Fleming & Michel (hereafter referred to as F&M) boldly aim to make progress on the question of what consciousness is good for. They do so by deferring to the evolutionary significance of function, a standard approach in biology. Their claim is that at some point in evolution, there was a shift from animals that lacked visual experience to animals that experienced conscious vision, and this critical event occurred when animals transitioned from aquatic to land environments. Supposedly, aquatic animals have limited sensory horizons and hence must react to visual stimuli in a time frame that is too quick for conscious visual perception. In contrast, land animals have an extended sensory horizon and are exposed to visual stimuli for longer periods of time, which enables them to use conscious vision in model-based planning.
Like many theories about the function of consciousness, the sensory horizons explanation fails to address its fundamental underlying assumption. That is, the sensory horizons hypothesis depends on visual subjective experience having causal power. Visual subjective experience must be able to causally change neural processes to generate behavioural changes (behaviour can be considered in its broadest connotation to encompass both motor acts and cognitive/mental states employed during model-based planning). Without causal power, visual experience can have no functional role as proposed by the sensory horizons hypothesis.
There is currently no known mechanism to account for how subjective experience could open ion channels to elicit the action potentials, which are needed to produce behaviour. One could propose that visual subjective experience is just neural activity of a special kind, but then why not evolve such neural activity without subjective experience? The subjective experience does not offer anything more in the way of function according to the sensory horizons hypothesis in the absence of causal power. Consequently, the sensory horizons hypothesis makes little progress on F&M’s opening introductory statement: “It’s not obvious why we are conscious.”
We could ignore the fact that, at present, we do not know how subjective experience has causal power and simply accept that, at some future time, neuroscience will reveal the answer. Given this scenario, consciousness becomes less mysterious, and indeed it is rather obvious (rather than not being obvious as F&M proclaim) that we are conscious because consciousness has special causal powers above and beyond the standard model of particle physics. This approach is the basis of folk intuitions about consciousness, i.e., we behave in the way we do because of causal drives to eat when we subjectively feel hunger or avoid noxious stimuli because of pain. However, to understand the function of consciousness, we need to dispense with these intuitions. In the case of the sensory horizons hypothesis, the question remains as to what that subjective experience of a distant stimulus provides that unconscious processing of that same stimulus does not or cannot deliver. This is the unanswered question that the sensory horizons hypothesis fails to confront.
If one persists in attributing causal power to visual experience and examines the sensory horizons hypothesis within such a framework, then there is a lot more work to be done. It seems that F&M had a particular type of terrestrial animal in mind when they developed the sensory horizons hypothesis – more like a rodent, as in Figure. 3B, which evolved ∼ 60 million years ago (Beard, Reference Beard2002) rather than ants that emerged ∼100 million years ago (Ward et al., Reference Ward2014). If they really believe it was the water-land transition that drove the evolution of conscious vision, then they must accept that ants have conscious vision and use it for conscious reasoning in model-based planning since they have excellent long-range vision across large sensory horizons (Zeil, Narendra, & Stürz, Reference Zeil, Narendra and Stürzl2014). However, insects may not possess the necessary neural architecture for subjective experience (Key, Zalucki, & Brown, Reference Key, Zalucki and Brown2021).
If we are to truly make progress on the question of what consciousness is good for, then we need to deal with the prickly issue of whether subjective experience has causal power. One approach is to propose that the function of subjective experience is not to cause behaviour but instead to represent the cause of behaviour, which is referred to as the sense-making-sense hypothesis (Key & Brown, Reference Key and Brown2024; Key & Brown, Reference Key and Brown2025). In the case of pain, pain does not cause one to remove their hand from a hot stove, but it instead provides an implicit, conscious explanation of what caused you to remove your hand. Pain also explains or represents why you will not place your hand on the stove again. In the sense-making-sense hypothesis, humans use consciousness to explain the cause of their behaviour. In a broader context, when animal brains evolved to a threshold level of cognitive complexity, they generated a need to explain why they behave in the way they do. Consciousness evolved to fulfil this function. The evolutionary advantage of such a function is that it reduces the cognitive load on the brain imposed by cognitively reasoning about the cause of behaviour, as humans so often do when subjective experience is inexplicable.
When applied to the visual system, the sense-making-sense hypothesis proposes that the visual experience of the world would implicitly explain or represent why one behaves in a particular way in that environment. Using the example of the prey-predator scenario in F&M’s Figure 3B, the visual experience of a predator on the left side of the woods explains why they chose to avoid that pathway and take the pathway to the right side. In this case, the prey uses nonconscious neural activity to perform the behaviour while the conscious visual experience of the predator represents the neural cause of that behaviour within a virtual and subjective conscious world. In the case of the aquatic environment in F&M’s Figure 3A, the fish brain lacks the cognitive complexity needed to consciously represent the cause of its avoidance behaviour and simply executes sensory processing without subjective experience.
