The “rubber hand” illusion was first described in 1998.

Under the illusion, people feel that a rubber hand placed on the table before them is their own, a bizarre but convincing shift in perception that is accompanied by a sense of disowning their real hand.

Ian Sample, “‘Rubber hand illusion’ reveals how the brain understands the body” at The Guardian (2016 10 20)

Starting life as a party trick, this lecture-room favorite has been cited in over 5000 articles since. According to New Scientist in 2009, it was “hugely important in understanding how sight, touch and “proprioception” – the sense of body position – combine to create a convincing feeling of body ownership, one of the foundations of self-consciousness.” Back then, we heard,

In recent years that understanding has been explored further using increasingly freaky illusions. “The rubber hand illusion really inspired people,” says Henrik Ehrsson, a neuroscientist at the Karolinska Institute in Stockholm, Sweden. He is one of many researchers who have taken the illusion and run with it, creating a whole new set of “bodily illusions” that mess with our sense of self in strange and disturbing ways. “We’re doing all kinds of crazy stuff,” he says.

Body illusions: Rubber hand illusion” at New Scientist (18 Mar 2009)

To judge by a 2020 article at Nature, many are sure of the illusion’s usefulness today, although good reason was found to question the truism in 2011.

And now, a pin in the balloon:

In a new research paper Dr Peter Lush, Research Fellow at the Sackler Centre for Consciousness Science at the University of Sussex, demonstrates that the control conditions typically used in the Rubber Hand Illusion do not do they job they need to do.

His results show that the commonly reported effects of the Rubber Hand Illusion can be attributed to imaginative suggestion’ — otherwise known as ‘hypnosis’.

Last year Dr Lush and colleagues reported in a paper, currently under peer review but available as a preprint on PsyArxiv, substantial correlations between response to the Rubber Hand Illusion and response to imaginative suggestion , or phenomenological control, in a large sample of 353 participants. This study shows that response to the Rubber Hand Illusion is, partially or entirely a suggestion effect.

Psychologists have long been aware of the dangers of ‘demand characteristics’ — in which subjects, often without realising it, say what they implicitly think they ought to say.

Dr Lush’s work takes these concerns much further by showing that how suggestible someone is can dramatically influence what people report in the Rubber Hand Illusion — and potentially in many other experiments too.

University of Sussex, “Flaw in Rubber Hand Illusion raise tsough questions for psychology” at ScienceDaily

Is it relevant that the Rubber Hand originated as a party room illusion, where the fun of the moment depends on the success—in at least some part—of the illusion? (In hushed tones: “Oh, don’t be such a spoilsport! Go along with it!”)

Participants were provided with information about the Rubber Hand Illusion procedure (including a text description and a minute-long video demonstration of the illusion) and then asked to fill out a standard questionnaire on what they would expect to happen if they were a participant in the procedure.

Strikingly, people expect the same pattern of results that is typically found in Rubber Hand Illusion studies, both for the ‘experimental’ conditions and the ‘control’ conditions.

University of Sussex, “Flaw in Rubber Hand Illusion raise tsough questions for psychology” at ScienceDaily

It sounds as though too many people know too much about what to expect for any raw data about human cognition to be recovered from the Rubber Hand illusion.

Studies of the mind are vexed by two problems: One is discomfort over undisputed facts that point to the mind’s immaterial nature and the other is eagerness to believe simple, usually material, explanations.

For example, one of the best established facts in medicine is the very well attested placebo effect (people start to get better because they believe they will). Placebos even work for people who know that the pills are inert. It is so important to them to be part of a believing community that their physical health improves anyway. What that really shows is that our minds are not illusions but rather active, if immaterial, participants in our lives.

If the “rubber hand” goes the way of so many truisms in social psychology, it might remind us of the “lecture room psychopath,” railway worker Phineas Gage (1823–1860). In 1848, he received a catastrophic brain injury (he survived an accident in which a tamping rod was driven through his head). The story, often a staple of introductory psychology, was that his personality totally changed after the accident, perhaps in support of a “frontal lobe” theory of personality (= you are your frontal lobes).

But that canonical story is based on partial evidence. Gage’s life history is much more complex. After a period of distracted wandering, he got a job and settled down, despite the discomfort many must have felt at his disfigurement:

The drastic discontinuity was not so much between Phineas Gage pre- and post-tamping rod but between Phineas Gage (1823-1860) and the lecture room legend.

What we can learn from contemporary accounts of Gage’s post-trauma life is this: For a while after the accident, he drifted, and even ended up briefly in P. T. Barnum’s freak show, exhibiting himself and the tamping rod. But he then settled down and worked a year and a half in a stable. Later, he went with a friend to Valparaiso in Chile where he cared for horses and drove a coach and six for eight years.

Kotowicz points out the obvious,

“Working in stables is not a job for a psychopath. Horses are very sensitive and they require discipline and calm; they have to be attended to regularly, seven days a week, and work begins early.”

(They are also apt to bite, kick, rear, and stampede, if startled or abused.)

Of course, Gage had been catastrophically injured, and about twelve years later, the effects caught up with him. By February 1860, back from Chile, he continued to try to work on farms while living with or near his mother, who had moved to San Francisco. But he began to have frequent epileptic convulsions. They worsened, and he died on May 21, 1860. No autopsy was performed, but Harlow later exhumed the body and recovered Gage’s skull and the tamping rod.

Denyse O’Leary, “Phineas Gage: Evolution of a lecture room psychopath” at Uncommon Descent

There are enduring current mysteries of the mind, like the placebo effect—which hints at the mind’s immaterial nature. But there are also efforts, like the “lecture room psychopath” version of Phineas Gage, to seize on a specific relationship between the mind and the brain, making the part an explanation for the whole. Over time, these simplifications and occasional deceptions fray; the living, sometimes contradicting connections between our minds and reality are exposed. It’s still an ocean in there.

We should not be surprised if the “rubber hand” illusion must be strongly qualified in future. Like so many Psych 101 theories, it is just too pat, too static, to provide much insight into the dynamic reality of the human mind.

Further reading: Science points to an immaterial mind. If one did not start with a materialist bias, materialism would not be invoked as an explanation for a whole range of experiments in neuroscience (Michael Egnor)