People without a visual cortex seem to be blind yet it appears some respond to optical information from the world around them. This phenomenon is known as blindsight. The Oxford English dictionary defines it as ‘the ability to respond to visual stimuli without consciously perceiving them, a condition which can occur after certain types of brain damage.’
My understanding as a layman is that optical signals from the outside world, having been converted into neural signals by the retina, are relayed not only to the visual cortex but to other neurological centres which somehow allow the person, or animal, to take survival action – for example, avoiding crashing into a table even though they can’t touch it or consciously see the table or a picture on the wall. See this video.
In his book Nature Red in Tooth and Claw (I’ve not yet read it but hope to do so) the philosopher Michael Murray, who analysed a large amount of scientific literature, describes this phenomenon in relation to the experiencing of suffering as a consequence of injury. It seems that in humans and primates pain stimuli are transmitted to various neurological functions, one of which is related to our sense of self. When sensing pain through injury we experience self-pity, anger at our own stupidity or someone else's for letting it happen, or anger at God. We also soon think of the implications for our family and our own lives. We also anticipate pain with dread if it looks like we are at risk of injury from, say, an approaching lion. (Pain can also result from certain diseases and this is another question. I'm not sure whether the book deals with this.)
Below the level of the primates, mammals such as rabbits, deer and dogs may not, according to Murray, feel pain in a self-conscious way. Such creatures don’t have the neurological channels associated with self-conscious pain awareness present in us and other primates. What they experience is analogous to blindsight. There is a neurological reaction at a certain level. It makes a dog yelp, for instance and the animal's body senses damage in some way, causing it to behave in a way which we perceive as distress. Maybe it’s to warn other dogs to steer clear of whatever caused the injury. But there is no self-pity or anxiety about the injury and its implications. The dog is in a state it instinctively wants to escape from, and a message to avoid any situation which might lead to this state is somehow lodged deep into its neurological system (e.g. steer clear of men with guns) to govern future behaviour
Recently I learnt of reports from lobotomy patients decades ago (before the treatment became controversial) that when their prefrontal cortex was removed they often felt pain but somehow it did not bother them in any way. A clear distinction between pain and suffering.
The structure and functioning of the brain is barely understood. For instance, neurologists do not agree on the demarcation of a given zone from those surrounding it, including the prefrontal cortex. Moreover, the human prefrontal cortex, which is associated with self awareness and hence perception of suffering, is 'absolutely, obviously and tremendously different' from that of any other creature, according to J.K.Rilling , a specialist in neuroimaging. (Trends in Cognitive Science, vol.18 no.1, January 2014.)
At the lowest level of the animal kingdom – insects, worms, snails etc.–the difference is obvious to anyone. The evidence seems to indicate a single neural pathway. Possibly there is no pain at all when, say, a fly is swatted. It may take evasive action, but so would a robot programmed to move out of danger when hit by a bullet. The single neural pathway is simply to help it survive.
The idea that the natural world is cruel might be a result of arrogantly projecting the nature of our own being onto the animal kingdom in general, especially onto those animals (pets etc.) which seem closest to us. To prove this, of course, is philosophically impossible. We can only say what is the most likely situation on the evidence available and that the evidence is beginning to point in the direction of a fundamental difference between homo sapiens and any other species.
Some may worry that that this could be used to justify bad treatment of animals but I don't see it that way. We can never prove what animals feel like: as I said in a previous post certain aspects of reality cannot be reached by logic. Moreover, gratuitously harming a living being, a manifestation of life, is dehumanising and evil, regardless of whether it feels pain or suffers in a self-conscious way.
Author, 2077: Knights of Peace