By Daniel Tarade

It's ok to eat fish because they don't have any feelings

Nirvana, Something in the Way

If an animal has eyes, can it see? Probably. Vestigial or non-existent eyes are incredibly common among cave species, with tens of thousands of examples throughout the animal kingdom.[i] If eyes no longer serve a purpose, they are rapidly lost. A corollary is that an animal in possession of eyes is most likely using them to see. A more interesting question, at least to me, is whether a seeing animal is it aware that is sees? The two abilities are not necessarily coupled. Sentient vision relates to the ability to sense and focus light to recreate an image. Conscious vision involves being able to see what you are seeing. Put simply, conscious vision is best described as your mind’s eye; a world created in your brain, an interpretation based on incoming visual cues. In humans, the cornea focuses incoming light onto the retina. When light strikes the rods and cones of the retina, an electrical signal is relayed to the brain. The information collected by the light-sensitive cells of the retina travel along two routes in the brain; the dorsal stream links visuals information with the parietal lobe that processes the location of objects in the visual field and the ventral stream that connects the temporal lobe tasked with image recognition. The result is the ability to see and identify objects in 3D dimensional space. But again, more interestingly is that you are aware of what you see.  Before I get into the case studies and basic biology, I just want to establish why I believe this exercise is worthwhile. By exploring whether an animal is aware of what it sees, we can begin to imagine whether and which animals are conscious, the implication being that these animals can not only be distressed but feel distress, not only be harmed but feel harm. In most contexts, we are limited to studying the response of animals under different conditions. It is impossible, more or less, to study what they are subjectively experiencing. However, there are humans with peculiar brain injuries that help shape the distinction between sentience and consciousness that may help us understand what goes on in the brain of other animal species and, perhaps, feel sympathy. 

First, I believe it is key to clearly establish the difference between conscious and sentient sight. Consider bacteria. It has been known for over a hundred years that certain species of bacteria exhibit phototaxis, the process of moving towards or away from light. Recently, the mechanism by which photosynthetic cyanobacteria move directionally towards light has been uncovered.[ii] Rather than sensing gradients of light, these cyanobacteria were instead observed to focus light onto the cell membrane opposite of the light source. In a literal sense, these bacteria, only three microns in diameter, are able to act as lenses. The model of positive phototaxis (i.e. movement towards light) involves the focusing of light on the opposite cell membrane, the detection of the focused light by photo receptors, the local inactivation of mobility apparatuses, and accumulation of mobility apparatuses on the membrane nearest the light source. These cyanobacteria are sentient in that they can detect light, but no one is arguing that they are conscious of what they see. It is inconceivable that the bacteria are aware of what it is seeing, much like a camera is unaware of the pictures it has taken, only the photographer. 

Now, perhaps it is appropriate to jump to humans. Bacteria are convenient because we can rule out consciousness quite easily. Humans are also convenient. In us, we can assume consciousness and communicate our subjective experiences. Two non-surprising sentences; humans can see and humans are aware of what they see. Two modifications; it is common for humans to see and slightly less common for humans to see what they see. A much-studied patient, named TN, experienced two successive strokes that damaged the occipital cortex in both lobes. Despite being ‘blind’ it was discovered that the patient still possessed the ability to navigate obstacles while walking.[iii] When instructed to walk down a hallway, the patient avoided several large and small obstacles that were placed unbeknownst to them. When interviewed, they revealed that they did not know that there were any obstacles at all and that they were simply walking normally. The strokes TN suffered damaged the ventral stream, resulting in their inability to identify objects in their visual field. However, the dorsal stream was partly intact and allowed for the sentient but non-conscious ability to see and determine the location of objects. Other examples exist in the medical literature, although the majority of other patients have regions of intact vision owing to unilateral damage to the occipital cortex. However, despite describing a blind field in their vision, upon testing, they were found to be able to differentiate objects.[iv] From the patient's perspective, they were only guessing but, in reality, they retained residual non-conscious vision. Quite poignantly, this phenomena is termed blindsight.

Personally, the phenomena of blindsight is the easiest way to wrap my brain around the idea of non-consciousness. As the cognitive dissonance lifts, other examples become obvious. Much of what we do in our lives is actually unconscious. If you are absorbed in a conversation while performing some menial task, you might find that you are actually successfully completing the job while not paying any attention. Another common phenomena is highway hypnotism, where drivers report driving long distances with no recollection of having done so.[v] However, these examples are more difficult to highlight the difference of sentience and consciousness because people slip between the two states when performing most tasks. If I ask you to picture yourself driving, it will be of yourself consciously driving. Although unnecessarily risky, I imagine those with blindsight can drive (somewhat) safely in a closed course, assuming that they have driving experience prior to their loss of conscious vision. 

