The lights and shadows of consciousness

As George Eliot observed, it is a watershed moment when we realise that other people have “an equivalent centre of self, whence the lights and shadows must always fall with a certain difference”1Eliot G. Middlemarch. Penguin, London2003Google Scholar. In a sense, these other “centres of self” will always elude us. Other people may tell us what they are feeling, and we may try to empathise, but we can never fully project our own perspective into theirs, or theirs into ours. Then again, Eliot did not have a VR headset. In a memorable passage in Being You, neuroscientist Anil Seth describes experiencing a ‘virtual body swap’. You stand next to a partner, both of you wearing headsets displaying a live video feed and both wearing eye-level cameras with the feeds swapped. You appear in your own visual field. You walk up to yourself and shake hands. You start to feel as though the visually distant hand is their hand and the visually closest hand is your hand. In one variant, you look at your new body in the mirror, then give your old body a hug. This ingenious setup represents the promise, and perhaps also the pitfalls, of contemporary consciousness science. Being You is an engaging and accessible tour through the field’s boldest theories, most creative experiments and most surprising findings. You could give the book to a smart teenager and get them asking questions that they will be thinking about for the rest of their lives. It excites, inspires and seems certain to draw new people into consciousness science. Part of what makes Being You such a good entry point is the lack of dogmatic tub-thumping for any particular theory. Consciousness science contains dizzying disagreements about the correct theory: the spectrum ranges from views in which consciousness is an illusion to views in which it pervades the universe, with many varieties of intermediate position. All such theories have speculative elements, and current evidence does not decide between them. Being You is honest about this unfortunate situation but makes a convincing case that we don’t need consensus on a grand theory to begin stitching together a patchwork of relevant evidence. To do this, Seth advocates a strategy he calls tackling ‘the real problem’. This term is a retort to fellow VR enthusiast David Chalmers, who in the 1990s distinguished ‘easy problems’ of consciousness from the ‘hard problem’. The ‘easy problems’ are those of explaining the various functional capacities related to consciousness, such as our capacities to report what we are seeing, draw on sensory information in planning and reasoning, exert top-down control over our actions, and so on (it’s a long list). The ‘hard problem’ is explaining why any of this information processing leads to conscious experiences. As Chalmers puts it, “why doesn’t all this information-processing go on ‘in the dark’, free of any inner feel? […] Why should physical processing give rise to a rich inner life at all?”2Chalmers D.J. Facing up to the problem of consciousness.J. Consciousness Stud. 1995; 2: 200-219Google Scholar. Our difficulty in getting any grip on the hard problem is why such wildly different theories proliferate. For Seth, there is a valuable research programme that targets neither the hard problem (directly) nor the easy problems. His insight is instead to ask, what levers of control can we find, both inside and outside the brain, that allow us to manipulate the content and character of a person’s subjective experience? Hallucinogenic drugs are an obvious example, but they are rather crude levers of control. Can we find more precise, targeted ways of producing similar effects? This would give us the means to predict and explain (in a causal sense of the word) why our subjective experiences have their particular content and character (or ‘phenomenology’). The ‘virtual body swap’, originally developed by Henrik Ehrsson3Ehrsson H.H. The experimental induction of out-of-body experiences.Science. 2007; 317: 1048Crossref PubMed Scopus (648) Google Scholar, is one example of the ‘real problem’ programme. It allows us to look for levers of control over a specific kind of experience, namely the experience of bodily ownership. The evidence points to the importance of visually confirming predictions generated by motor control systems (also known as ‘efference copy’ or ‘corollary discharge’). When the two subjects shake hands, the closest hand appears exactly where your hand is predicted to be right now, according to the internal models that control your movement and register proprioceptive feedback. This combination of concordant visual information, proprioceptive signals and motor prediction generates a feeling that the visually closest hand is yours. Another example is the ‘hallucination machine’ developed by Seth’s group at the University of Sussex4Suzuki K. Roseboom W. Schwartzman D.J. Seth A.K. A deep-dream virtual reality platform for studying altered perceptual phenomenology.Sci. Rep. 2017; 715982Crossref Scopus (43) Google Scholar. This VR experience uses a machine-learning algorithm to impose top-down predictions on a visual scene. You set it to look for faces of dogs in the university’s central plaza, put on the headset and are immersed in a scene where dog faces leap out from shadows, corners, people’s backs — any pattern of sensory stimulation that includes the tiniest hint of a dog-like shape. This provides a model for what some hallucinogens do to early visual processing, indirectly telling us something about normal vision. This normal vision, Seth argues, is a ‘controlled hallucination’ in which top-down predictions are kept in check by bottom-up error