The hard problem: What is consciousness?
Blindsight is occasionally found in those whose blindness is caused by damage to the visual cortex of the brain, perhaps by a stroke or tumour, rather than by damage to the eyes or optic nerves. Those who have blindsight have no conscious awareness of being able to see. They are nevertheless able to point to, and even grasp, objects in their visual fields.
.. Blindsight is an example of how brain damage can abolish the conscious experience of a phenomenon (in this case vision) without abolishing the phenomenon itself. Conversely, apparently full consciousness can be retained in the absence of quite important parts of the brain. One example of this is the case of a Chinese woman born without a cerebellum. This is a structure at the back of the brain which co-ordinates movement. The woman in question thus finds it awkward to move around. But she is completely conscious and is able to describe her experiences. Unlike the visual cortex, then, the cerebellum has no apparent role in generating consciousness.
.. In 2014 Mohamad Koubeissi, an American neurologist, was trying to hunt down the origin of the epilepsy suffered by one of his patients. To do so he implanted electrodes into her brain—permissible in view of her condition’s seriousness. When he placed one near one of her claustra and switched the current on, she lost consciousness. When he switched the current off, she regained it. When he repeated the procedure several times, he got the same result on each occasion.
.. Seeking an evolutionary explanation for consciousness, they suggest that an animal which can model another’s behaviour can gain an advantage by anticipating it. They further suggest that, since the only model available to a mind that wishes to understand another’s is itself, a theory of mind necessarily requires self-awareness. In other words, consciousness.
.. Previous research had suggested that most animals, when they see themselves in a mirror, respond as to a stranger—often aggressively—and seem unable to learn, no matter how long the mirror is there, to do otherwise. Dr Gallup found that this was indeed true for two species of macaque monkey. But chimpanzees soon learned that the image in the mirror was a reflection of themselves, and even used it as a person might, to assist grooming.
.. For the sake of this thought experiment Dr Nagel assumed bats have conscious experience of the world. If they do, though, he suggested that it will be built largely on the basis of a sense—echolocation—which human beings do not possess. A human might, Dr Nagel posits, plausibly imagine some parts of a bat’s experience, such as hanging upside down for long periods, or even flying. But seeing the world through sonar is ineffable to humanity.