain Activity
In an important 2025 study published in The Journal of Neuroscience, neuroscientists Michael Bannert and Andreas Bartels looked at whether we could tell what color a person saw using someone else’s brain data. This new idea pushed what machine learning and brain-to-brain comparison could do.
The researchers used functional magnetic resonance imaging (fMRI) to see brain activity patterns. Participants viewed both grayscale and color images. They used smart ways to line up data, especially Shared Response Modeling (SRM). This let the team make a common brain space. In this space, they could check how visual brain responses were alike across different people.
The new idea was how they did the study: lining up brains using black and white images. Participants first viewed black-and-white checkerboards. This let researchers make a map of how each person’s brain responded to space. Once these “maps” were lined up by spatial location, they then showed color images to test predictions for other people.
The main question was: Could they tell what color someone saw just by using models trained on other people’s brains?
What Is Retinotopic Mapping (and Why Color Doesn’t Matter Here)
To understand how different brains process visual space, researchers use a method called retinotopic mapping. They slowly moved clear checkerboard patterns (like spirals or rings that got bigger) across what a person saw. At the same time, they used fMRI to track brain activity.
The visual cortex, starting with V1, is known to have an organized layout. This means certain brain areas respond to certain spots in what you see. For instance:
- Images in the upper-left part of your visual field make a certain patch in your visual cortex active.
- What you see right in the middle (foveal vision) takes up more brain space. This is because there are many cones there.
This mapping creates a visual “pattern” for each person’s brain. The patterns of activity are based on spatial location, not color. This technique helps line up data from different participants in a way that does not depend on the image itself.
When they matched these retinotopic layouts, the study made sure that later color checks had a shared base structure. It’s like matching GPS systems before comparing travel routes.
Predicting Color by Aligning Brains in “Neural Space”
After setting up each participant’s brain through retinotopic mapping, the study used a machine learning method called Shared Response Modeling (SRM). This moved the data into a shared space where information could be shown. This method pulls out the most useful patterns that many people’s brains share. It does this without focusing too much on small personal differences.
SRM shows main responses that work the same way but can be in different brain spots. Once the shared space is set up with black and white images, researchers can then show colored images. They record activity for some people. This trains a classifier to spot certain colors.
Most importantly, this classifier is then tested on data from new people. These people’s brains were only lined up by space, not by color. If the classifier correctly tells what color the test person saw, it shows that certain ways of processing color are common among people.
What happened? The system could correctly tell if a person saw red, green, or yellow. This was true even when their color responses were not in the training data.
Cross-Brain Color Decoding: The Surprising Results
The model was very accurate, especially in early and middle visual areas:
- V1: the main visual cortex, sensitive to basic visual features.
- V2: uses V1 input to find out about directions, edges, and some color details.
- hV4: very involved in processing color in different situations.
- LO1: connected to recognizing objects and more complex visual processing.
These results suggest that organized brain activity patterns record color perception the same way across brains, at least in these areas. This shows a shared “brain language” for color. Brain structure and circuits seem to decide this more than personal ways of seeing.
Interestingly, other brain areas, like the prefrontal cortex, might understand or put colors into context differently. But the start and middle visual areas seem to process color in a very similar way across all people.
This sameness is important for making brain models that work for many people. This is useful in vision research, but also for brain-computer interfaces and checking how the brain works.
Color Bias in Different Visual Field Regions
The study did not just find which colors everyone could recognize. It also found a bias in how those colors were seen based on where they showed up in the visual field.
- Yellow images made stronger responses when placed in the center of where someone looked (Foveally).
- Red and green images showed more activity in the outer parts of what someone saw.
Why does this matter?
This finding shows that the brain shows color in terms of both color type and location. The physical structure of the retina backs this up:
- There are most cones in the fovea, especially for L- and M-cones (which help us see red and green).
- And some color paths might be more sensitive to images depending on how far they are from the center of vision.
In practice, this means our visual system might automatically give certain colors more importance in different visual areas. This bias could come from evolutionary benefits, like spotting ripe fruit (red/yellow) in busy places.
What Neuroscience Can and Can’t Say About Color Qualia
Even with new technical findings and how well they can predict things, they do not fully solve the puzzle of personal experience—what philosophers call “qualia.”
The question remains: Even if our brains show the same activity patterns when seeing red, does your red feel the same as mine?
Bannert and Bartels warn against saying that brain likeness means conscious experience is alike. In neuroscience, this shows the difference between:
- Access consciousness: information we can process, act on, and talk about.
- Phenomenal consciousness: the feeling itself.
Today’s tools mostly show access consciousness. Technology cannot yet copy or directly check what a color feels like from the inside. So, color qualia remain out of reach and might always be private.
Implications for Neuroscience and Beyond
This research is not just for academics. It could change many fields and useful technologies:
- 🧠 Brain-Computer Interfaces (BCIs) could one day understand what people see, even if they cannot communicate. This includes coma patients or people with locked-in syndrome.
- 👓 Neuroprosthetics might bring back lost color vision. They could do this by activating the right brain areas in people who cannot see colors well.
- 🤖 Artificial Intelligence systems could be trained on brain-based models to “see” color more naturally, making them better at tasks that involve seeing.
- 🧬 Checking for mental or nerve problems (like hallucinations or issues with color vision) could get more exact. They could use fMRI to decode patterns.
Understanding how color perception is shared helps us start the bigger task of “mind reading.” Not like in movies, but by rebuilding conscious states from brain data.
The Gaps: What the Study Didn’t Cover
Like all studies, Bannert and Bartels’ work has limits.
- Few colors tested: They only tested red, green, and yellow. Blue, an important color that is seen and processed differently by the brain, was left out. But evidence shows it uses different brain paths.
- Simple images: They used simple, still shapes (like rings). This is not like the complex way we see colors in the real world. Real-world color changes with movement, shadows, and what we link to objects.
- Feelings and thoughts: No tests looked at how feelings or personal meaning change how we see color or how the brain shows it.
Simply put, this research shows what color someone sees in very strict lab settings. But it does not fully look at how experience, culture, emotion, or surroundings shape color perception every day.
Looking Ahead: Can Subjective Experience Ever Be Measured?
Future studies could improve this work by adding:
- More colors, including purples, cyans, and even black and white illusions.
- Real-life scenes to test how the brain responds outside of lab settings.
- Adding thought tasks, like asking people to link colors to feelings, memories, or words. This would show how meaning changes what they see.
- Asking people for real-time reports of what they “feel” while getting scans.
These steps would bring us closer to understanding color perception. And they would also help us dig deeper into conscious human experience.
As brain science changes, the line between clear pattern finding and personal feeling might become less clear. But for now, the mystery of your red versus mine remains unsolved.
In other words, decoding your brain’s pattern can reveal what color you’re looking at. But it still cannot show us what your red feels like.
Want to learn how your brain sees the world? Keep following The Neuro Times as we figure out the puzzles of vision, how we perceive things, and the science of consciousness.
Citations
Bannert, M. M., & Bartels, A. (2025). Large-Scale Color Biases in the Retinotopic Functional Architecture Are Region Specific and Shared across Human Brains. The Journal of Neuroscience, 45(40). https://doi.org/10.1523/JNEUROSCI.2717-20.2025
Scientific American. (n.d.). A 25-Year-Old Bet About Consciousness Has Finally Been Settled. https://www.scientificamerican.com/article/a-25-year-old-bet-about-consciousness-has-finally-been-settled/
