The main problem with the ‘brain in a vat’ thought experiment

There’s a certain kind of story about nature and our place in it that says that everything we experience, everything we feel, is nothing but neural circuitry. According to one thought experiment, if I were a smart enough doctor or computer scientist, I could put your brain in a vat and connect it to some electrodes that would allow some kind of simulation of the world, and you would never know. the difference. If you get the right electrical stimulus, your brain will evoke exactly the same experiences as if you were wandering around the world in your body.

But is this ‘brain a barrel’ idea correct? Can direct experience – that most intimate and immediate sense of life and the world – really be reduced to the wiring of neurons? I don’t think the answer is at all. More importantly, the error underlying this idea is a primary example of the failure of certain philosophical perspectives on science to recognize the centrality of human experience. when doing science.

Reducing conscious experiences

This thought experiment is common in modern culture and inspires countless science fiction films and TV shows The Matrix (so great) to Altered carbon (very cool, but not so great). It also forms the basis for much-discussed ideas such as the simulation hypothesis or Boltzmann Brains. Overall, brains-in-vats (let’s abbreviate them as BIVs) illustrate a certain metaphysics of science called reductionism, in which everything we experience can be reduced to the activity of lower levels in the structural hierarchies in the physical world. Reductionism plays a major role in this The Blind Spot: Why Science Can’t Ignore the Human Experience, a new book that Marcelo Glieser, Evan Thompson and I just published. In it, reductionism is seen as a constellation of views through which direct experience is forgotten that which makes scientific activity possible. The most dramatic feature of Blind spots philosophy is when useful abstractions – drawn from scientific practice – are replaced as more real than the rich, seamless lifeworld experienced. That’s exactly what happens with BIVs.

There are a number of ways to see how the BIV idea gets things wrong, but today I’m going to draw on a nice paper that my Blind spot co-author Evan Thompson wrote with Diego Cosmelli. It’s called “Brain in a Vessel or Body in a World? Brainbound versus enactive view of experience.” Thompson and Cosmelli want us to take the BIV thought experiment seriously. What would it take to actually ‘enclose’ a brain? Any answer to this question – even one that assumes we have the best technology imaginable – must grapple with a thorny problem: the fact that the brain and body are extremely interconnected, perhaps inextricably linked.

Designing a BIV

Given that a brain is just one organ in the collection of systems we call an organism, we should provide our brains with a device that keeps them alive and functioning. Your brain would need to continually receive different substances in their exact concentrations – at the same frequency and in the same brain locations – to maintain healthy function. So we would need a very specific, highly resolved circulatory system to deliver the required substances. However, keep in mind that these substances are not released passively: it is the brain activity itself that determines where, when and how the circulatory system should perform its task. This means that our artificial circulatory system must be linked with the highest resolution to the brain and its own activity in self-regulating loops. As Thompson and Cosmelli put it, “Our life-sustaining system must support this intrinsic activity and respond to it locally and systemically at all times, independently of any external evaluation of the brain’s needs.”

However, there is more. The brain as a living organ is not only maintained externally or exogenously. The brain controls motor functions: how our body parts actually move, including our senses. So instead of a one-way street, there is a continuous sensorimotor loop: endogenously controlled movement changes the way the senses are stimulated, giving rise to new movements. The brain has to deal not only with what happens in the outside world, but also with what happens as a result of its own intrinsic activity. This activity is highly non-linear: it is not a simple outcome of whatever the sensory input is, and it must all be kept within feasible limits so that it does not disrupt the homeostasis of the healthy, functioning brain.

Taking these and other requirements together, Thompson and Cosmelli conclude that if you really want to conquer a brain, you must embody it. Your VAT would necessarily become a replacement body. Note that they do not claim that the replacement body must be flesh and blood. Instead, they show how the BIV thought experiment is self-defeating. Its fundamental idea is that neural circuits are somehow the minimal condition/structure necessary for experience. Instead, Thompson and Cosmelli demonstrate that being in a body is yourself active in the world is the minimum condition/structure necessary for experience. By beginning with the science of brains as living organs in living organisms, they demonstrate one way in which the BIV idea undermines its own logic. In other words, brains may be necessary for experience, but they are not sufficient. They are part of the holism that is the embodiment of a world – the true ‘seat’ of experience.

“We have given reasons to think that the body and brain are so dynamically involved in the causality and realization of consciousness that they are explanatorily inseparable,” Thompson and Cosmelli write.

In closing, I would like to note that these kinds of arguments are not just an academic philosophical game. There’s a steady drumbeat these days of people making strong claims for AI. Some of these claims arise directly from philosophies that inform the BIV argument. Understanding exactly where the flaws in that argument show up is one step toward ensuring that we don’t end up building a deeply flawed society built on those very flaws.