Why We Are Not Zombies

Human consciousness has been called the last unexplored continent. We all have experiences, thoughts and feelings. From an early age, we also develop self-awareness, which is the ability to reflect on our thoughts and feelings. These are everyday phenomena, but three big questions arise: How does consciousness arise? What does it consist of? What is the point of having a consciousness? A new book by British psychologist Nicholas Humphrey, titled Sentience: The Invention of Consciousness, attempts to answer these questions.

Regarding the first question, everyone seems to agree that the brain is required. In recent decades, research has provided us with some knowledge about which parts of the brain are involved in different consciousness processes and how damage can lead to limitations in function. For example, damage to the visual cortex can lead to 'blindsight'. This means that the patient experiences themselves to be blind, but because other pathways for visual information are still functioning, the patient can avoid obstacles and even duck if something is thrown at them. As a young researcher in the 1960s, Humphrey studied a rhesus monkey that had its visual cortex removed. However, the monkey could be trained to do more and more things as if it could still see. This later led his boss, neurologist Larry Weiskrantz, to identify blindsight in human patients. These patients have normal consciousness experiences in the other senses, but their visual experiences are gone. It is conceivable that an individual could lose the experiences of the other senses as well but still act appropriately in many situations. Such an individual would be close to what is called a zombie, that is, someone who acts in a human-like way but lacks consciousness. Although such patients have not been detected, they would have a very limited repertoire of actions.

Regarding the question of what consciousness consists of, the first thing to note is that sensory impressions are combined with emotional components to form a unit. T. S. Eliot writes that consciousness is like "music heard so deeply that it is not heard at all, but you are the music while the music lasts". The senses and the emotions can be seen as the different instruments in an orchestra that together form a coherent sound. Some people may lack one of the instruments, but the music can still be melodious. Other animal species have other instruments that make their music different from ours: dolphins and bats have echo-navigation and some birds can sense the Earth's magnetic field. So, one way to answer the question of what consciousness consists of is to say that is it like music, a chord of tones.

Humphrey distinguishes between sensations and perceptions. A sensation is what is given by the sensory receptors – an uninterpreted impression, while a perception is what is filled in by different mechanisms in the brain – an interpreted impression. What we perceive is usually not sensation, but rather what we expect from the patterns we have learned. Sensory mechanisms therefore play a double role. When I hear the song of a blackbird, the sensation answers the question "What is happening to me?" while the perception answers the question "What is happening in the world?"

Sensations are linked to a particular sensory domain: such as vision and hearing, while perceptions are a combination of various sensory impressions. The reason for this is likely that perceptions, as they are about what is in the world, are more useful if they are available to all thought processes and are not limited to any particular sense.

The brain also fills in the minds of others – we perceive their feelings, thoughts, and desires. This is known as mentalizing or mind-reading. The capacity is particularly noticeable in a conversation where we often anticipate what the other person will say. The capacity is necessary for us to cooperate effectively with each other.

According to Humphrey, our ability to reflect on our own thoughts, feelings and decisions, known as self-consciousness, is a prerequisite for mentalizing with others. However, others, like philosopher of religion Martin Buber, reverse the order and argue that you-consciousness precedes self-consciousness. Child psychologists Colwyn Trevarthen and Stein Bråten support this perspective, stating that newborns cannot separate the experience of itself from the experience of their mother until a sense of self emerges later on.

Many of the processes that create consciousness can be described as simulations that generate new phenomena. In particular, our perceptions of light and sound extend in time, even though these stimuli are instantaneous. For example, when we hear a melody, we perceive the pattern of the melody because previous notes remain in our minds for a while. Such an extension allows us to perceive music.

Already in his earlier book, A History of the Mind, Humphrey theorizes that consciousness is a form of simulation that creates internal loops. For instance, when we hear a lion’s roar, we need to keep the idea of the lion in our minds for a while to prepare. By looping the perception of the lion in our mind, we can achieve this. In his latest book, Humphrey expands on the theory, although gaps in the explanation of how the simulations evolved remain.

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The third question of what is the point of having consciousness requires an evolutionary explanation. Humphrey argues, somewhat controversially, that there cannot be creatures with a partial consciousness, and thus, there must be a clear boundary in the course of evolution when consciousness emerges. He speculates that warm-bloodedness is required for consciousness. One reason he gives is that nerve impulses become faster as their body temperature increases. Cold-blooded animals become passive when their body temperature drop, but warm-blooded animals can evolve larger brains due to their greater efficiency.

Mammals and birds are warm-blooded and Humphrey believes that only these groups of animals are conscious. He argues that they are the animals who actively seek out positive experiences, which he calls “qualiaphilia” after the concept of qualia, which in philosophy refers to subjective experiences.

A recently published example of animals seeking pleasurable experiences comes from psychologist Adriano Lameira and linguist Marcus Perlman, who studied films of chimpanzees, gorillas and orangutans spinning on ropes. They conclude that the apes do this to achieve an "altered mental state". This expression is too ambitious. Children like to roll down hillsides just for the sensation of being dizzy. Therefore it is likely that the spinning behavior in apes is not a sign of a more sophisticated consciousness, but rather a desire to experience pleasure.

As evidence for qualiaphilia in mammals and birds, Humphrey cites their playfulness, which is something done for fun. But he may be wrong here: play has also been observed in several other animal groups, such as turtles, crocodiles and octopuses, which are not warm-blooded. For example, if an alligator is given a choice between food or a new toy, it often chooses the toy, which is a clear sign of qualiaphilia.