It's not just a question of adding complexity. We already know that the brain is not just complex; there is a large number of brain areas that are functionally specific and connected together in specific ways.
I don’t know how this isn’t the same thing as saying added complexity. These different areas of the brain are responsible for different functions in an individual way, and then at a later stage everything is reassembled into a coherent whole. But all of these functional dependent regions could also exist for qualia zombies too, they too would require a ton of different sensory mechanisms in order to avoid running across a busy street 1 second too early or too late, or to chop a carrot without chopping off a fingertip, etc. But we don’t escape the privileged 1st person information problem, we can’t know via brain functions if a person who cut their finger instead of the carrot really feels the pain or if they are just going through the motions and acting like they are in pain. THAT their brain mechanisms matches what my brain mechanisms look like when I feel pain is an objective FACT, but whether or not the pain experience itself is being faked or is genuine in that person is unfortunately reduced to an inference. It’s this reduced quality of knowledge that is the explanatory gap when moving from the physiological data to the assurance that we don’t have a qualia zombie.
We also know that specific damage to these areas or their inter-connections causes specific deficits in consciousness, affect, and sense of self.
Such deficits in motor function ability, speech, etc, would be objective facts. But lost consciousness, and sense of self could come or could still remain without us knowing for sure. It’s like the argument about whether a coma patient can hear & understand you (or even more precisely could THIS coma patient here you, or how about THAT coma patient?). There’s no such argument about the coma patient’s brain scans.
We also have tentative models for how the supporting framework for high-level consciousness functions, from internal and external senses to hind-brain structures to mid-brain structures and on to the cortex. These models are broadly based on the evolutionary sequence that produced the mammalian brain.
I do not disagree that higher states of consciousness are an easy inference to make since we have tons of test subjects to verify that higher level functions in the cortex relates to mental states that don’t exist for lower level entities such as those with just hindbrains. But it’s that “What is it like to be a bat” problem. A friend of mine once made the claim that sharks have to be the most miserable creatures on Earth because of their disturbed & lousy sleep patterns. Now what if I made the argument that sharks live in a state of bliss? We know that levels of distress and contentness in organisms are real properties in reality (and sharks might also feel nothing at all), but to answer this shark debate a hard science can never help us (even though each individual shark would know the answer), we would be reduced to some soft science like Behaviorism to just make an inference. Unanswerable questions about reality (questions that we know for sure HAVE answers) that can’t be answered by the tools of hard physical sciences to me reveals that more exists in reality than the physical. Because we just became forced into a situation where we can only use a tool of mental language to describe a part of reality that we know is real…and that is the claim, that there’s a mental fabric of reality that falls outside of the scope of physical reality (although they are both intimately entangled, and dependent on each other).
Given what we know now, and the advances in exploratory techinques in recent years, it is not unreasonable to suggest that we may eventually be able to identify all the functional requirements (i.e. processes and information inputs) and relations necessary to result in subjective experience. Whether we will be able to say precisely how they do so is a moot point, but we should have a better understanding of it than we do now. Ultimately, it may be that we'll only be able to say that if you connect these processes together in this way and feed it this kind of information, the system will have subjective experience.
Yeah I think so too, kind of like a lie detector test but with way more information. Well that’s if we don’t kill ourselves first and have to start over with sticks & stones. Some of these stories about the record droughts, temperatures, water scarcity, floods, etc are weirding me out.