This paper was published as a GPI working paper in March 2024.
Abstract
The Fading Qualia Argument is perhaps the strongest argument supporting the view that in order for a system to be conscious, it does not need to be made of anything in particular, so long as its internal parts have the right causal relations to each other and to the system’s inputs and outputs. I show how the argument can be resisted given two key assumptions: that consciousness is associated with vagueness at its boundaries and that conscious neural activity has a particular kind of holistic structure. I take this to show that what is arguably our strongest argument supporting the view that consciousness is substrate independent has important weaknesses, as a result of which we should decrease our confidence that consciousness can be realized in systems whose physical composition is very different from our own.
Introduction
Many believe that in order for a system to be conscious, it does not need to be made of anything in particular, so long as its internal parts have the right causal relations to each other and to the system’s inputs and outputs. As a result, many also believe that the right software could in principle allow there to be something it is like to inhabit a digital computer, controlled by an integrated circuit etched in silicon. A recent expert report concludes that if consciousness requires only the right causal relations among a system’s inputs, internal states, and outputs, then “conscious AI systems could realistically be built in the near term.” (Butlin et al. 2023: 6) If that were to happen, it could be of enormous moral importance, since digital minds could have superhuman capacities for well-being and ill-being (Shulman and Bostrom 2021).
But is it really plausible that any system with the right functional organization will be conscious - even if it is made of beer-cans and string (Searle 1980) or consists of a large assembly of people with walky-talkies (Block 1978)? My goal in this paper is to raise doubts about what I take to be our strongest argument supporting the view that consciousness is substrate independent in something like this sense.[1] The argument I have in mind is Chalmers’ Fading Qualia Argument (Chalmers 1996: 253–263). I show how it is possible to resist the argument by appeal to two key assumptions: that consciousness is associated with vagueness at its boundaries and that conscious neural activity has a particular kind of holistic structure. Since these assumptions are controversial, I claim only to have exposed important weaknesses in the Fading Qualia Argument.
I’ll begin in section 2 by explaining what the Fading Qualia Argument is supposed to show and the broader dialectical context it inhabits. In section 3, I give a detailed presentation of the argument. In section 4, I show how the argument can be answered given the right assumptions about vagueness and the structure of conscious neural activity. At this point, I rely on the assumption that vagueness gives rise to truth-value gaps. In section 5, I explain how the argument can be answered even if we reject that assumption. In section 6, I say more about the particular assumption about the holistic structure of conscious neural activity needed to resist the Fading Qualia Argument in the way I outline. I take the need to rely on this assumption to be the greatest weakness of the proposed response.
Read the rest of the paper
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See the third paragraph in section 2 for discussion of two ways in which the conclusion supported by this argument is weaker than some may expect a principle of substrate independence to be.
(EDIT: Split this up into two comments, the other here.)
I think that there's probably a minimum level of substrate independence we should accept, e.g. that it doesn't matter exactly what matter a "brain" is made out of, as long as the causal structure is similar enough on a fine enough level. The mere fact that neurons are largely made out of carbon doesn't seem essential. Furthermore, human and (apparently) conscious animal brains are noisy and vary substantially from one another, so exact duplication of the causal structure doesn't seem necessary, as long as the errors don't accumulate so much that the result isn't similar to a plausible state for a plausible conscious biological brain.[1] So, I'm inclined to say that we could replace biological neurons with artificial neurons and retain consciousness, at least in principle, but it could depend on the artificial neurons.
It's worth pointing out that the China brain[2] and a digital mind (or digital simulation of a mind, on computers like today's) aren't really causally isomorphic to biological brains even if you ignore a lot of the details of biological brains. Obviously, you also have to ignore a lot of the details of the China brain and digital minds. But I could imagine that the extra details in the China brain and digital minds make a difference.
These extra details make me less sure that we should attribute consciousness to the China brain and digital minds, but they don’t seem decisive.
From footnote 4 from Godfrey-Smith, 2023 (based on the talk he gave):
From the Wikipedia page:
(China's population, at 1.4 billion, isn't large enough for each person to only simulate one neuron and so simulate a whole human brain with >80 billion neurons, but we could imagine a larger population, or a smaller animal brain being simulated, e.g. various mammals or birds.)