In this segment, I continue the journey through Iain McGilchrist’s masterwork, The Matter with Things by summarising chapter three, Perception, a followup to the previous chapters, respectively titled Some Preliminaries and Attention. I strongly recommend that you listen to these in turn, but feel free to play the rebel and cut queue. No one will even notice but you, and if you don’t tell, neither shall I. Come join me.
Chapter two of The Matter with Things is titled Perception. Following the previous chapter, Attention, it’s about how we perceive what we attend to. Without attention, there is no perception, but perception is not always correspondent with the so-called reality “out there”.
From the start, McGilchrist wants to assess which hemisphere is more veridical. Spoiler Alert: It’s the right half. But you already knew that because you’ve been keeping pace. And you also know that I feel he is leaving an option on the table, that neither is veridical to the actual terrain; rather, one just better maps the map. But the question essentially resolves to the same place, not as much verity as trust.
Sensory perception occurs in both hemispheres, but it is better in the right hemisphere than the left, as the left has been somewhat relegated to re-presentation over time—the same hemisphere that is better suited for codifying and mapping using symbolic language—something reserved for the brains of primates—which gives us a virtually inexhaustible way of mapping the world.
Perception is holistic, something better handled by the right hemisphere, being as the left hemisphere is more about focus and specificity. On balance, the right hemisphere is the arbiter of performance delegation, whether to perform a task or delegate it to the left hemisphere. About three-quarters of perception functions are right hemisphere processes.
McGilchrist is partial to the position advanced by Merleau-Ponty, that is “perception as a reciprocal encounter.” Perception is not a passive act. It is an interactive intercourse with the environment. What and how we perceive is affected by our experience and the situation.
Perception involves all the available senses—and by definition none of those otherwise unavailable. He starts with vision. The right hemisphere does a lot of heavy lifting here. It handles size, shape and pattern recognition, contour, shadows, distance and depth, for example, three-dimensional space, and motion and time as well as the ability to recognise objects from unusual angles or from incomplete information, which I tend to think of as playing some Gestalt role. The right also handles colour perception, though the left maintains the colour name mapping.
The left hemisphere is slightly faster at detection, but if what is detected has any signal degradation, the right hemisphere tends to be more accurate. And since the left hemisphere is, what I’ll call lazy, it may tire quickly and space out, so the right hemisphere may have to intervene, if even a bit more slowly. Paradoxically, if the left hemisphere is given more time, its recognition error rate increases. Incidentally, one reason the right hemisphere may respond more slowly is that it is deliberating to attempt to deliver the correct response whilst the left tosses out its first best guess and declares victory. Nailed it!
Recall from the last chapter that the left hemisphere is also a master of denial, so it is unapologetic when it guesses wrong. I imagine it signalling ‘that’s not a bus’ just as it hits you and then insists that it never was a bus; that injury must have been caused by something else. Perhaps it was an untoward wrecking ball.
Without delving into details here, McGilchrist points out that much early research might be invalid because it employed cathode ray tubes—CRTs—whose mechanisms present biased information to the visual field, thereby invalidating conclusions.
An interesting area for me is that the left hemisphere is better at recognising tools—hammers and spanners—, but not musical instruments, which it perceives more as living entities. And this is an apt segue to auditory perception.
Whereas the left hemisphere is better at symbolic language processing and “the processing of meaningless noises, such as clicks”, the right hemisphere pretty much handles the rest, from pitch, inflexion, tone, phrasing, metre and complex rhythm, and melody. The left keeps tabs on basic rhythmic patterns. It is assumed that rhyming relies on both hemispheres working in concert.
For most people, music processing is a right hemisphere event, but this is not true for professional musicians, who utilise both hemispheres, likely owing to the musical language translation processing unnecessary for the casual listener.
Interestingly, the acuity of the nose is orders of magnitude superior to that of the eyes and ears. Olfactory recognition and discrimination have a right hemisphere preference, but emotional reactions to scent may be stronger in the left hemisphere.
“Apart from five very basic tastes – salt, sweet, sour, bitter and umami – which come from the tongue, all flavours come from the olfactory sense.” In general, gustatory perception is a right hemisphere function. However, there is an exception for professional wine tasters, who like professional musicians need to map experiences to words associated to rating and naming.
Remembering that the right hemisphere controls the left half of the body, whilst the left hemisphere controls the right, the sense of touch is superior in the left hand. Feelings of warmth, and temperature discriminations in general, are associated with right hemisphere activation. Interoception, the ability to perceive the internal workings of the body, is another right hemisphere process.
Local versus Global Perception
Recall that the right hemisphere captures the world holistically whilst the left hemisphere has a laser focus. This equates respectively to global and local perception. As it happens, the right can do both, but the left is limited to local. This means that if the left hemisphere is damaged, the right can pick up the slack, but if the right hemisphere is damaged, the left cannot compensate for the lost holistic perspective. In practice, the right runs the show and delegates to the left when it deems it to be appropriate for the circumstance. For some reason, normal adolescents have a bias toward local perception over global.
Pathologies of Perception
This leads us to abnormalities, such as Alzheimer’s disease. Deterioration of right hemisphere function leads to a sense of disorganisation and loss of sensation. This hemisphere is also responsible for constructing a sense of self and self-awareness. McGilchrist calls out that the term self has multiple meanings. Much of the notion of self is associated with the medial prefrontal cortex in both hemispheres, but the objectified self and the self as an expression of will (in the respect Schopenhauer spoke of) are left brain aspects.
Perception of a contiguous self over time is a right hemisphere function, the loss of which is not uncommon in cases of schizophrenia.
In discussing visual hallucinations and distortions, almost ninety per cent of these have been attributable to right hemisphere anomalies. McGilchrist shares examples over several pages, but I’ll summarise by description alone of what can be categorised under the umbrella term of metamorphopsia. These might lead to object impermanence, or viewing things as too large or too small, too close or too distant, skewed, or the wrong shape altogether. In some cases, only half of an object, including self-perception, was outsized. This might occur on a macro level or a micro level, which is to say that it may be entire objects or bodies or just faces, or just familiar faces or just eyes or just one eye. This might occur on a macro level or a micro level, which is to say that it may be entire objects or bodies or just faces, or just familiar faces or just eyes or just one eye.
Some of these cases involved motion, for example, the sense that some object is receding away from the observer as the observer draws nearer to it.
After a journey through Charles Dodgson, AKA Lewis Carroll, and Alice in Wonderland, provides a plethora of examples in prose of some of these visual effects.
From visual hallucinations, we wonder through hallucinations of the other senses, though the data points on these are much sparser, but the left hemisphere does seem to be the culprit of most auditory hallucinations.
To summarise, I am again left to feel that the left hemisphere is a deadbeat hanger-on. It’s there in a pinch, but it’s an unreliable narrator and worker that falls asleep at the wheel. Psychology does have a position on what a normal person should see and hear and taste and touch, but normal doesn’t mean real.
I was hoping to see some information and perspective on synaesthesia, a condition where people perceive experiences through sense-perception organs different to normal. These people see music and hear smells or taste colours and so on. We consider this to be anomalous, but does it provide a fitness benefit, and are these people ahead of “normal” people or are they carrying excess baggage that creates a burden, even if the condition is otherwise benign.
Now that we’ve covered attention and perception, we’ll be covering judgment in the next chapter. I hope you’ll join me.
What are your thoughts? What did you think of this chapter? Have you experienced or know of anyone who has experienced any of these so-called anomalies. Are you familiar with any of the effects mentioned in Alice in Wonderland? Leave comments below.