I agree with 1. I think it weakens the force of the argument, but I’m not sure it defeats it.
2 might be a crux. I might say that unity is largely illusory and integration comes in degrees (so it’s misleading to count consciousnesses with integers) since we can imagine cutting connections between two regions of a brain one at a time (e.g. between our two hemispheres), and even if you took distinct conscious brains and integrated/unified them, we might think the unified brain would matter at least as much as the separate brains (this is Shulman’s thought experiment).
There could also be hidden qualia. There may be roughly insect brains in your brain, but “you” are only connected to a small subset of their neurons (or only get feedforward connections from them). Similarly, you could imagine connecting your brain to someone else’s only partially so that their experiences remain mostly hidden to you.
Maybe a better real-world argument would be split-brain patients? Is it accurate to say there are distinct/separate consciousnesses in each hemisphere after splitting, and if that’s the case, shouldn’t we expect their full unsplit brain to have at least roughly the same moral weight as the two split brains, even though it’s more unified (regardless of any lateralization of valence)? If not, we’re suggesting that splitting the brains actually increases moral weight; this isn’t a priori implausible, but I lean against this conclusion.
In particular, this suggests (assuming a causal role, with more neurons that are responsive causing more intense experiences) that if we got rid of neurons in these regions and so had fewer of them (and therefore fewer of them to be responsive), we would decrease the intensities of the experiences (and valence).
Thanks for engaging so deeply with the piece. This is a super complicated subject, and I really appreciate your perspective.
I agree that hidden qualia are possible, but I’m not sure there’s much of an argument on the table suggesting they exist. When possible, I think it’s important to try to ground these philosophical debates in empirical evidence. The split-brain case is interesting precisely because there is empirical evidence for dual seats of consciousness. From the SEP entry on the unity of consciousness:
In these operations, the corpus callosum is cut. The corpus callosum is a large strand of about 200,000,000 neurons running from one hemisphere to the other. When present, it is the chief channel of communication between the hemispheres. These operations, done mainly in the 1960s but recently reintroduced in a somewhat modified form, are a last-ditch effort to control certain kinds of severe epilepsy by stopping the spread of seizures from one lobe of the cerebral cortex to the other. For details, see Sperry (1984), Zaidel et al. (1993), or Gazzaniga (2000).
In normal life, patients show little effect of the operation. In particular, their consciousness of their world and themselves appears to remain as unified as it was prior to the operation. How this can be has puzzled a lot of people (Hurley 1998). Even more interesting for our purposes, however, is that, under certain laboratory conditions, these patients seem to behave as though two ‘centres of consciousness’ have been created in them. The original unity seems to be gone and two centres of unified consciousness seem to have replaced it, each associated with one of the two cerebral hemispheres.
Here are a couple of examples of the kinds of behaviour that prompt that assessment. The human retina is split vertically in such a way that the left half of each retina is primarily hooked up to the left hemisphere of the brain and the right half of each retina is primarily hooked up to the right hemisphere of the brain. Now suppose that we flash the word TAXABLE on a screen in front of a brain bisected patient in such a way that the letters TAX hit the left side of the retina, the letters ABLE the right side, and we put measures in place to ensure that the information hitting each half of the retina goes only to one lobe and is not fed to the other. If such a patient is asked what word is being shown, the mouth, controlled usually by the left hemisphere, will say TAX while the hand controlled by the hemisphere that does not control the mouth (usually the left hand and the right hemisphere) will write ABLE. Or, if the hemisphere that controls a hand (usually the left hand) but not speech is asked to do arithmetic in a way that does not penetrate to the hemisphere that controls speech and the hands are shielded from the eyes, the mouth will insist that it is not doing arithmetic, has not even thought of arithmetic today, and so on—while the appropriate hand is busily doing arithmetic!
So I don’t think it’s implausible to assign split-brain patients 2x moral weight.
I also think it’s possible to find empirical evidence for differences in phenomenal unity across species. There’s some really interesting work concerning octopuses. See, for example, “The Octopus and the Unity of Consciousness”. (I might write more about this topic in a few months, so stay tuned.)
