Left: the white dot moves from the left to the right side of the screen in 0,5 seconds. The bottom image shows the brain activity pattern in the visual cortex, which is similar to the visual dot stimulus. Right: in another condition of the experiment, only the first dot on the left side of the screen was shown to the study participants. The right image shows how the activity pattern of the visual cortex represents not only the starting point, but all points of the full dot sequence.
Credit: Image courtesy of Radboud University
For a long time, researchers thought of the visual cortex as a brain area that determines what you perceive based on information coming from the eyes. Neuroscientists from Radboud University now show that the area is also involved in the prediction of future events. Nature Communications publishes the results on May 23.
Imagine that you are standing on the sidewalk, ready to cross the street. A car approaches and you need to decide whether to wait, or to cross the street before the car passes by. Did you ever wonder how you predict the future trajectory of the car? An experiment by Matthias Ekman and fellow researchers from Radboud University’s Donders Institute shows that the primary visual cortex, the main visual area of our brain, is not only involved in perceiving the car, but also in predicting its future locations.
The Radboud researchers designed an experiment that mimics this kind of situation. Instead of a car, study participants were shown a white dot moving quickly from the left to the right side of the screen, while lying in an fMRI scanner. The brain activity pattern in their visual cortex proved remarkably similar to the visual dot stimulus that was shown on the screen.
The crucial part of the experiment began after participants had watched the moving dot sequence for a few minutes. Now, occasionally, only the first dot on the left side of the screen was shown. Interestingly, the visual cortex’s activity pattern represented not only the starting point of the dot sequence — the one that was shown on screen — but also the remaining dots of the sequence. Ekman: “Our results show that we form expectations about upcoming events, and that the visual cortex can complete a sequence from only partial input.”
The predictive power of the visual cortex is also apparent from the results of one study condition in which participants were asked to focus on a changing letter in the background, completely ignoring the moving dots — see this video for an illustration of the task. Surprisingly, the same pattern of activity as before was measured in the visual cortex. “Your visual cortex predicts these events, even when your attention is elsewhere” according to Ekman. “The fact that the event prediction is independent from the attentional state, suggests that it reflects an automatic process.”
Of course, the MRI experiment is simplified compared to real life. But according to Ekman, the results can still tell us about how we anticipate future events in the ever changing world. “Our visual cortex might constantly predict events happening all around us on a daily basis: the rotating arms of a windmill, or how to catch the ball that is moving towards us.” In a follow-up study, the researchers examine which brain areas collaborate with the visual cortex to anticipate upcoming events. “We expect that the hippocampus — a brain area linked to memory — plays an important role in this process.”
Matthias Ekman, Peter Kok, Floris P. de Lange.Time-compressed preplay of anticipated events in human primary visual cortex. Nature Communications, 2017; DOI: 10.1038/NCOMMS15276