signals, corrected just the right amount to help us navigate the world efficiently. What we ordinarily call ‘hallucination’ is the result of knocking that process out of balance, so the top-down predictions carry too much weight and the error signals too little. Current Biology readers will be wondering what this ‘real problem’ programme can tell us about other animals. The answer that Being You suggests is: frustratingly little. After all, we cannot have a virtual body swap with a bat. No VR headset or hallucination machine can reveal what it is like to echolocate5Nagel T. What is it like to be a bat?.Philos. Rev. 1974; 83: 435-450Crossref Google Scholar. High-tech methods tend to be human-only, reliant on equipment calibrated to human senses, and on exceptionally well-behaved laboratory subjects who follow instructions. And there is a more general problem: many methods in human consciousness science remain heavily dependent on humans’ special ability to report their experiences and understand each other’s reports. Moreover, these methods usually seek levers of control over experiences, taking for granted that the subject is conscious. But what happens when we turn from fellow mammals (such as bats) to more evolutionarily distant candidates for consciousness (such as octopuses)? It is natural to wonder not only what an octopus’s experiences are like (what is it like to have eight arms partially autonomous of the central brain?) but also whether there are any experiences there at all. Could some invertebrates be navigating the world without any conscious experiences? We may eventually face a similar state of uncertainty in relation to AI and robots. Seth’s ‘real problem’ programme says little about how to tackle these questions. At face value, they seem to be precisely the sort of questions that call for grand theories — those grand theories that no one can agree on. Seth dedicates the last two chapters of the book to animals and AI, respectively, highlighting recent work in these areas (including our own) but also acknowledging the need for humility and caution. As we look to ever more distant taxa, “the evidence becomes sparser and sketchier, and inferences about consciousness more tentative […] At some point, it becomes difficult to say anything substantive” (p. 243). To further complicate matters, intelligence and consciousness may decouple in both animals and future AI systems. For all we currently know, very high levels of intelligence may be achievable without any ‘inner feel’ whatsoever, whereas animals with very limited intelligence may nonetheless be conscious. Sensibly, Seth cautions against using intelligence as a proxy for consciousness. It’s not clear though that he always heeds his own advice. To argue for consciousness in octopuses, Seth lists flexible problem-solving, completing complex mazes and learning from others: signs of intelligence. At times, Seth also gives too much credibility to anecdotal evidence. Watching macaques leaping into a pond convinced him that the monkeys were having fun. After an octopus escaped its tank, he believed the crafty mollusc had deliberately lulled him into a false sense of security, showing theory of mind. A science of animal consciousness must move beyond such anecdotes and embrace the sort of careful experimental work that Seth champions in the human case. Over the long term, we need to develop ways of disentangling conscious and unconscious processing that go beyond verbal report and crude proxies, such as intelligence or brain size. Measuring consciousness with verbal report is, we hope, akin to measuring a liquid’s temperature by putting your hand in it: an initial measurement technique that we will ultimately transcend. To make progress on this problem, our own recent work has proposed specific cognitive markers of conscious processing, such as certain types of learning that are linked to consciousness in humans6Birch J. Ginsburg S. Jablonka E. Unlimited associative learning and the origin of consciousness: A primer and some predictions.Biol. Philos. 2020; 35: 56Crossref PubMed Scopus (40) Google Scholar, 7Birch J. The search for invertebrate consciousness.Noûs. 2022; 56: 133-153Crossref PubMed Scopus (41) Google Scholar, 8Crump A. Birch J. Animal consciousness: The interplay of neural and behavioural evidence.J. Consciousness Stud. 2022; 29: 104-128Crossref Scopus (5) Google Scholar. This approach adds a layer of subtlety to the relationship between intelligence and consciousness, given that these ‘cognitive markers’ require a certain level of intelligence to achieve. In this picture, intelligence provides a window into consciousness by creating new ways for an animal to convince us that it is conscious. They are not the same thing, but they are not unrelated either. It is no coincidence that the invertebrates usually considered the strongest candidates for consciousness (octopuses) are also among the most intelligent. The science of animal consciousness is at an early stage of development. How should we treat animals in the short term, while we wait for better methods and stronger evidence? Seth rightly emphasises the special ethical significance of behavioural signs of pain and suffering, such as directed wound-tending behaviour. When animals display such signs, as octopuses do, there is an ethical imperative to assume that they can suffer and treat them accordingly9Birch J. Burn C. Schnell A. Browning H. Crump A. Review of the Evidence of Sentience in Cephalopod Molluscs and Decapod Crustaceans. LSE Consulting, London2021Google Scholar. In turn, this means taking proportionate steps to protect their welfare, regardless of continuing debate about the nature of consciousness.