Source: The Conversation – UK – By Renzo Lanfranco, Principal Researcher, Department of Clinical Neuroscience, Karolinska Institutet
Most of us go through the day without thinking much about our bodies – until something goes wrong. Yet beneath that apparent simplicity lies a remarkable achievement: the brain must constantly knit together sights, touches and signals from muscles and joints into a coherent sense of “this body is mine”.
Psychologists and neuroscientists call this body ownership. It is a key part of self-consciousness: the feeling of being a self located in a particular body, separate from the world around you. It’s partly what makes us different to AI.
For decades, theories have proposed that a lot of this bodily processing happens outside awareness. It’s a kind of unconscious process that quietly guides our movements while consciousness focuses on other things. Now our new study challenges this idea – giving interesting insights into theories of consciousness.
Most experiments on consciousness have used flashes of light or sounds, asking when and how these external stimuli reach awareness. Surprisingly, very little work has directly tested how conscious awareness relates to the bodily self.
Rubber hand experiments
To investigate this, we used a modern version of the famous rubber hand illusion. In this illusion, a participant’s real hand is hidden from view while a lifelike rubber hand is placed in front of them. If both hands are stroked in synchrony, most people begin to feel that the rubber hand is, strangely, part of their own body.
We built a robotic set-up that allowed us to control this illusion with millisecond precision. In our main experiment, 32 participants saw two rubber hands side by side, while a robot tapped their real, hidden hand.
On every trial, one rubber hand was tapped in perfect synchrony with the real hand and the other was tapped with a slight delay – from 18 to 150 milliseconds. After a short sequence of taps, people had to choose which rubber hand felt more like their own. Then they rated how clear that feeling was.
This gave us two things to compare. One was objective performance – how accurately people’s feeling of hand ownership could tell which hand matched their real hand’s timing. The second was subjective awareness – how clearly they reported feeling that sense of ownership.
If a lot of body ownership processing happens unconsciously, we might expect people to be more likely to pick the correct rubber hand, even when they report only a vague or unclear feeling of ownership.
Illustration by Mattias Karlén, CC BY
That is not what we found. As we increased the lack of synchrony between the real and fake hands, people became better at picking the “correct” hand. Crucially, their awareness ratings improved in lockstep.
Both objective performance and reported clarity started to rise at around 30 milliseconds of mismatch. Below that, people were essentially guessing; above that, they both chose more accurately and reported clearer feelings of ownership.
In other words, as soon as the brain started to reliably tell the difference between “my hand” and “not my hand”, people’s conscious experience reflected that difference. We did not see the common pattern reported in visual studies, where unconscious processing can occur before stimuli reach awareness.
Body ownership vs timing
To test whether this was really about body ownership – rather than simply noticing timing – we ran two control experiments. When we rotated the rubber hands into an anatomically impossible position, the illusion disappeared and people mostly reported no clear feeling of ownership, regardless of timing.
And when we replaced the hands with wooden blocks and asked people to judge simultaneity instead of ownership, their awareness no longer tracked their performance as tightly. This suggests that strong conscious access is specific to body ownership, not just to any kind of multisensory integration.
In further experiments, we asked whether the same close relationship holds when body ownership builds up gradually. In one study, we varied how many taps people received before making their choice. More taps meant more sensory evidence. As expected, their ability to discriminate ownership improved with more touches. But again, their awareness ratings improved proportionally.
Taken together, our findings point to a simple but powerful conclusion: for body ownership, consciousness seems to have continuous, privileged access to the relevant information.
This contrasts with many studies of vision and hearing, where stimuli can be processed and influence behaviour without ever entering awareness. It suggests that the bodily self may occupy a special place in our conscious lives.
One reason may be that body ownership is intrinsically self-related: it anchors a first-person perspective in space and underpins almost everything else we experience. Another is that it depends on complex integration across many senses, which may require the kind of widespread brain activation associated with conscious experience.
Implications for mental health
Understanding how body ownership and awareness are linked is not just a philosophical exercise. Distortions of bodily self-perception are common in conditions such as schizophrenia, eating disorders, borderline personality disorder and autism spectrum disorders, where people may feel alienated from their bodies or misperceive their size, shape or boundaries. Our work offers new tools to study how finely tuned the system is.
The findings also resonate with rapidly developing technologies in virtual reality and prosthetics. Many applications aim to “embody” a user in a digital or artificial body. Knowing that body ownership is tightly tied to awareness suggests that successful embodiment will depend on keeping multisensory signals aligned in a way that sustains a clear, conscious sense of “this is me”.
Finally, our results speak to big-picture theories of consciousness. If information about our own body is almost always admitted into awareness, this supports the idea that maintaining a stable, embodied self may be one of the core functions of conscious experience. This perspective ultimately highlights a key gap between humans and current artificial systems, challenging the idea that AI – at least in its current forms – could resemble human consciousness.
Renzo Lanfranco receives funding from the Swedish Research Council (Vetenskapsrådet) and the Strategic Research Area Neuroscience (StratNeuro).
– ref. Why our physical bodies may be a core part of conscious experience – new research – https://theconversation.com/why-our-physical-bodies-may-be-a-core-part-of-conscious-experience-new-research-270836
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