As for the paper, it seems neutral between the view that the raw number of neurons firing is correlated with valence intensity (which is the view I was disputing) and the view that the proportional number of neurons firing (relative to some brain region) is correlated with valence intensity. So I’m not sure the paper really cuts any dialectical ice. (Still a super interesting paper, though, so thanks for alerting me to it!)
As for the paper, it seems neutral between the view that the raw number of neurons firing is correlated with valence intensity (which is the view I was disputing) and the view that the proportional number of neurons firing (relative to some brain region) is correlated with valence intensity. So I’m not sure the paper really cuts any dialectical ice. (Still a super interesting paper, though, so thanks for alerting me to it!)
One argument against proportion mattering (or at least in a straightforward way):
Suppose a brain responds to some stimuli and you record its pattern of neuron firings.
Then, suppose you could repeat exactly the same pattern of neuron firings, but before doing so, you remove all the neurons that wouldn’t have fired anyway. By doing so, you have increased the proportion of neurons that fire compared to 1.
I think 1 and 2 should result in the exact same experiences (and hence same intensity) since the difference is just some neurons that didn’t do anything or interact with the rest of the brain, even though 2 has a greater proportion of neurons firing. The claim that their presence/absence makes a difference to me seems unphysical, because they didn’t do anything in 1 where they were present. Or it’s a claim that what’s experienced in 1 depends on what could have happened instead, which also seems unphysical, since these counterfactuals shouldn’t change what actually happened. Number of firing neurons, on the other hand, only tracks actual physical events/interactions.
I had a similar discussion here, although there was pushback against my views.
This seems like a pretty good reason to reject a simple proportion account, and so it does seem like it’s really the number firing that matters in a given brain, or the same brain with neurons removed (or something like graph minors, more generally, so also allowing contractions of paths). This suggests that if one brain A can be embedded into another B, and so we can get A from B by removing neurons and/or connections from B, then B has more intense experiences than A, ignoring effects of extra neurons in B that may actually decrease intensity, like inhibition (and competition?).
I think 1 and 2 should result in the exact same experiences (and hence same intensity) since the difference is just some neurons that didn’t do anything or interact with the rest of the brain, even though 2 has a greater proportion of neurons firing. The claim that their presence/absence makes a difference to me seems unphysical, because they didn’t do anything in 1 where they were present.
I’m unclear why you think proportion couldn’t matter in this scenario.
I’ve written a pseudo program in Python below in which proportion does matter, removing neurons that don’t fire alters the experience, and the the raw number of neurons involved is incidental to the outputs (10 out of 100 gets the same result as 100 out of 1000) [assuming there is a set of neurons to be checked at all]. I don’t believe consciousness works this way in humans or other animals but I don’t think anything about this is obviously incorrect given the constraints of your thought experiment.
One place where this might be incorrect is by checking if a neuron was firing, this might be seen as violating the constraint on the inactive neurons actually being inactive. But this could be conceived a third group of neurons checking for input from this set. But even if this particular program is slightly astray, it seems plausible an altered version of this would meet the criteria for proportion to matter.
def experience_pain(nociceptive_neurons_list):
# nociceptive_neurons_list is a list of neurons represented by 0's and 1's, where 1 is when an individual neuron is firing, and 0 is not
proportion_of_neurons_firing = proportion_of_neurons_firing(nociceptive_neurons_list)
if proportion_of_neurons_firing < 0.3:
return pain_intensity(1)
elif proportion_of_neurons_firing > 0.3 && proportion_of_neurons_firing < 0.6:
return pain_intensity(2)
elif proportion_of_neurons_firing > 0.6 && proportion_of_neurons_firing < 1:
return pain_intensity(5)
elif proportion_of_neurons_firing == 1:
return pain_intensity(10)
else:
return pain_intensity(0)
def proportion_of_neurons_firing(nociceptive_neurons_list):
num_neurons_firing = 0
for neuron in nociceptive_neurons_list:
if neuron == 1:
num_neurons_firing += num_neurons_firing # add 1 for every neuron that is firing
return num_neurons_firing/get_number_of_pain_neurons(nociceptive_neurons_list) #return the proportion firing
def get_number_of_pain_neurons(nociceptive_neurons_list):
return len(nociceptive_neurons_list) # get length of list
pain_list_all_neurons = [0, 0, 0, 1, 1]
pain_list_only_firing = [1, 1]
experience_pain(pain_list_all_neurons) # would return pain_intensity(2)
experience_pain(pain_list_only_firing) # would return pain_intensity(10)
One place where this might be incorrect is by checking if a neuron was firing, this might be seen as violating the constraint on the inactive neurons actually being inactive. But this could be conceived a third group of neurons checking for input from this set. But even if this particular program is slightly astray, it seems plausible an altered version of this would meet the criteria for proportion to matter.
