Fading Qualia
Overview
Imagine gradually replacing a person's neurons with functionally identical silicon chips. The person remains behaviorally and cognitively identical throughout. Suppose that with each replacement, the person's qualia start to slowly fade (become weaker, dimmer, or disappear entirely). It seems absurd that someone could lose conscious experience gradually without noticing or reporting it, since their behaviour and self-reports stay constant. Therefore, functional organisation is what matters for consciousness.
Responses
Even if we accept this argument, it is possible that the necessary functions may have features that do not carry over on Turing-equivalence (i.e. might not work on digital computers) or might even involve non-computable functions (see also Church Turing Thesis and Natural Selection Argument). There are classes of theories of consciousness that draw on non-computable functions, that are nonetheless still functions. In order to replace a biological neuron with something truly functionally identical to maintain consciousness, it might need to be different from a silicon neuron in relevant ways for the CF argument in scope, e.g. it might require the ephaptic EM field effects which have been shown relevant in human brain function.
Further reading
- Chalmers D (1995). Absent Qualia, Fading Qualia, Dancing Qualia