For most of us, it seems obvious when we are responsible for an action. If we walk, move our hands, or speak, our brain normally knows that we caused those movements. This ability is known as the sense of agency—the feeling that we are the author of our own actions.
But new research shows that this feeling can be surprisingly easy to manipulate. Using immersive virtual reality (VR), researchers demonstrated that people can experience the convincing illusion of walking through a virtual environment while their real body remains seated and almost completely motionless.
The study, led by Elena Kokkinara and colleagues, explored how the brain decides whether an action belongs to us and how virtual reality can interfere with that process.
How Does the Brain Know an Action Is Ours?
When we decide to move, the brain sends motor commands to our muscles. At the same time, it appears to generate an internal prediction of what the movement should feel and look like.
Scientists often describe this process using the idea of an efference copy. When the brain sends a command to move, a copy of that command can be used to predict the sensory consequences.
For example, if you decide to raise your hand, your brain expects to see your hand move and feel the corresponding sensations. When the predicted information matches what your senses actually receive, the brain can conclude that you caused the movement.
This process helps create our normal sense of control and responsibility over our actions.
However, researchers have discovered that the brain does not rely exclusively on actual physical movement. Visual information, expectations, previous instructions and the way we perceive our body can also influence our sense of agency.
That creates an intriguing possibility: if the brain receives convincing evidence that a body is moving, could it believe that we are performing that movement even when our real body is not moving?
Virtual Reality Can Confuse the Sense of Agency
Previous experiments have already shown that people can develop a strong feeling of ownership over virtual bodies.
In immersive VR, a participant can see a life-sized virtual body from a first-person perspective. If that virtual body moves in synchrony with the participant's real movements, the brain can begin to treat the virtual body as part of the person's own body.
Researchers have even observed situations where people attributed actions performed by another body to themselves.
These findings suggest that our sense of agency is not simply determined by muscle movements. Instead, the brain combines different sources of information—including vision, body perception, expectations and sensory feedback—to determine who is performing an action.
The new study investigated whether the same principle could be applied to something much more complex: walking.
The Walking Experiment
The researchers recruited 28 participants and placed them in an immersive virtual environment.
Importantly, the participants were actually sitting in a fixed chair. They were not physically walking. Apart from movements of their heads, their bodies remained still.
Inside VR, however, participants saw a virtual human body walking forward across a landscape.
The researchers changed two important aspects of the experience.
The first was perspective.
In the first-person perspective (1PP) condition, participants saw the virtual body as if it occupied the same position as their real body. Looking down, they could experience the virtual body as though it were their own.
In the third-person perspective (3PP) condition, the virtual body was viewed as a separate body from outside.
The second factor was head sway.
During real walking, our head naturally moves slightly with every step. The researchers recreated this movement in VR for some participants. Others experienced the virtual walking without this additional head-sway animation.
This allowed the researchers to investigate whether adding realistic movement to the viewpoint would strengthen the illusion.
What Happened When Participants Saw Themselves Walking?
The results were striking.
Participants who experienced the virtual body from the first-person perspective reported significantly stronger feelings of body ownership, agency and walking compared with participants who saw the body from the third-person perspective.
In other words, simply changing the viewpoint helped determine whether people felt that the walking virtual body was actually them.
The participants knew, at a rational level, that they were sitting in a chair. Yet their subjective experience could tell a very different story.
Their brains were receiving visual information showing a body that appeared to be their own body—and that body was walking.
The result was an illusion of agency over walking despite the absence of real walking movements.
Why Is Walking So Interesting?
Walking is different from simply moving a hand or speaking.
Normal walking involves repeated movements of both legs and produces a complex combination of sensory information. It also affects the body's balance system, including the vestibular system, which helps us detect movement and orientation.
Real walking also produces optic flow—the changing visual pattern created as the surrounding environment appears to move past us.
When we walk forward, the world seems to flow around us. VR can reproduce some of these visual cues, potentially making an artificial walking experience more convincing.
Previous research has suggested that simulated walking movements and visual feedback can produce sensations associated with locomotion, even when a person's actual body is not walking.
An Unexpected Result: Sway Reduced Agency
One of the interesting findings was related to head sway.
The researchers initially expected that adding walking-like movement to the viewpoint might make the experience feel more realistic and perhaps strengthen the illusion of walking.
However, the results showed that head sway actually reduced the reported level of agency.
This is important because it demonstrates that making an illusion more physically realistic does not necessarily make people feel more responsible for the action.
The brain appears to combine multiple sensory signals when deciding whether an action belongs to us. Adding another movement signal may sometimes make those signals less consistent rather than more convincing.
The Body Can React Even When It Isn't Moving
The researchers also measured physiological responses while participants experienced the virtual body walking uphill.
Walking uphill normally requires greater physical effort. Although the participants were not actually climbing anything, their bodies showed increased arousal during the virtual uphill experience.
This suggests that the illusion was not simply a visual trick that participants consciously imagined.
The virtual experience could produce measurable physiological changes associated with preparing for physical effort.
The findings therefore demonstrate how strongly immersive VR can influence the brain's perception of the body and its actions.
What This Reveals About Human Perception
The study provides an important insight into how the brain constructs our sense of self.
We often experience our body and actions as straightforward facts. If we move, we know we moved. If we walk, we know we are walking.
But the research suggests that this experience is actually the result of the brain continuously combining different signals.
Vision, body ownership, expectations and sensory information can all contribute to the feeling that an action belongs to us.
When these signals are manipulated in a convincing virtual environment, the brain can temporarily experience an action that the physical body is not actually performing.
Why This Could Matter Beyond VR
Understanding this process could have applications in several areas of science and medicine.
Virtual body illusions are already being investigated for rehabilitation, pain management and the study of neurological conditions involving altered body perception.
For people who cannot physically walk, virtual walking experiences could potentially provide new ways to study how the brain represents locomotion and how sensory feedback influences movement perception.
The research may also help scientists better understand conditions in which the normal relationship between intention, movement and body perception becomes disrupted.
Most importantly, the study demonstrates something fundamental about the human brain: our experience of controlling our body is constructed from sensory information rather than simply being a direct reflection of physical movement.
A person can be sitting completely still—and yet, under the right virtual conditions, their brain can make them feel as though they are walking.
Reference: Kokkinara, E., Kilteni, K., Blom, K. et al. First Person Perspective of Seated Participants Over a Walking Virtual Body Leads to Illusory Agency Over the Walking. Sci Rep 6, 28879 (2016). https://doi.org/10.1038/srep28879
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