The first step of ghost-busting was recreating the ghost. Researcher Olaf Blanke conducted an experiment that would trigger the awareness of an apparition in his test subjects. He instructed blindfolded and ear-plugged participants to move their hands freely while a robotic device mimicked their movements as it touched them on the back.
When the experiment was conducted in real time, the test subjects received the disconcerting impression that they were touching themselves. But when the touch was delayed even by a few milliseconds, the participants failed to recognize that the robotic hand was moving on their command. Instead they felt another presence touch them, as well as counting a higher number of presences in their proximity compared to when the experiment was conducted in real time. Some were so affected that they decided not to continue the experiment.
The catch lies in the spatial and temporal discrepancies. The delay in the robotic hand distorted temporal and spatial perceptions, preventing integration of copy signals from the sensorimotor system in the frontparietal cortex crucial for “normal bodily experience”. The mismatch between their movements (motor signals) and touch (sensory input) distorts the perception of one’s body in the brain. The disturbance in the brain mechanisms that generate the sense of self-awareness leads to the illusion that someone else was behind them.
The discovery goes far beyond ghosts, however (and I never thought I'd say that). Having the occasional vague fear of a presence is not uncommon, but is only a slight inconvenience compared to distressful hallucinatory symptoms suffered by patients of certain neurological conditions such as schizophrenia or Alzheimer’s disease. Blanke’s primary aim with the research was to better understand these symptoms. He designed the experiment after studying the brain patterns of 12 FoP patients, discovering that hallucinations were linked to lesions in the insular, temporoparietal, and frontoparietal cortex — and the resulting asynchrony in sensorimotor signals. The robotic system “mimics the sensations of some patients with mental disorders or of healthy individuals under extreme circumstances”, Blanke explained.
Blanke expressed the hope that he could utilize this information to create another similar robotic system to achieve the opposite effect: instead of producing psychotic symptoms in healthy subjects, reverse the concept to reduce psychotic symptoms in patients. He tentatively envisions a wearable device in the future, perhaps integrated into their clothes.
Neuroscientists are advancing towards a possible therapy for hallucinations. However, there is no guarantee that alleviating the hallucinatory symptoms would be as straightforward as simply creating the opposite of the FoP-inducing robotic system. At least we now know that ghosts may simply have been the product of conflicting sensorimotor signals – it’s one less thing keeping me up at night.