How the Body Knows What Belongs to It

At CITEC, Dr. Xaver Fuchs conducts research on body perception

Dr. Xaver Fuchs’ work addresses how we know what belongs to our body and what does not – and how this occurs. The psychologist’s basic research at Bielefeld University’s Cluster of Excellence Cognitive Interaction Technology (CITEC) and the Faculty of Psychology and Sports Science could contribute to the development of better prostheses, among other things.

One classic attempt to investigate the representation of the body is an experiment with a rubber hand. Does the foot you see on the floor actually belong to your own body? Where does the pinkie finger end, and where does the table that the finger is lying on begin? At the Cluster of Excellence CITEC, psychologist Dr. Xaver Fuchs investigates how the human brain determines where the boundaries of its own body are located.

“We know that the brain generates a model of the body,” says Fuchs. In this process, different areas in the brain represent individual parts of the body. The cerebral cortex thus contains a kind of map of the body, which is involved in processing sensations and controlling movements. In contrast, other areas in the brain determine what the brain considers to be its body and what it considers to be its environment – and where the body and its constituent parts are respectively located in space.
In order to generate this map of the body, the brain needs a great deal of information about the different parts of the body. “Here, sensory processing in particular plays a role,” says Fuchs. “We know that the brain makes certain assumptions about what belongs to the body. How the brain arrives at these assumptions, however, remains largely unclear.” This is one aspect of Xaver Fuch’s research.

Furthermore, this model in the brain is not set in stone: the brain is able to adapt to changes. This is called plasticity and it comes into play, for instance, when someone undergoes an amputation of an arm or a leg.

The brain always attempts to piece together all sensory input into a coherent image of the body. If the left arm is suddenly missing, then the sensory input that would normally come from there is also missing. Researchers hypothesize that phantom pain can occur after an amputation due to neuronal mismatches that are expressed in a modification of the brain’s map of the body. Fuchs is also investigating this topic.

But what does this look like in practical terms? One classic attempt to investigate the representation of the body is an experiment with a rubber hand. Here, a test subject sits at a table and only sees one of his or her hands – the other is obscured from view. Instead, a deceptively real rubber hand lies on the table.

Next, both hands are stroked with a paint brush. This reveals that study participants often feel as though this stroking is felt in the rubber hand. “The experiment demonstrates how quickly the brain adapts to input from the environment,” explains Fuchs.

In another one of his experiments, study participants are supposed to move handles that are hidden under a rectangular surface. During this, a very a subtle force acts on the arms, which is not able to be perceived by the test subjects. “This is mainly about the localization of the body in space,” says Fuchs.

Dr. Fuchs also conducts research on people suffering from chronic pain. “Pain can influence actions,” says Fuchs. The assumption here is that the body learns to avoid certain movements if they are associated with pain. “This then results in results in avoidance or compensatory movements,” says Fuchs, “in the long term, however, this can have adverse consequences if it leads to inappropriate weight-bearing and strain.”
Fuchs does basic research, the findings of which could be important not only for virtual reality and robotics – when it comes to whether the physical self can be applied, for instance, to an avatar or a robot – but also for prosthetics. “I hope that prosthetics also benefits from this,” says Fuchs. In the future, for example, prostheses that amputees could perceive better than conventional prostheses would ideally be developed – meaning that amputees would perceive their prosthesis not as a foreign object, but as a part of their own body.

Dr. Xaver Fuchs conducts research on the body and its perception of itself.Dr. Xaver Fuchs (b. 1983) studied psychology at the Philipps University of Marburg, where he earned his degree (Diplom). He then completed his doctoral work at Department of Cognitive and Clinical Neuroscience at the Central Institute of Mental Health in Mannheim. Since 2017, he has been a research associate at the Faculty of Psychology and Sports Science at Bielefeld University and conducts research on the representation of the body and the perception of pain at the Cluster of Excellence CITEC.     

More information is available online at:

Xaver Fuchs
Biopsychology & Cognitive Neuroscience
Faculty of Psychology and Sports Science
Telephone: 0521 106 67 531

Article author: Maria Berentzen