New research provides evidence that the brain actively suppresses visual perception in the area of the visual field where a person’s own hand movement is predicted to occur.
This manipulation of our visual perception is, of course, not something we consciously experience. But thanks to the growth of virtual reality technology, researchers from the University of Tartu were able to examine whether the movement of our own hand is suppressed from our visual field. Their findings were published in the journal Neuroscience of Consciousness.
“Our research is driven by the question of how the brain works on a computational level,” one of the researchers, Madis Vasser, explained to PsyPost. “When we sense the outside world through our eyes, ears and other organs, we are constantly bombarded by a huge amount of information. Processing all of it is neither possible nor useful. So the brain must optimize its computations somehow.”
“One contemporary theory about such operations is the predictive coding paradigm. In essence, instead of constantly sampling the world and making sense of it all, it’s far more efficient for the brain to already predict the next sensory input and then just check if it the sensory info corresponds or should the model be modified. One nice example of this phenomena is the inability of people to tickle themselves, as the sensory stimulation is predicted and thus not surprising or ticklish.”
“We wanted to validate another outcome of the predictive coding theory, which postulates that in order to move your arm at all, the brain needs to inhibit the part of the visual field where the arm is moving,” Vasser continued. “Otherwise moving your arm would produce a massive prediction error. Basically, in order to move your arm, the brain does not want to know where the hand is at the moment. This brings us to the experiment under discussion.”
The researchers used an Oculus Rift virtual reality headset along with a Leap Motion hand tracking device for their experiments, which were conducted with a total of 60 participants.
The virtual reality environment consisted of oscillating spheres in an otherwise empty space. Participants were tasked with monitoring either the motion or the color of the spheres while performing a pre-trained hand movement. They were told to react as fast as possible — by clicking a mouse button — once they had found their target. The moving hand of the participant, however, was completely invisible in the VR environment.
Sometimes the target appeared behind the participant’s physical location of the participant’s hand, while other times it appeared elsewhere.
“The participants definitely all left with a new sensation of having had an invisible hand!” Vasser remarked.
The researchers found that the reaction times were slower when the target was behind the invisible hand, suggesting that the brain does in fact suppress perception in the area of the visual field where the hand movement is predicted to occur.
“Looking at the results, we can confirm that it does seem that the brain attenuates the attention in the area where the own hand is moving,” Vasser explained. “The effects are not massive, so direct takeaways to everyday life should be made with caution. A general comment would be that this effect is not a bug, it’s a feature – our attention is limited, so the more the brain can predict or do on autopilot, the more available resources it has for unpredictable situations.”
Vasser and his colleagues are planning to do more research on this topic.
“In the current paper we measured visual perception through a proxy measure, using reaction time,” he told PsyPost. “Our next experiment will probe visual perception much more directly, looking at the perception of contrast with similar methodology. As we are already using virtual reality for our experiments, we also plan to generate more ecologically valid environments to conduct the experiments.”
“It’s always important to remember the end goal. We think our work is important no matter if we get positive or negative results. In the end, this helps us to validate or reject theories about the fundamental computations in the brain. When we arrive on parsimonious model that is able to explain and predict both the normal and abnormal brain functioning, this will have a big impact on areas such as education, mental health and artificial intelligence.”
The study, “Attention is withdrawn from the area of the visual field where the own hand is currently moving“, was also co-authored by Kristjan-Julius Laak, Oliver Jared Uibopuu, and Jaan Aru.