Ya, this is where I’d push back. My understanding is that neurons don’t “check” if other neurons are firing, they just receive signals from other neurons. So, a neuron (or a brain, generally) really shouldn’t be able to tell whether a neuron was not firing or just didn’t exist at that moment. This text box I’m typing into can’t tell whether the keyboard doesn’t exist or just isn’t sending input signals, when I’m not typing, because (I assume) all it does is check for input.
(I think the computer does “know” if there’s a keyboard, though, but I’d guess that’s because it’s running a current through it or otherwise receiving signals from the keyboard, regardless of whether I type or not. It’s also possible to tell that something exists because a signal is received in its absence but not when it’s present, like an object blocking light or a current.)
Specifically, I don’t think this makes sense within the constraints of my thought experiment, since it requires the brain to be able to tell that a neuron exists at a given moment even if that neuron doesn’t fire:
def get_number_of_pain_neurons(nociceptive_neurons_list):
return len(nociceptive_neurons_list) # get length of list
It could be that even non-firing neurons affect other neurons in some other important ways I’m not aware of, though.
EDIT: What could make sense is that instead of this function, you have two separate constants to normalize by, one for each brain, and these constants happen to match the number of neurons in their respective brain regions (5 and 2 in your example), but this would involve further neurons that have different sensitivities to these neurons as inputs between the two brains. And now this doesn’t reflect removing neurons from the larger brain while holding all else equal, since you also replaced neurons or increased their sensitivities. So this wouldn’t reflect my thought experiment anymore, which is intended to hold all else equal.
I don’t think it’s a priori implausible that this is how brains work when new neurons are added, from one generation to the next or even within a single brain over time, i.e. neurons could adapt to more inputs by becoming less sensitive, but this is speculation on my part and I really don’t know either way. They won’t adapt immediately to the addition/removal of a neuron if it wasn’t going to fire anyway, unless neurons have effects on other neurons beyond the signals they send by firing.
This seems like a pretty good reason to reject a simple proportion account
To be clear, I also reject the simple proportion account. For that matter, I reject any simple account. If there’s one thing I’ve learned from thinking about differences in the intensity of valenced experience, it’s that brains are really, really complicated and messy. Perhaps that’s the reason I’m less moved by the type of thought experiments you’ve been offering in this thread. Thought experiments, by their nature, abstract away a lot of detail. But because the neurological mechanisms that govern valenced experience are so complex and so poorly understood, it’s hardly ever clear to me which details can be safely ignored. Fortunately, our tools for studying the brain are improving every year. I’m tentatively confident that the next couple decades will bring a fairly dramatic improvement in our neuroscientific understanding of conscious experience.
Still, I would conclude from my thought experiments that proportion can’t matter at all in a simple way (i.e. all else equal, and controlling for number of firing neurons), even as a small part of the picture, while number still plausibly could in a simple way (all else equal, and controlling for proportion of firing neurons), at least as a small part of the picture. All else equal, it seems number matters, but proportion does not. But ya, this might be close to useless to know now, since all else is so far from equal in practice. Maybe evolution “renormalizes” intensity when more neurons are added. Or something else we haven’t even imagined yet.