Are animals conscious? This of course depends on the animal and the degree of subjective experience. A fish has eyes. A fish can orient its body such that it is facing oncoming currents, a process known as rheotaxis. Originally, this process was hypothesized to require visual cues that allow for gauging of relative motion. However, even in the absence of visual cues, fish can orient their bodies to prevent being pushed downstream. Recent work has shown that, rather than a visual process, fish can sense relative flow of either side of their body via their bilateral mechanosensory lines.[vi] This process is reflexive (i.e. sentient) and does not require consciousness, highlighted best by the application of this process to robotics. However, because some actions in a fish are reflexive does not mean that they are entirely devoid of subjective experience. Humans, after all, perform sentient but unconscious actions all of the time. Recently it was discovered that certain species of fish use tools. But, it remains to be known what, if anything, is going through the mind of fish while it is using a tool.

Perhaps the simplest subjective experience an animal can feel is pain. And yet, a debate about whether fish feel pain is still ongoing. The strongest evidence that fish experience pain focuses on behavioural changes following exposure to a noxious substance. Further, these behavioural changes can be prevented by treatment with morphine.[vii] Others dismiss this evidence. Dr. Brian Key has vocally argued that fish do not feel pain or any subjective experience. In essence, fish are not conscious. The argument is anatomical in nature, highlighting that fish lack the neurological structures associated with subjective experience in mammals and birds.[viii] With respect to the behavioural changes observed after application of a noxious substance, these actions can be reflexive. From the outsider perspective, unconscious and conscious behaviour can look identical. However, the argument is far from settled. Although fish may not have brain structures analogous to those in mammals responsible for subjective experience, it is possible that other neurological structures serve a similar function. Further, it is argued that pain, as it relates to survival and mitigating harm, is the most useful from an evolutionary perspective. Feeling pain might allow an organism to avoid harm and evade predators at a level of efficiency beyond that bestowed by mere reflexes. If fish feel anything, they probably feel pain, even if the mechanism by which they sense pain is different from humans.[ix] Interestingly enough, people on both sides of the debate have elicited anthropomorphism as a criticism of arguments they see as lacking; humans are merely projecting or withholding human qualities onto or from other species. 

Really, what I want to emphasize is how non-trivial the question of whether an animals feels pain truly is. Sentience is easier to observe. Does an organism respond to stimuli? It is sentient, and in fact we observe these phenomena in organisms as simple as bacteria. However, even in humans, incredibly complicated actions, such as walking down a cluttered hallway safely, can be unconscious Seeing a fish writhing on a fish hook does not mean it is feeling pain. Reflexive, unconscious actions are perhaps the simplest explanation. However, fish also use tools. It is more difficult to explain such behaviour as reflexive. In light of the complicated questions that still need to be resolved, researchers have proposed that a principle of charity is appropriate. As humans, we can appreciate how awful pain can be. Until we can conclusively prove that fish or some other 'lower' organism cannot feel pain, we should act as if they can. 

Post-script

This post, including my use of sentience and consciousness, is inspired by Other Minds, a wonderful book written by Peter Godfrey-Smith. With its main focus on octopi and other cephalopods, Godfrey-Smith does a wonderful job of raising interesting questions and sketching the evolution of consciousness in animals and how it might function in species that are so alien us. 

[i]  Fong, D. W., Kane, T. C., & Culver, D. C. (1995). Vestigialization and loss of nonfunctional characters. Annual Review of Ecology and Systematics, 26(1), 249-268.

[ii] Schuergers, N., Lenn, T., Kampmann, R., Meissner, M. V., Esteves, T., Temerinac-Ott, M., ... & Wilde, A. (2016). Cyanobacteria use micro-optics to sense light direction. Elife, 5, e12620.

[iii] De Gelder, B., Tamietto, M., Van Boxtel, G., Goebel, R., Sahraie, A., Van den Stock, J., ... & Pegna, A. (2008). Intact navigation skills after bilateral loss of striate cortex. Current Biology, 18(24), R1128-R1129.

[iv] Sanders, M. D., Warrington, E., Marshall, J., & Wieskrantz, L. (1974). " Blindsight": vision in a field defect. The Lancet, 303(7860), 707-708.

[v] Williams, G. W., & Shor, R. E. (1970). An historical note on highway hypnosis. Accident Analysis & Prevention, 2(3), 223-225.

[vi] Oteiza, P., Odstrcil, I., Lauder, G., Portugues, R., & Engert, F. (2017). A novel mechanism for mechanosensory-based rheotaxis in larval zebrafish. Nature, 547(7664), 445.

[vii] Sneddon, L. U. (2003). The evidence for pain in fish: the use of morphine as an analgesic. Applied Animal Behaviour Science, 83(2), 153-162.

[viii] Key, B. (2015). Fish do not feel pain and its implications for understanding phenomenal consciousness. Biology & philosophy, 30(2), 149-165.

[ix] Seth, A. K. (2016). Why fish pain cannot and should not be ruled out. Animal Sentience: An Interdisciplinary Journal on Animal Feeling, 1(3), 14.