at discerning patches of hollow snow, which will give way if stepped on.
Reflectance spectrophotometry has revealed that blue tits ought really to be called ultraviolet tits, since females prefer males with the most dazzlingly UV crests. All this dazzle passes us by. Human eyes can’t see it, but blue tits are not making it up. Their eyes just have different cones to ours, cones which are ‘visually sensitive to wavelengths in the near-ultraviolet.’*
* S. Hunt et. al., ‘Blue tits are ultraviolet tits’, Proc. Biol. Soc., 1998.
We cannot hear the high-end kilohertz laughter of tickled rats, nor the deep clicking of long-tusked narwhals echolocating their way through the black depths of the Arctic Ocean.
All of which goes to show only that there are biological constraints to what different animals can discover in their environments. Eagleman himself puts it very clearly when says that ‘each creature picks up on its own slice of reality.’ That is absolutely right. But it is not very melodramatic or spooky. It doesn’t have the macho tone of ‘can you handle reality as it really is?’ And so Eagleman cannot stop there, but goes on to commit himself to the disastrous doctrine that animals have no access to reality at all:
In the blind and deaf world of the tick, the signals it detects from its environment are temperature and body-odour … No one is having an experience of the objective reality that really exists.
If ‘no-one is having an experience of the objective reality that really exists’, then what is this temperature and body-odour that the tick thinks it detects? And didn’t Eagleman just now say that the world was odourless? Or did I only imagine he said that. Did you imagine it too? If we both imagined it then maybe it is an objective reality that really exists. If so, then how can the deaf-blind tick detect body-odour? To detect means ‘to discover or identify the presence or existence of.’ But in an odourless world odour has no presence or existence. You can’t detect odour in an odourless world.
Then there’s the temperature the tick thinks he feels. If feeling cold is not ‘an experience of the objective reality that really exists’, the coldness the tick thinks it detects, therefore, is a creation of itself and not out in the world. This begs the question: if icebergs, snow or permafrost are not in and of themselves cold, then how do they form?
I would like to propose a compromise. What about this? I believe the tick’s perception of coldness might happily coincide with there being some actual coldness out there. I hope you agree with me. But, I’m afraid that if we want to stay true to Eagleman, this happy compromise is, alas, quite out of the question. His stern philosophy does not, we shall see, allow even this.
‘The real world is not full of rich sensory events,’ writes Eagleman. ‘Instead our brains light up the world with their own sensuality.’
If the real world is not full of rich sensory events then why do animals suffer so badly from sensory deprivation?
In the 1960s at the University of California, Mark Rosenzweig and Michael Renner showed that if you take two rat pups from the same litter, give them the exact same diet, same light, same warmth, but raise one in a bare cage and the other in a cage with running wheel, rope walk, mud, junk rubble and – best of all – other rats, then by simply comparing the two brains in autopsy, you can tell which rat grew up in a world full of rich sensory events and which did not. The brain of the rat raised in the impoverished conditions of a bare cage will have 25 per cent fewer synapses. Its cerebral cortex will measure up to 7 per cent thinner. There will be less capillary vasculation, and less dendritic arbourisation, unlike the rich bowers of dendrites all budding with fresh synapses observable in the rat raised in enriched conditions.
A lack of complexity in physical surroundings and social interactions leads to a lack of complexity in synaptic connections. Autopsies deduce the stunted conditions of a rat’s life from the stunted brain. The proof that animals have access to the world outside their heads, therefore, is found inside their heads! The outside world, however imperfectly we perceive it, lights up our brain.
Environmental complexity has since been found critical for children between birth and six. Never again will your brain create so many new brain cells and new connections between them as it does in your first six years of life. (After that you’ve peaked). But for the brain to proliferate wildly, toddlers and young children need complex environments to play in. If not they will never fulfil the ‘exuberant synaptogenesis’ that is their birthright. Complex public spaces are especially critical if the child lives in a small, homogenous box surrounded by other small homogenous boxes. And so, in one of those weird and wonderful connections between totally different worlds, what was discovered in those Californian laboratories in the 1960s influences the design of inner city playgrounds to this very day. Thanks to those Californian experiments, the London Borough of Camden now makes sure that all its playgrounds include rope walks, rubble, mud, junk and rats.
Bishop Berkeley
Those discoveries about the effect of environmental enrichment on the brain were made at the University of California at Berkeley, a city named after the most famous proponent of the idea that the outside world cannot be known.
‘Colours, sounds, taste,’ wrote Bishop George Berkeley (1685–1753), ‘have certainly no existence without the mind.’
Bishop Berkeley was very upset by Newton’s Optics, and he responded with a series of anti-Newtonian tracts. Starting with An Essay Towards a New Theory of Vision (1709), he then broadened his attack in successive treatises and essays to include Enlightenment empiricists and materialists more generally. His philosophy, says Isaiah Berlin, is ‘rooted in a pre-Renaissance medieval spiritualism,’ * and yet it is this philosophy which makes a comeback in modern brain science books.
* Isaiah Berlin, Age of Enlightenment, 1984.
In A Treatise Concerning The Principles of Human Knowledge, Berkeley writes:
It is indeed an opinion strangely prevailing amongst men that houses, mountains, rivers … have an existence natural or real, distinct from their being perceived by an understanding.
To insist on the independent existence of houses, mountains, rivers and every last particle of matter ‘must needs be a very precarious opinion; since it is to propose without any reason at all, that God has created innumerable beings that are entirely useless, and that serve no purpose.’
Though Berkeley wrote ‘in Opposition to Sceptics and Atheists’, he infuriated his fellow Christians just as much. Boswell tells us how he sent Samuel Johnson half-barmy:
After we came out of the church, we stood talking for some time together of Bishop Berkeley’s ingenious sophistry to prove the nonexistence of matter, and that everything in the universe is merely ideal. I observed that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it – ‘I refute it thus.’*
* James Boswell, The Life of Johnson, 1791.
I love how personally Johnson takes this. When the most eloquent Englishman who ever lived kicks a rock in fury he reminds us that some propositions are best not answered in cold blood. To deny someone any claim to any kind of contact