That anti-proportionality arguments seems tricky to me. It sounds comparable to the following example. You see a grey picture, composed of small black and white pixels. (The white pixles correspond to neuron firings in your example) The greyness depends on the proportion of white pixels. Now, what happens when you remove the black pixels? That is undefined. It could be that only white pixels are left and you now see 100% whiteness. Or the absent black pixels are still being seen as black, which means the same greyness as before. Or removing the black pixels correspond with making them transparent, and then who knows what you’ll see?
I would say my claim is that when you remove pixels, what you see in their place instead is in fact black, an absence of emitted light. There’s no functional difference at any moment between a missing pixel and a black pixel if we only distinguish them by how much light they emit, which, in this case, is none for both. I’d also expect this to be what happens with a real monitor/screen in the dark (although maybe there’s something non-black behind the pixels; we could assume the lights are transparent).
So I don’t think it’s implausible to assign split-brain patients 2x moral weight.
What if we only destroyed 1%, 50% or 99% of their corpus callosum? Would that mean increasing degrees of moral weight from ~1x to ~2x? What is it about cutting these connections that increases moral weight? Is it the increased independence?
Maybe this an inherently normative question, and there’s no fact of the matter which has “more” experience? Or we can’t answer this through empirical research? Or we’re just nowhere near doing so?
It’s plausible to assign split-brain patients 2x moral weight because it’s plausible that split-brain patients contain two independent morally relevant seats of consciousness. (To be clear, I’m just claiming this is a plausible view; I’m not prepared to give an all-things-considered defense of the view.) I take it to be an empirical question how much of the corpus callosum needs to be severed to generate such a split. Exploring the answer to this empirical question might help us think about the phenomenal unity of creatures with less centralized brains than humans, such as cephalopods.
About split brain; those studies are about cognition (having beliefs about what is being seen). Does anyone know if the same happens with affection (valenced experience)? For example: left brain sees a horrible picture, right brain sees picture of the most joyfull vacation memory. Now ask left and right brains how they feel. I imagine such experiments are already being done? My expectation is that asking the brain hemisphere who sees the picture of the vacation memory, that hemisphere will respond that the picture strangely enough gives the subject a weird, unexplainable, kind of horrible feeling instead of pure joy. As if feelings are still unified. Anyone knows about such studies?
I agree with 1. I think it weakens the force of the argument, but I’m not sure it defeats it.
2 might be a crux. I might say that unity is largely illusory and integration comes in degrees (so it’s misleading to count consciousnesses with integers) since we can imagine cutting connections between two regions of a brain one at a time (e.g. between our two hemispheres), and even if you took distinct conscious brains and integrated/unified them, we might think the unified brain would matter at least as much as the separate brains (this is Shulman’s thought experiment).
Also related: https://www.nickbostrom.com/papers/experience.pdf
There could also be hidden qualia. There may be roughly insect brains in your brain, but “you” are only connected to a small subset of their neurons (or only get feedforward connections from them). Similarly, you could imagine connecting your brain to someone else’s only partially so that their experiences remain mostly hidden to you.
Maybe a better real-world argument would be split-brain patients? Is it accurate to say there are distinct/separate consciousnesses in each hemisphere after splitting, and if that’s the case, shouldn’t we expect their full unsplit brain to have at least roughly the same moral weight as the two split brains, even though it’s more unified (regardless of any lateralization of valence)? If not, we’re suggesting that splitting the brains actually increases moral weight; this isn’t a priori implausible, but I lean against this conclusion.
On 3, at least within brains, there seems to be a link between intensity and number of responsive neurons, e.g.: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3179932/
In particular, this suggests (assuming a causal role, with more neurons that are responsive causing more intense experiences) that if we got rid of neurons in these regions and so had fewer of them (and therefore fewer of them to be responsive), we would decrease the intensities of the experiences (and valence).
Hey Michael,
Thanks for engaging so deeply with the piece. This is a super complicated subject, and I really appreciate your perspective.
I agree that hidden qualia are possible, but I’m not sure there’s much of an argument on the table suggesting they exist. When possible, I think it’s important to try to ground these philosophical debates in empirical evidence. The split-brain case is interesting precisely because there is empirical evidence for dual seats of consciousness. From the SEP entry on the unity of consciousness:
So I don’t think it’s implausible to assign split-brain patients 2x moral weight.
