The following text is based on the work of Iain McGilchrist, a British psychiatrist who has spent more than 20 years studying the right and left hemispheres of the brain and their different ways of perceiving the world. His main work, „The Master and his Emissary“ is 400 pages long and I am providing a very abridged introduction here. You can find a whole lot by and about Iain McGilchrist on Youtube.

Two Hemispheres

As a neuropsychologist, I am often confronted with patients who have pronounced symptoms of a disease but no awareness of these. This phenomenon is known as anosognosia, which means non-recognition of one’s own illness, and often occurs after more extensive damage to the right hemisphere of the brain. Our brain, as you may know, consists of the deep brain structures (brainstem and midbrain), the two cerebral hemispheres, and the cerebellum, which is also divided into two. The left cerebral hemisphere is responsible for the motor and sensory functions of the right side of the body and vice versa. Apart from that, however, the two hemispheres are not symmetrical either in terms of their anatomy or in terms of their functions. For example, it has been known for more than a hundred years that the left hemisphere is the seat of speech in most people. The right hemisphere, on the other hand, was thought to have superiority in visual and spatial perceptual processes. However, in recent years it has become increasingly clear that the main difference between the hemispheres is not so much what kind of stimuli they process, but how they do it. This realization culminated in theories about two fundamentally different ways in which the two hemispheres perceive the world.

For the left hemisphere, the world consists of objects and categories that are related to each other by certain rules. The perception of the left hemisphere is focused and selective. It can only consciously perceive a small section of the world at any one time, but it does so sharply and in great detail, as if through a magnifying glass. It has a vast catalog of knowledge regarding the objects of the world and their logical relationships, which enables it to analyze and manipulate the world according to its ideas. Using tools and language are its domain. With the help of language, it simplifies the world and makes it manageable. This activity is at the forefront of our consciousness most of the day. We talk to ourselves, analyze, evaluate, formulate goals and design plans. If we can shape the world according to our ideas, we are happy. If we encounter resistance, we become angry. In studies, anger and resentment are clearly associated with the left hemisphere of the brain.

The workings of the right hemisphere are harder to describe and understand. We can say that the right hemisphere perceives the world unfiltered in its entirety. Its perception of the world is more direct, while the left hemisphere perceives the world abstracted through its knowledge. Where the left hemisphere perceives isolated objects, the right sees relationships. It keeps track of the whole and locates us in the fabric of the world. Grasping facial expressions, body language, humor, music, and social relationships are some of its domains. While left hemispheric perception is based on knowledge, and thus on what has been learned in the past, it can see the new, perceive change, and is thus crucial for creativity. It is in contact with what the left hemisphere does not know, with the unknown and unknowable, and points us to it through intuitions and pictorial insights.

What is the evolutionary meaning of the bifurcation of the brain? Why do we perceive the world in two such different and ultimately irreducible ways? The functional duality of the brain is not a purely human characteristic, but is found in exactly the same way in the animal kingdom, although the function of the left hemisphere has certainly reached its peak in humans. No other creature can abstract and manipulate the world as much as humans. But animals also manipulate their world to some degree. For example, a bird, like any other animal, must also be able to distinguish objects from the rest of the world: Seeds or worms to eat, loose twigs to build a nest. To do this, it needs focused perception to find things in the environment and a knowledge of what is edible and what is not. Both are the domain of the left hemisphere. At the same time, a bird is also prey itself, meaning that while it scans parts of the environment for relevant objects, it also needs an overview of the bigger picture and must react quickly to any potentially dangerous changes, usually movements. So it makes sense to have a perception and warning system that is completely independent of the focused search behavior, which is anchored in the right hemisphere.

The right hemisphere also warns and awakens humans when something unusual and thus potentially dangerous happens in our environment. If they suddenly hear a loud noise, the right hemisphere immediately inhibits the activity of the left and we orient the body and especially the eyes in the direction of the change in order to quickly analyze what exactly caused the change. They experience this in the extreme as a startle reaction, but it is a process that occurs every second, even in sleep. However, if they are absorbed by left hemisphere activity, this warning may not take place because now the left hemisphere is inhibiting the right to avoid distractions. And If the right hemisphere is no longer functioning properly after brain damage, these warnings may not occur at all. Anomalies in the world, in the behavior of other people, and even in oneself are no longer recognized. New things are only derived from known knowledge, but are no longer recognized in the real world. The left hemisphere is not unhappy about this, because it now lives in its own world, which is no longer questioned by the right hemisphere. Accordingly, patients with anosognosia are often unconcerned and convinced that all is well, even if they have suffered significant mental deficits or even physical paralysis. Confronted with this, the left hemisphere simply explains away the deficits with an argument that is logical in itself, but wrong in relation to reality. That this does not go well I do not have to explain further.

There are brain researchers who are convinced that our western society, which is oriented towards satisfaction through the achievement of goals and the accumulation of objects, is the product of an overvalued left hemisphere. In short, we have been so successful in our manipulation of the world that we no longer allow any other worldview to apply, and we also raise our children to function primarily left hemispherically. The problem is that the left hemisphere knows no deep sense of satisfaction and the happiness it derives from manipulating the world is always short-lived and somehow „too little“. Its solution to the existential hunger for contentment is „more and more,“ because it sees the world as a collection of objects, and more of something is usually better than less in this view. More stimulation, more consumption, more change. However, this does not provide us with real satisfaction. The existential feeling of happiness that we can experience, for example, in nature, through art or in social relationships, is based on the perception of the right hemisphere.

This is not to say that the left hemisphere is the worse of the two. Without the left hemisphere our civilization would not exist, because as apes we would never have made it to agriculture. This required something evolutionarily new: the ability to understand time, to abstract from the present moment, to plan and to shape the world according to our ideas. But we must understand that not all questions of human existence can be solved by left-hemispheric thinking. The question of happiness is one of them. What we need is – as so often – a balance. If we understand how we actually function, it can help us avoid aberrations. The left hemisphere makes us successful. But only the right side makes us complete.

K. Heß 01/2022 – translated with (free version)

Two Modes of Perception