Multiple ways to implement and infer Consciousness

What to take away

1. 1. Consciousness and sentience are never directly measured in any species, including humans — all attributions are inferred from observable behaviour such as verbal self-report or goal-directed action.
2. 2. Plants propagate action-potential-like signals along distributed vascular networks and synthesize glutamate, the most abundant excitatory neurotransmitter in the human central nervous system, providing electrochemical overlap with animal physiology despite radically different anatomy.
3. 3. Rouleau and Levin introduce a system-agnostic evaluative framework that assesses sentience-relevant response patterns without reference to the substrate producing them, intended to unify cybernetics, behavioural science, bioengineering, robotics, and biomedicine.
4. 4. The framework is grounded in two established philosophical concepts — multiple realizability (Bickle, 2006, Stanford Encyclopedia of Philosophy) and substrate independence (Bostrom, 2003, Philosophical Quarterly 53(211)) — to argue that felt states can in principle be implemented by non-neural systems.
5. 5. Biological degeneracy within nervous systems (Mason, 2015, Complexity 20, 12-21) — wherein structurally dissimilar regions such as subcortical and brainstem nuclei mediating blindsight maintain duplicate retinal maps — demonstrates that even neurons implement identical functions via disparate architectures.
6. 6. Published in Animal Sentience 33(30), DOI 10.51291/2377-7478.1817, the commentary is a direct response to Segundo-Ortin & Calvo's (2023) Animal Sentience 8(33) review, which documented that plants display classical conditioning, risk assessment, kin discrimination, and mimicry within a single lifecycle.
7. 7. Neuromorphic nanowire networks exhibiting metaplasticity (Loeffler et al., 2023, Science Advances 9(16), eadg3289) and robotic systems (Clawson and Levin, 2022, Biological Journal of the Linnean Society) are proposed as concrete non-biological substrates to which the same inferential standard for sentience should be applied.
8. 8. An open question the paper raises is whether the universe contains sentient life that achieves felt states through mechanisms entirely unlike terrestrial neural circuitry, with plant sentience characterised as likely the tip of an iceberg of consciousness yet unknown (referencing Ramstead et al., 2019, Physics of Life Reviews 31, 188-205).
9. 9. A replicable methodological choice is to operationalise sentience evaluation by listing behavioural criteria — goal-directedness, anticipation, flexibility, adaptiveness, and habituation — and applying them system-agnostically, excluding substrate identity as an admissible criterion.
10. 10. The paper predicts that a substrate-agnostic framework will prove empirically more productive than neurocentric approaches and will enable theoretical unification across at least six disciplines: cybernetics, behavioural science, bioengineering, robotics, materials science, and biomedicine.

Peer brief — for seminar discussion

Rouleau and Levin's commentary, published in Animal Sentience 33(30) (DOI 10.51291/2377-7478.1817), responds to Segundo-Ortin & Calvo's 2023 review in Animal Sentience 8(33) on plant sentience. Their entry point is an asymmetry in the epistemology of consciousness attribution: cognitive scientists routinely infer sentience in non-human animals from behavioural proxies — goal-directed action, anticipatory reorientation, risk assessment — while applying a stricter and largely unarticulated standard to plants. Rouleau and Levin argue this double standard is incoherent because consciousness is never directly measured in any substrate, humans included; all attributions are inferential. Their load-bearing contribution is the articulation of a system-agnostic evaluative framework that anchors sentience inference in observable response patterns alone, deliberately excluding the physical medium producing those patterns as an admissible criterion. The framework draws explicitly on multiple realizability (Bickle, 2006) and substrate independence (Bostrom, 2003, Philosophical Quarterly 53(211)), and is supported empirically by biological degeneracy within nervous systems (Mason, 2015, Complexity 20, 12-21), including blindsight mediated by subcortical nuclei maintaining independent duplicate retinal maps, and by the fact that plants already synthesize glutamate — the dominant excitatory neurotransmitter in the human CNS — and propagate action-potential-like signals along distributed vascular networks. Extension of the framework reaches beyond biology to nanowire networks exhibiting neuromorphic metaplasticity (Loeffler et al., 2023, Science Advances 9(16), eadg3289) and robotic systems (Clawson & Levin, 2022). The implicit prediction is that substrate-agnostic criteria will unify cybernetics, bioengineering, materials science, and biomedicine more productively than substrate-specific theories. An alternative method the framework could have been stress-tested against is integrated information theory (IIT), which assigns a quantitative consciousness measure (Φ) to systems irrespective of biological substrate and would constitute a competing system-agnostic approach. A critical reader would push back most forcefully on the framework's conflation of functional equivalence with phenomenal equivalence: showing that plants, nanowire networks, or robotic systems produce behaviourally analogous outputs — habituation, kin discrimination, classical conditioning — does not establish that the same inferential leap warranted for animals (whose phylogenetic proximity to humans grounds analogy arguments) is equally warranted for radically dissimilar systems. The argument from multiple realizability establishes that sentience could be substrate-independent in principle, but it does not establish that any particular non-neural system actually instantiates it; the framework risks collapsing the distinction between functional and phenomenal consciousness, a gap the commentary does not close.

Claims (7)

• A system-agnostic approach offers the best roadmap for a deep, empirically fruitful unification of frameworks across cybernetics, behavioural science, bioengineering, robotics, materials science, and biomedicine.

  Prescriptive claim that ignoring substrate will unify diverse fields.

• If different organizations of nervous tissue can achieve the same functions, the possibility that cognitive capacities, including sentience, can be achieved by other tissues should be considered.

  Conditional claim urging consideration of non-neural tissues for cognition.

• A system-agnostic approach evaluating observable response patterns without reference to substrate offers the best roadmap for empirically fruitful unification.

  Core argumentative position: sentience assessment should focus on behavior, not substrate composition; extends to AI and robotic systems.

• It is highly implausible that all sentient life in the universe achieves felt states using the neural circuitry underlying human Consciousness on earth.

  Reinforcement of substrate independence: Earth-like neural circuits are unlikely to be the sole substrate.

• All attributions of cognition, including sentience, are always inferred on the basis of embodied behaviours, including verbal self-report in humans.

  Stronger version: all cognition attributions rely on observable behavior.

• Cognitive functions, including sentience, can potentially be achieved by very different systems and their disparate substrates.

  Central multiple-realizability claim of the paper, from abstract and §2.

• Cognitive functions such as sentience are always inferred.

  First sentence of the paper, establishing the inferential nature of all sentience attributions.

Hypotheses (1)

• Felt states can be achieved in multiple ways and by many different biological substrates, analogous to how computation is multiply realizable.

  Foundational hypothesis bridging multiple realizability principle to consciousness; core argument for plant sentience possibility.

Questions (1)

• If felt states in humans and other animals are always inferred, why is the same leap from observable behaviour to inferred sentience not afforded to other organisms, including plants?

  Central question of the commentary; challenges the double standard in attributing sentience.

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