The Octopus and the Unity of Consciousness
Sidney Carls-Diamante explores whether octopus arms have their own consciousness
Posted Mar 18, 2020
This article is part of the Psychology Today animal minds series.
Recently, Sidney Carls-Diamante, a post-doctoral researcher at the Konrad Lorenz Institute for Evolution and Cognition Research, published an article, "The Octopus and the Unity of Consciousness."
In this article, Carls-Diamante uses the decentralized nervous system of octopuses as a case study to challenge the common assumption among both scientists and philosophers that consciousness must in some sense be 'unified.'
That consciousness is a unified phenomenon has been a long-standing consensus. But as Carls-Diamante points out, it is more of an unchallenged assumption, rather than an established empirical necessity. Indeed, this 'unity thesis' (Bayne 2010) of consciousness has long been taken for granted. It is the assertion that "it is possible to have only a single set of subjective experiences at any given point in time" (Carls-Diamante).
What is usually meant here is the unity of phenomenal consciousness, in the sense of how it is like to be conscious. Since Thomas Nagel's famous paper 'What it's like to be a bat?' this question has served as a heated topic of discussion not only within philosophy, but also science. In a more scientific fashion, we can ask: When are mental and physiological states accompanied by a distinctive kind of subjective experience? This raises the question of whether an octopus arm for instance could have its own distinctive kind of subjective experience, i.e. something it feels like to be an octopus arm.
"Consequently, the issue of the unity of phenomenal consciousness can be parsed as the question of the number of experiencing subjects that can be instantiated within a single organism." (Carls-Diamante)
That the unity thesis of consciousness has become so entrenched comes at no surprise. Historically, almost all philosophical and scientific work on consciousness has concerned human consciousness. Our centralized nervous system has given rise to the demand to search for the neural substrates of consciousness. Is there a specific region in the brain where consciousness arises? That the nervous system plays a crucial role in the emergence of consciousness is a fair assumption to make, for it allows science to get off the ground.
Yet, because we have primarily looked at human brains and made inferences based on similarity relationships between conscious, unconscious, and non-conscious brains, the assumption that subjective experience must be unified has become entrenched, Bayne asserting that it must necessarily be unified. He only makes this claim for humans, however:
"Some creatures simply won’t have the cognitive machinery required to integrate the contents of the mental states in the appropriate manner" (Bayne)
This is because some animals will lack the centralized brain architecture to integrate all their conscious experiences. While split-brain patients offer evidence that humans could have a disunified consciousness, experiencing the world twice (for each half of their body) Carls-Diamante argues that a particular non-human animal with a decentralized nervous system provides the best case against the unity-thesis: the octopus. As she points out:
"[. . .] what is significant and fascinating is the extensive functional autonomy of the three components of its nervous system: the central brain, the optic lobes, and the peripheral arm nervous system. [. . .] Each arm receives massive amounts of sensorimotor information from millions of receptors in the suckers, skin and muscles. The nervous centers of each arm are responsible not only for processing sensory information, but also for controlling reflexes and issuing motor commands to their respective appendages."
Indeed, the very organization of the octopuses' nervous system is so disjointed and sparsely connected to the brain as to call into doubt the very idea that they could have a unified consciousness, thus challenging the ordinary philosophical concept of 'mind' (see also Godfrey-Smith 2013 & 2016).
This, I take it, is the right approach toward a better understanding of consciousness. What is needed is a bottom-up approach that looks at the evolution of consciousness. If octopuses have evolved phenomenally conscious minds, then they have very different ones from ours. What then would such a disjointed consciousness look like, or rather feel like? This question shall be addressed in the upcoming entry.