A ticklish question of self

It’s unusual for a university philosophy department to have a laboratory, especially one with artificial limbs, but the unconventional workplace of Professor Jakob Hohwy is helping him cross frontiers in understanding mind/brain function

Story and photo Brad Collis

Professor Jakob Hohwy

The ‘hypothesis-testing brain’ theory of Professor Jakob Hohwy
could shed light on mental and neurological conditions.

It takes two to tickle. We learn at an early age that you can’t tickle yourself, and usually put it aside as one of life’s little curiosities. But if you suffer a mental illness such as schizophrenia, you sometimes can tickle yourself.

Pose the question ‘why’, and you enter the world of Professor Jakob Hohwy, a philosopher working at the juncture of philosophy, psychology and neuroscience. His work has captured the attention of researchers studying consciousness and cognition.

Professor Hohwy is considered a leading thinker on the nature of perception. His work on the ‘hypothesis-testing brain’ is opening avenues of study into how we perceive reality, how we interpret and respond to sensory inputs, and possible links to the causes of mental illness or conditions  such  as autism when this process goes awry – when perception disconnects a person from aspects of reality. The essence of the ‘hypothesis-testing brain’ theory is that the brain is constantly forming hypotheses about what the external world is like, then checking them against  the reality provided  by our senses.

“It’s a constant, ceaseless function – predictions being tested against what actually happens, and then error-corrected,” says Professor Hohwy. “It may explain the basis of perception, learning and action, from birth onwards.”

Professor Hohwy says the brain needs to learn, but can do so only through sensory inputs – sight, hearing, smell, touch, taste. “So the brain has to first form internal hypotheses that are tested and corrected as actual sensory input is measured.”


Professor Hohwy’s theory and other suppositions about the role of the brain’s hypothesis testing, or ‘expectation’, are at the forefront of current mind/brain function debate, and are also crossing into the issue of whether or not we’re building computers that can think. His theory allows the brain to be considered a mathematical machine, forming statistical models and testing them against sensory evidence. This immediately leads to comparisons with ‘deep learning’ computers that are taking ‘machine learning’ to a new and already controversial level.

The question being asked is: If powerful computers can interpret and process statistical pattern recognition, undertake probabilistic planning and respond with adaptive systems – are they learning to think? Will they challenge the whole notion of consciousness?

“There is a new frontier opening up about consciousness and sensory awareness … a lot of competing views, scepticism, and also support for theories like mine,” Professor Hohwy says. “It could lead to a paradigm shift in our ‘sense of self’ as humans.”

Through this constant process the difference between the brain’s prediction of reality, and actual reality, diminishes to the point where we become confident in our personal sense of reality.

Being unable to tickle yourself is, in effect, a form of reassurance that the brain knows the difference between self and non-self. Conversely, a person suffering schizophrenia is more readily able to tickle himself or herself.

This suggests a hypothesis-testing fault where the brain is surprised by the otherwise very predictable consequences of its own actions.

In a mind-bending experiment, Professor Hohwy and colleagues demonstrated the self-tickling effect further by first creating the illusion that a person in the experiment had swapped bodies with someone else, and consequently was tickling themself with that other body. Another experiment involves a person sitting in front  of  a rubber hand with their own hand hidden from view. Both hands are touched simultaneously, but because the subject can see only the rubber hand, the mind becomes convinced it’s their real hand. If a researcher threatens the rubber hand with a sharp object, some subjects react in fright, convinced they’ll  be hurt.

Professor Hohwy is associate dean of research in Monash University’s Faculty of Arts, and deputy editor of the journal Neuroscience of Consciousness. His ‘hypothesis-testing brain’ theory has generated international excitement since it was published in a much-debated monograph, The Predictive Mind, in 2013.

Mind matters

For Professor Hohwy there’s always been a mystery about how people make sense of the world through sensory data.

“This has been a key philosophical question for me, and one that also needs neuroscience, which is why my research is multidisciplinary.

“Combining the philosophical with mainstream neuroscience opens the way to expanding our knowledge of the workings of the mind and brain, and from this the potential for clinical applications,” he says.

Discussing philosophical ideas about ‘self’ and ‘other’ in the context of the hypothesis-testing brain could throw new light on mental and neurological conditions, he says. “Could diminished or different capabilities in brain hypothesis testing and error correction be the  origin  of clinical psychiatric disorders?” he asks. “We could have an explanation for conditions that have elements of delusion, hallucination and other disconnections with reality.”

Professor Hohwy has set up an experimental lab in the philosophy department at Monash, where he tests these theories in collaboration with neuroscientists and psychiatrists. His team has helped throw light on how hypothesis testing differs in people with autism when they’re confronted with multiple conflicting sensory inputs.

We could have an explanation for those conditions that have elements of delusion, hallucination and other disconnections with reality.
Professor Jakob Hohwy

He explains how a better understanding of the hypothesis-testing brain becomes particularly relevant if some psychiatric conditions are a consequence of the brain’s learning process malfunctioning: “Could there, for example, be therapies with which to ‘unlearn’ the false interpretations  …  notwithstanding the genetic influences that we also know have a strong bearing on mental illness?” The overarching hope is that with this theory, neuroscience will be able to create more effective treatments to restore a more accurate interpretation of sensory signals.