I also think it’s possible to find empirical evidence for differences in phenomenal unity across species. There’s some really interesting work concerning octopuses. See, for example, “The Octopus and the Unity of Consciousness”. (I might write more about this topic in a few months, so stay tuned.)
As for the paper, it seems neutral between the view that the raw number of neurons firing is correlated with valence intensity (which is the view I was disputing) and the view that the proportional number of neurons firing (relative to some brain region) is correlated with valence intensity. So I’m not sure the paper really cuts any dialectical ice. (Still a super interesting paper, though, so thanks for alerting me to it!)
One argument against proportion mattering (or at least in a straightforward way):
Suppose a brain responds to some stimuli and you record its pattern of neuron firings.
Then, suppose you could repeat exactly the same pattern of neuron firings, but before doing so, you remove all the neurons that wouldn’t have fired anyway. By doing so, you have increased the proportion of neurons that fire compared to 1.
I think 1 and 2 should result in the exact same experiences (and hence same intensity) since the difference is just some neurons that didn’t do anything or interact with the rest of the brain, even though 2 has a greater proportion of neurons firing. The claim that their presence/absence makes a difference to me seems unphysical, because they didn’t do anything in 1 where they were present. Or it’s a claim that what’s experienced in 1 depends on what could have happened instead, which also seems unphysical, since these counterfactuals shouldn’t change what actually happened. Number of firing neurons, on the other hand, only tracks actual physical events/interactions.
I had a similar discussion here, although there was pushback against my views.
This seems like a pretty good reason to reject a simple proportion account, and so it does seem like it’s really the number firing that matters in a given brain, or the same brain with neurons removed (or something like graph minors, more generally, so also allowing contractions of paths). This suggests that if one brain A can be embedded into another B, and so we can get A from B by removing neurons and/or connections from B, then B has more intense experiences than A, ignoring effects of extra neurons in B that may actually decrease intensity, like inhibition (and competition?).
I’m unclear why you think proportion couldn’t matter in this scenario.
I’ve written a pseudo program in Python below in which proportion does matter, removing neurons that don’t fire alters the experience, and the the raw number of neurons involved is incidental to the outputs (10 out of 100 gets the same result as 100 out of 1000) [assuming there is a set of neurons to be checked at all]. I don’t believe consciousness works this way in humans or other animals but I don’t think anything about this is obviously incorrect given the constraints of your thought experiment.
One place where this might be incorrect is by checking if a neuron was firing, this might be seen as violating the constraint on the inactive neurons actually being inactive. But this could be conceived a third group of neurons checking for input from this set. But even if this particular program is slightly astray, it seems plausible an altered version of this would meet the criteria for proportion to matter.
Ya, this is where I’d push back. My understanding is that neurons don’t “check” if other neurons are firing, they just receive signals from other neurons. So, a neuron (or a brain, generally) really shouldn’t be able to tell whether a neuron was not firing or just didn’t exist at that moment. This text box I’m typing into can’t tell whether the keyboard doesn’t exist or just isn’t sending input signals, when I’m not typing, because (I assume) all it does is check for input.
(I think the computer does “know” if there’s a keyboard, though, but I’d guess that’s because it’s running a current through it or otherwise receiving signals from the keyboard, regardless of whether I type or not. It’s also possible to tell that something exists because a signal is received in its absence but not when it’s present, like an object blocking light or a current.)
Specifically, I don’t think this makes sense within the constraints of my thought experiment, since it requires the brain to be able to tell that a neuron exists at a given moment even if that neuron doesn’t fire:
It could be that even non-firing neurons affect other neurons in some other important ways I’m not aware of, though.
EDIT: What could make sense is that instead of this function, you have two separate constants to normalize by, one for each brain, and these constants happen to match the number of neurons in their respective brain regions (5 and 2 in your example), but this would involve further neurons that have different sensitivities to these neurons as inputs between the two brains. And now this doesn’t reflect removing neurons from the larger brain while holding all else equal, since you also replaced neurons or increased their sensitivities. So this wouldn’t reflect my thought experiment anymore, which is intended to hold all else equal.
