The Hemisphere Hypothesis

This post is about Iain McGilchrist’s hemisphere hypothesis. The post is written as a fictional conversation between McGilchrist and myself. I have taken McGilchrist’s answers from his two books The Master and His Emissary and The Matter with Things. I end the post with some of my own thoughts. (My emphasis in italics.)

What is the difference between what the hemispheres do?

Well, I will argue, nothing much: it is quite true that almost everything we once thought went on in one or other hemisphere alone is now known to go on in both. … The difference, I shall argue is not in the ‘what’, but in the ‘how’…

—Iain McGilchrist, The Master and His Emissary

What is the hemisphere hypothesis?

…the hemisphere hypothesis is deceptively simple: the bi-hemispheric structure of the brain makes possible attending to the world simultaneously in two otherwise incompatible ways.

Every animal, in order to survive, has to solve a conundrum: how to eat without being eaten. It has to pay precisely focussed, narrow-beam attention [‘how‘]…so as to exploit the world for food and shelter [‘what‘]. … Yet,…it must also…pay another kind of attention to the world, which is the precise opposite of the first: broad, open, sustained, vigilant attention [‘how‘], on the lookout for predators [‘what’]…

…the left hemisphere [is] being used largely for paying narrow-beam, sharply focussed attention [‘how’] to the world, for the purpose of manipulation [‘what’], and the right hemisphere for paying open, sustained, vigilant attention to the world [‘how’], in order to understand and relate to the bigger picture [’what’].

…the right half of the brain controls and responds to the left half of the body [’what’], and vice versa. That means that motor and sensory function [‘what’], as well as all manner of perception [‘how’] (except, oddly, for the sense of smell) from one half of space, both internal and external, is relayed to the opposite side of the body.

The point is that, very broadly, the right hemisphere attends to the left half of the world…, and the left hemisphere…to the right half. …how you attend to something – or don’t attend to it – matters a very great deal. …you do not see what it is you cannot see.

It is not the what, but the how, that matters…

—Iain McGilchrist, The Matter with Things

Yes, I fully agree that the ‘how’ matters a very great deal! But I’d say the ‘what‘ matters too. And, I’d suggest that the ’how’ is intimately related to the ‘what’. In short, there’s a relation between the ‘what‘ and the ‘how‘. I’d suggest we have two hemispheres because we have two body halves (two hands, two arms, two legs, two eyes, two ears, etc.) that need to be controlled and responded to.

In other words, I believe that our two hemispheres have more to do with our body plan than with attending to the world in two different ways. Why only two, by the way? There’s so much going on simultaneously in both head and body!

I think McGilchrist’s deep metaphysical assumptions might pre-structure his thinking so that they may or may not become obstacles, in a Wittgensteinian sense,¹ preventing him from seeing clearly?

Notes:
1. Wittgenstein aimed at “enabling us to see, by enabling us to look, by endlessly clearing away the obstacles that prevent such looking.” “Obstacles mostly from assumptions that pre-structure our thinking.” See Critical Notice: Iain McGilchrist, The Matter With Things: Our Brains, Our Delusions, and the Unmaking of the World by Rupert Read.

Update 2024-09-08: Link added to plast paragraph. Notes updated.