Tuesday 24 January 2023

‘Brain in a Vat’: A Thought Experiment

By Keith Tidman

Let’s hypothesise that someone’s brain has been removed from the body and immersed in a vat of fluids essential for keeping the brain not only alive and healthy but functioning normally — as if it is still in a human skull sustained by other bodily organs.

A version of this thought experiment was laid out by René Descartes in 1641 in the Meditations on First Philosophy, as part of inquiring whether sensory impressions are delusions. An investigation that ultimately led to his celebrated conclusion, ‘Cogito, ergo sum’ (‘I think, therefore I am’). Fast-forward to American philosopher Gilbert Harman, who modernised the what-if experiment in 1973. Harman’s update included introducing the idea of a vat (in place of the allegorical device of information being fed to someone by an ‘evil demon’, originally conceived by Descartes) in order to acknowledge the contemporary influences of neuroscience in understanding the brain and mind.

In this thought experiment, a brain separated from its body and sustained in a vat of chemicals is assumed to possess consciousness — that is, the neuronal correlates of perception, experience, awareness, wonderment, cognition, abstraction, and higher-order thought — with its nerve endings attached by wires to a quantum computer and a sophisticated program. Scientists feed the disembodied brain with electrical signals, identical to those that people are familiar with receiving during the process of interacting through the senses with a notional external world. Hooked up in this manner, the brain (mind) in the vat therefore does not physically interact with what we otherwise perceive as a material world. Conceptualizations of a physical world — fed to the brain via computer prompts and mimicking such encounters — suffice for the awareness of experience.

The aim of this what-if experiment is to test questions not about science or even ‘Matrix’-like science fiction, but about epistemology — queries such as what do we know, how do we know it, with what certainty do we know it, and why does what we know matter? Specifically, issues to do with scepticism, truth, mind, interpretation, belief, and reality-versus-illusion — influenced by the lack of irrefutable evidence that we are not, in fact, brains in vats. We might regard these notions as solipsistic, where the mind believes nothing (no mental state) exists beyond what it alone experiences and thinks it knows.

In the brain-in-a-vat scenario, the mind cannot differentiate between experiences of things and events in the physical, external world and those virtual experiences electrically prompted by the scientists who programmed the computer. Yet, since the brain is in all ways experiencing a reality, whether or not illusionary, then even in the absence of a body the mind bears the complement of higher-order qualities required to be a person, invested with full-on human-level consciousness. To the brain suspended in a vat and to the brain housed in a skull sitting atop a body, the mental life experienced is presumed to be the same.

But my question, then, is this: Is either reality — that for which the computer provides evidence and that for which external things and events provide evidence — more convincing (more real, that is) than the other? After all, are not both experiences of, say, a blue sky with puffy clouds qualitatively and notionally the same: whereby both realities are the product of impulses, even if the sources and paths of the impulses differ?

If the experiences are qualitatively the same, the philosophical sceptic might maintain that much about the external world that we surmise is true, like the briskness of a winter morning or the aroma of fresh-baked bread, is in fact hard to nail down. The reason being that in the case of a brain in a vat, the evidence of a reality provided by scientists is assumed to resemble that provided by a material external world, yet result in a different interpretation of someone’s experiences. We might wonder how many descriptions there are of how the conceptualized world corresponds to what we ambitiously call ultimate reality.

So, for example, the sceptical hypothesis asserts that if we are unsure about not being a brain in a vat, then we cannot disregard the possibility that all our propositions (alleged knowledge) about the outside physical world would not hold up to scrutiny. This argument can be expressed by the following syllogism:

1. If I know any proposition of external things and events, then I know that I am not a brain in a vat;

2. I do not know that I am not a brain in a vat;

3. Therefore, I do not know any proposition of external things and events about the external world.

Further, given that a brain in a vat and a brain in a skull would receive identical stimuli — and that the latter are the only means either brain is able to relate to its surroundings — then neither brain can determine if it is the one bathed in a vat or the one embodied in a skull. Neither mind can be sure of the soundness of what it thinks it knows, even knowledge of a world of supposed mind-independent things and events. This is the case, even though computer-generated impulses realistically substitute for not directly interacting bodily with a material external world. So, for instance, when a brain in a vat believes that ‘wind is blowing’, there is no wind — no rushing movement of air molecules — but rather the computer-coded, mental simulation of wind. That is, replication of the qualitative state of physical reality.

I would argue that the world experienced by the brain in a vat is not fictitious or unauthentic, but rather is as real to the disembodied brain and mind as the external, physical world is to the embodied brain. Both brains fashion valid representations of truth. I therefore propose that each brain is ‘sufficient’ to qualify as a person: where, notably, the brains’ housing (vat or skull) and signal pathways (digital or sensory) do not matter.


Martin Cohen said...

Thandks for this classic exploration Keith. Is the idea here that "premise 2" is clearly "true"? That " I do not know that I am not a brain in a vat". I would say we do know such things. There is a 'doubt' but too small to be taken further. Descartes says logical truths have a higher status – but that seems to be simply "false". There are different, incompatible logics. How do we know which one applies? Later on in the Meditations, Descartes says God would not play tricks on us. That seems a dubious reassurance too!

Keith said...

As for premise 2, Martin, I regard the ‘vat’ metaphorically, just as today no one takes Descartes’ ‘evil demon’ as literal. Vats and evil demons are useful metaphors; however, to my mind, vats stand in for the existence of ‘alternative realities’. With shades, perhaps, of George Berkeley advocating that ‘perception’ and ‘being’ are bonded.

In the case of the vat, the metaphor mirrors how differently, qualitatively, each of us experiences reality — according to one’s own circumstances, and in line with the differences in how stimuli are received and interpreted to shape one among innumerable alternative, equally valid realities.

The preceding notion definitionally discounts, then, the concept of a single, objective reality, shared by everyone. As if my experience of physical, external reality, like the greenness of a leaf, is in no manner different than someone else’s experience of greenness. I suggest our ‘vats’ — our experiences of reality — greatly differ qualitatively.

But, because neuroscientists and philosophers of mind don’t yet understand how all that works conceptually or neurobiologically — one such consequential challenge being to get our arms around human consciousness — premise 2 is arguably true, on a metaphorical level. To that extent, Harman’s ‘vat’ and Descartes’ ‘evil demon’ are handy devices to weave narrative threads.

Martin Cohen said...

Heh, well, you are on safe ground with "greeness"! It's accepted that some people see it as "red" - while dogs and cats only see browny colours. But ifyou think you do know you are not a brain in a vat, then you re surely collapsing the whole argument?

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