So, which film did your brain see? – Justus Liebig University Giessen

Nr. 134 • 3. September 2024 (english version)

Two people are sitting in the cinema and looking at the screen: Do they see the same thing? Or is the film in their heads different? Researchers at the Justus Liebig University Giessen (JLU) have discovered that each brain experiences its own version of the film and published their results in the journal “Proceedings of the National Academy of Sciences” (PNAS). In fact, each viewer has a slightly different version of the film in their head – and these differences can be predicted by the individual eye movements.

Feet, hands, noses, ears – human bodies are always made up of the same parts, but their anatomy differs from person to person. This also applies to the brain and its activity patterns. Neuroscientists use functional magnetic resonance imaging and machine learning to make these brain activities comparable. These techniques have made it possible to “translate” activity patterns between different brains for about a decade.

Petra Borovska and Prof. Dr. Ben de Haas from the Department of General Psychology at Justus Liebig University Giessen (JLU) used this technology to study the consequences of individual eye movements. They analyzed how well one person’s brain activity could be predicted based on the activity of another person while 19 volunteers watched the same film – either freely or while passively looking at the center of the screen. Natural eye movements led to significantly stronger activations in the visual centers of the brain compared to passive observation. However, these activations were so individual that it became more difficult to transfer brain activity from one person to another.

“Eye movements were traditionally considered a simple reaction to what is happening in front of our eyes,” explains de Haas. “But we now know that this is not everything. Eye movements are as individual as personality traits. Some people focus more on faces, others on text or other details.” Borovska adds: “We suspected that these individual gaze habits lead to a unique world in people’s heads. Now we know: That’s true! We were even able to predict how much the brain activity patterns differ between two people when we recorded the similarity of their eye movements in a separate experiment, several days apart. It is amazing that eye movements lead to stronger neural activity, but at the same time make these activity patterns less comparable. Normally a stronger signal means clearer data, but here the signal – the neural representation of the film – is different, a kind of director’s cut of the individual brain.”

The team is currently studying how eye movements develop over the course of life and how they affect our understanding of scenes and everyday tasks. “There is still so much to discover,” says de Haas. “You can even ask the person sitting next to you in the cinema: ‘What film did you see?'”

Petra Borovska, Benjamin de Haas: Individual gaze shapes diverging neural representations, Proceedings of the National Academy of Sciences (PNAS), August 30, 2024, 121 (36)

Prof. Dr. Ben de Haas, Petra Borovska
Department of General Psychology at JLU
benjamin.de-haas
petra.borovska

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