You have
Access
Fleming & Michel (hereafter referred to as F&M) boldly aim to make progress on the question of what consciousness is good for. They do so by deferring to the evolutionary significance of function, a standard approach in biology. Their claim is that at some point in evolution, there was a shift from animals that lacked visual experience to animals that experienced conscious vision, and this critical event occurred when animals transitioned from aquatic to land environments. Supposedly, aquatic animals have limited sensory horizons and hence must react to visual stimuli in a time frame that is too quick for conscious visual perception. In contrast, land animals have an extended sensory horizon and are exposed to visual stimuli for longer periods of time, which enables them to use conscious vision in model-based planning.
Like many theories about the function of consciousness, the sensory horizons explanation fails to address its fundamental underlying assumption. That is, the sensory horizons hypothesis depends on visual subjective experience having causal power. Visual subjective experience must be able to causally change neural processes to generate behavioural changes (behaviour can be considered in its broadest connotation to encompass both motor acts and cognitive/mental states employed during model-based planning). Without causal power, visual experience can have no functional role as proposed by the sensory horizons hypothesis.
There is currently no known mechanism to account for how subjective experience could open ion channels to elicit the action potentials, which are needed to produce behaviour. One could propose that visual subjective experience is just neural activity of a special kind, but then why not evolve such neural activity without subjective experience? The subjective experience does not offer anything more in the way of function according to the sensory horizons hypothesis in the absence of causal power. Consequently, the sensory horizons hypothesis makes little progress on F&M’s opening introductory statement: “It’s not obvious why we are conscious.”
We could ignore the fact that, at present, we do not know how subjective experience has causal power and simply accept that, at some future time, neuroscience will reveal the answer. Given this scenario, consciousness becomes less mysterious, and indeed it is rather obvious (rather than not being obvious as F&M proclaim) that we are conscious because consciousness has special causal powers above and beyond the standard model of particle physics. This approach is the basis of folk intuitions about consciousness, i.e., we behave in the way we do because of causal drives to eat when we subjectively feel hunger or avoid noxious stimuli because of pain. However, to understand the function of consciousness, we need to dispense with these intuitions. In the case of the sensory horizons hypothesis, the question remains as to what that subjective experience of a distant stimulus provides that unconscious processing of that same stimulus does not or cannot deliver. This is the unanswered question that the sensory horizons hypothesis fails to confront.
If one persists in attributing causal power to visual experience and examines the sensory horizons hypothesis within such a framework, then there is a lot more work to be done. It seems that F&M had a particular type of terrestrial animal in mind when they developed the sensory horizons hypothesis – more like a rodent, as in Figure. 3B, which evolved ∼ 60 million years ago (Beard, Reference Beard2002) rather than ants that emerged ∼100 million years ago (Ward et al., Reference Ward2014). If they really believe it was the water-land transition that drove the evolution of conscious vision, then they must accept that ants have conscious vision and use it for conscious reasoning in model-based planning since they have excellent long-range vision across large sensory horizons (Zeil, Narendra, & Stürz, Reference Zeil, Narendra and Stürzl2014). However, insects may not possess the necessary neural architecture for subjective experience (Key, Zalucki, & Brown, Reference Key, Zalucki and Brown2021).
If we are to truly make progress on the question of what consciousness is good for, then we need to deal with the prickly issue of whether subjective experience has causal power. One approach is to propose that the function of subjective experience is not to cause behaviour but instead to represent the cause of behaviour, which is referred to as the sense-making-sense hypothesis (Key & Brown, Reference Key and Brown2024; Key & Brown, Reference Key and Brown2025). In the case of pain, pain does not cause one to remove their hand from a hot stove, but it instead provides an implicit, conscious explanation of what caused you to remove your hand. Pain also explains or represents why you will not place your hand on the stove again. In the sense-making-sense hypothesis, humans use consciousness to explain the cause of their behaviour. In a broader context, when animal brains evolved to a threshold level of cognitive complexity, they generated a need to explain why they behave in the way they do. Consciousness evolved to fulfil this function. The evolutionary advantage of such a function is that it reduces the cognitive load on the brain imposed by cognitively reasoning about the cause of behaviour, as humans so often do when subjective experience is inexplicable.
When applied to the visual system, the sense-making-sense hypothesis proposes that the visual experience of the world would implicitly explain or represent why one behaves in a particular way in that environment. Using the example of the prey-predator scenario in F&M’s Figure 3B, the visual experience of a predator on the left side of the woods explains why they chose to avoid that pathway and take the pathway to the right side. In this case, the prey uses nonconscious neural activity to perform the behaviour while the conscious visual experience of the predator represents the neural cause of that behaviour within a virtual and subjective conscious world. In the case of the aquatic environment in F&M’s Figure 3A, the fish brain lacks the cognitive complexity needed to consciously represent the cause of its avoidance behaviour and simply executes sensory processing without subjective experience.
Acknowledgements
None.
Financial support
This work was supported by an Australian Research Council Discovery Grant DP200102909.
Competing interests
None.