I don’t think it’s a priori implausible that this is how brains work when new neurons are added, from one generation to the next or even within a single brain over time, i.e. neurons could adapt to more inputs by becoming less sensitive, but this is speculation on my part and I really don’t know either way. They won’t adapt immediately to the addition/removal of a neuron if it wasn’t going to fire anyway, unless neurons have effects on other neurons beyond the signals they send by firing.
I’m also ignoring inhibitory neurons.
To be clear, I also reject the simple proportion account. For that matter, I reject any simple account. If there’s one thing I’ve learned from thinking about differences in the intensity of valenced experience, it’s that brains are really, really complicated and messy. Perhaps that’s the reason I’m less moved by the type of thought experiments you’ve been offering in this thread. Thought experiments, by their nature, abstract away a lot of detail. But because the neurological mechanisms that govern valenced experience are so complex and so poorly understood, it’s hardly ever clear to me which details can be safely ignored. Fortunately, our tools for studying the brain are improving every year. I’m tentatively confident that the next couple decades will bring a fairly dramatic improvement in our neuroscientific understanding of conscious experience.
Fair point. I agree.
Still, I would conclude from my thought experiments that proportion can’t matter at all in a simple way (i.e. all else equal, and controlling for number of firing neurons), even as a small part of the picture, while number still plausibly could in a simple way (all else equal, and controlling for proportion of firing neurons), at least as a small part of the picture. All else equal, it seems number matters, but proportion does not. But ya, this might be close to useless to know now, since all else is so far from equal in practice. Maybe evolution “renormalizes” intensity when more neurons are added. Or something else we haven’t even imagined yet.
That anti-proportionality arguments seems tricky to me. It sounds comparable to the following example. You see a grey picture, composed of small black and white pixels. (The white pixles correspond to neuron firings in your example) The greyness depends on the proportion of white pixels. Now, what happens when you remove the black pixels? That is undefined. It could be that only white pixels are left and you now see 100% whiteness. Or the absent black pixels are still being seen as black, which means the same greyness as before. Or removing the black pixels correspond with making them transparent, and then who knows what you’ll see?
I would say my claim is that when you remove pixels, what you see in their place instead is in fact black, an absence of emitted light. There’s no functional difference at any moment between a missing pixel and a black pixel if we only distinguish them by how much light they emit, which, in this case, is none for both. I’d also expect this to be what happens with a real monitor/screen in the dark (although maybe there’s something non-black behind the pixels; we could assume the lights are transparent).
All fair points.
What if we only destroyed 1%, 50% or 99% of their corpus callosum? Would that mean increasing degrees of moral weight from ~1x to ~2x? What is it about cutting these connections that increases moral weight? Is it the increased independence?
Maybe this an inherently normative question, and there’s no fact of the matter which has “more” experience? Or we can’t answer this through empirical research? Or we’re just nowhere near doing so?
It’s plausible to assign split-brain patients 2x moral weight because it’s plausible that split-brain patients contain two independent morally relevant seats of consciousness. (To be clear, I’m just claiming this is a plausible view; I’m not prepared to give an all-things-considered defense of the view.) I take it to be an empirical question how much of the corpus callosum needs to be severed to generate such a split. Exploring the answer to this empirical question might help us think about the phenomenal unity of creatures with less centralized brains than humans, such as cephalopods.
About split brain; those studies are about cognition (having beliefs about what is being seen). Does anyone know if the same happens with affection (valenced experience)? For example: left brain sees a horrible picture, right brain sees picture of the most joyfull vacation memory. Now ask left and right brains how they feel. I imagine such experiments are already being done? My expectation is that asking the brain hemisphere who sees the picture of the vacation memory, that hemisphere will respond that the picture strangely enough gives the subject a weird, unexplainable, kind of horrible feeling instead of pure joy. As if feelings are still unified. Anyone knows about such studies?