Do We All See Red the Same Way?

When you and I both look at a stop sign, is your red the same as mine?

Scientists have argued about this for decades.

Researchers at the University of Tübingen have now discovered that brain responses to color are not entirely personal, and patterns of activity in early and mid-level visual areas are consistent across people.

Brain regions and their unique color biases

Color is central to how we perceive the world. It can guide recognition, memory and emotion (for example, seeing a particular shade of red and yellow may evoke feelings of hunger for French fries).

For a long time, researchers thought color was handled in a few specialist patches in the brain, such as the “blobs” in V1 or the “globs” in V4. However, the eye itself doesn’t treat color evenly. Cone cells are bunched at the centre of the retina and sparser at the edges, which means sensitivity shifts across our visual field. Behavioral tests have found that people are better at seeing some colors in some parts of their vision compared with others.

Brain imaging studies have demonstrated that it’s possible to decode which color someone is looking at from their brain activity. However, those decoders only worked when trained and tested on the same person. This raises the question: are our brain responses to color personal, or do they follow the same pattern across people?

Dr. Michael Bannert, a postdoctoral researcher, and Dr. Andreas Bartels, a professor of visual neuroscience, from the University of Tübingen, set out to address this in their latest study. They wanted to know whether those shared signatures exist and whether different brain areas show their own quirks in handling color.

Decoding color from shared brain activity

The study involved 15 adults with normal color vision. The researchers used functional MRI (fMRI) to track brain activity as the participants looked at red, green or yellow rings. To keep them engaged, the rings occasionally flickered in brightness and the volunteers pressed a button whenever they noticed the change.

Before showing any colors, Bannert and Bartels mapped each person’s visual system to chart how different parts of the brain responded to different parts of visual space. Those maps were then aligned across people using a statistical tool.

The key idea was to build a “common response space” based on spatial patterns alone, without touching color data. This approach allowed the team to compare brain activity patterns across people without relying on individual differences in brain anatomy.

They trained a computer model to guess colors from brain activity using data from all participants, except one. The model was then used to predict what color the left-out participant was seeing.

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Within each person, the computer could reliably identify the colors and brightness they were seeing. It also worked across people, with the model able to predict what color someone else was looking at, without being trained using that individual's data.

Different brain regions also showed their own color preferences. For example, in one area, locations close to the centre of vision leaned toward yellow, while the periphery leaned toward red. These patterns were consistent across participants.

Color processing in the brain

The results suggest that color perception isn’t entirely private after all. While individual experiences of red or yellow may vary, the underlying brain patterns are similar across people, hinting at a shared neural basis for color perception. This may suggest that color processing is tied to spatial maps in the cortex rather than floating free in specialist spots.

“We can’t say that one person’s red looks the same as another person’s red. But to see that some sensory aspects of a subjective experience are conserved across people’s brains is new,” said Bannert.

However, the study is limited by size, since only 15 people took part and they all had normal color vision. The experiments also tested only three colors at two brightness levels, and fMRI only measures activity over millimeters of tissue, which may miss the fine detail of how neurons code color.

Larger and more varied groups of participants could reveal how much these shared signatures hold up across age, culture or individual differences in vision.

Reference: Bannert M, Bartels A. Large-scale color biases in the retinotopic functional architecture are region specific and shared across human brains. JNeurosci. 2025. doi: 10.1523/JNEUROSCI.2717-20.2025