I’ll talk about the methods that scientists have used to attempt to study consciousness in animals. For perhaps the first time in the history of this blog, I’ll write about science without making any specific reference to cephalopods – I’m saving that for part 3. Here I’ll just cover enough background get a basic handle on the study of consciousness in non-humans, so that I can talk all about its application to cephalopods next time.
I’ll refer primarily to three review articles as I move through the various paradigms used to argue for or against non-human consciousness. These articles are Animal consciousness: a synthetic approach by Edelman and Seth (2009), Subjective experience is probably not limited to humans: The evidence from neurobiology and behavior by Baars (2005), and Affective consciousness: Core emotional feelings in animals and humans by Panksepp (2005). There are many good articles and books on the topic that I am not covering here, so feel free to point out what might be better/useful sources in the comments if you think I’ve missed something important.
In any case, let’s dive right in!
We have to start out assuming that the question of consciousness in non-human animals is worth investigating Where do we start?
The first thing to do is to operationalize consciousness. We have to determine how we will identify consciousness in non-human animals, if it exists. The classic way of studying consciousness in humans is through “accurate report”, which Edelman and Seth (2009) define as “a first-person account of what an individual is experiencing, made without the attempt to mislead.” Assuming that you believe that other humans are actually conscious (which can be argued; I won’t get into that here, though,) this is as direct a way as any to study consciousness. It is, however, very difficult to do with animals, as we for the most part lack any reliable form of verbal communication with non-humans. Notable possible exceptions to this include parrots (like Alex the Grey Parrot, who learned language well enough to pretty unambiguously demonstrate cognitive capacities such as numerical representation and the ability to categorize objects) and some chimpanzees who have been taught to use simple language (for example, Washoe, who was taught to use American Sign Language to communicate with her keepers.) Despite these exceptions, linguistic reports remain a rare and difficult-to-use tool for studying consciousness in animals.
One way of working around the inability of most animals to use language (and our inability to interpret the other ways they might be projecting information) is to allow the animals to report on their experience through some sort of trained response, such as by pressing a lever, pushing a button, or another physical activity. For example, Baars (2005) describes a study (Cowey and Stoerig, 1995) in which Macaques were trained to touch a screen where a target stimulus appeared, and then also to indicate (by pressing a button) whether they had perceived any stimulus on the screen (known as a “signal-detection task”, this is a pretty standard way to determine whether an intact animal can sense something.) After damaging parts of the cortex that process visual information in these monkeys, the experimenters found that they continued to point to the correct spot, but they not longer reported seeing a stimulus when the stimulus was in a certain part of the visual field. This parallels a phenomenon known as “blindsight” in humans, where a subject will claim not to perceive anything in a part of the visual field but will otherwise show basically normal behavioral responses to objects in that portion of the visual field. By training the monkeys in this study to report on their experience, the authors of this study were able to show that their awareness of their sensory world is separable from the at least some of the basic functionality of their sensory world, arguing that they have some sort of conscious perception of the world on top of the ability to make motor responses to sensory stimuli. By providing a way for animals to make “commentary” on their experience, Baars claims, methods like this provide a method of studying consciousness that is functionally equivalent to the method of accurate report in humans.
In some cases, animals do not need to be trained to show behavioral evidence of complex cognitive processes, which suggest (but importantly do not prove) the existence of consciousness. For example, as part of their arguments for the possibility of consciousness in birds, Edelman and Seth (2009) cite observations of birds exhibiting object constancy (which is the ability to attend to an object even though it leaves the visual field, such as when it is hidden behind another object – for example, peek-a-boo is fun because young babies do not have object constancy, and so they act as if you disappear when you are hidden from sight,) using and modifying tools, and changing their behavior based on their perceptions of being watched by other birds. They argue that these behaviors show that birds have a working memory and spatial cognition as well as “the ability to make sophisticated discriminations and to plan behaviors before executing them.”
Other behavioral experiments get at the question of whether animals have “selfhood” – that is, do animals have a sense of identity? Such a distinction between self and other is considered key to the sort of “higher-order” consciousness that humans have. The most classical method of doing this in humans and apes is by testing to see if they can recognize themselves in a mirror. This ability is rather straightforwardly called Mirror Self-Recognition (or MSR.) It has been used on many animals, and some that appear to have the ability to recognize themselves include dolphins, chimpanzees, gorillas, and (in one of my new personal favorite behavioral studies by Plotnik et al., 2006) elephants.
If you’re like me, you’re a bit troubled right now. These behavioral methods fall short of actually addressing consciousness per se, and they would never fly as an argument for consciousness in animals in and of themselves (actually, the results with macaques are a veritable one-hit KO in this argument, but only because they involve a species so closely related to humans – arguments from analogy to more distant evolutionary relatives require correspondingly more evidence to make.) Behavioral experiments do not solve the problem of identifying the internal states of animals, which is what we mean when we say “consciousness.” In a particularly lucid explanation of how this problem might be solved despite the shortcomings of behavioral evidence to inform us about internal states, Panksepp (2005) argues for a “psycho-neuro-ethological triangulation” strategy to address the problem of animal consciousness. According to this strategy, we should use neurological processes (some well-studied ones are the mobilization or production of neuroactive chemicals in the body and changes in EEG patterns) as a link between the behaviors we know to be associated with conscious states in humans (in his argument, emotional states in particular) and analogous behaviors in animals. For example, we know that humans feel pain when they are burned by a hot stove (the “psycho-” component of the strategy), and they then withdrawal from the stove and attend to the site of injury. If we watch a rat touch its paw to a hot piece of metal and get burned, we can observe the same sort of reaction (the “ethological” component of the strategy.) Finally, we can attempt to identify neural processes in the rat that correspond with this behavioral reaction in the rat and in humans, as well as neural processes that correspond specifically with the perception of the event (in this case, pain) in humans. If we find that homologous neural processes and behaviors occur in both cases, we have a good case for suggesting that analogous subjective experiences also occur.
In apparent agreement with this idea, both Baars (2005) and Edelman and Seth (2009) make a case for the identification of consciousness in non-humans through the study of neural processes that resemble those associated with human consciousness. The latter authors, in their argument for the possibility of consciousness in birds, identify the presence of human-like (or conscious-like) EEG patterns in birds and the presence of a neural circuit analogous to the thalamocortical circuit of humans (which has been shown through studies of brain-damaged patients and neuroimaging studies to be closely associated with consciousness) as evidence supporting the interpretation of bird behavior as indicative of consciousness. Baars argues that the apparent evolution of these brain structures suggests that consciousness is universal at least among all mammals. Because conscious states and phenomena (for example, wakefulness, REM sleep, and sensory perceptions) are modulated by brainstem structures and “seated in” the thalamocortical circuit, structures which have not undergone much overall structure change throughout mammalian evolution, they are likely to be conserved across all mammals. This is what he claims – I regrettably do not have the expertise in paleobiology or comparative anatomy to agree with or dispute his claims about brain evolution, but they sound like they could be disputed.
In essence, the argument for consciousness in animals remains an argument by analogy from the easily acceptable existence of consciousness in humans. It uses both behavioral and neural evidence to build this case. Critically, though, it makes use of comparative neuroscience to support the existence of consciousness in non-human vertebrates. Remember, though, that non-human mammals and birds are relatively closely related to people, and so their neuroanatomy is (arguably) suitably homologous to human neuroanatomy to make such an argument. What can we make of this line of inquiry when we try to apply it to an animal that is, evolutionarily speaking, much more distantly related to humans – say, an octopus?
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