Saturday, March 17, 2012

Weekend Post - You can't trust your eyes. Or your brain.

You can’t trust your eyes. In fact you can’t trust any of your senses. Or even your brain.

One of the most interesting areas of scientific investigation is the study of perception. I remember that as a teenager I became moderately obsessed by visual illusions and wondering how my brain could so easily be fooled.

The image here is a good example. Which of the two horizontal lines is longest? The surprising answer, even when you know it’s true, is that both horizontal lines are exactly the same length. But that’s not what your brain tells you. Your brain demonstrates quite how easily it can be fooled when it fails to correctly interpret this sort of illusion.

There are hundreds of similar examples of such illusions, some much more complicated than this one. They all exploit the sort of perceptual mechanisms that evolved over millions of years that might have been useful in the jungle or savannah where our species originated but aren’t useful any longer in the world of newspapers, smartphones and the Internet.

The great realization is that illusions like the “Müller-Lyer illusion” shown above are just the tip of the iceberg. It’s not just our vision that can be deceived, it’s our entire brain. That’s when an illusion transforms itself into that much more dangerous animal, a delusion.

One of the most common delusions we can all easily experience is called “confirmation bias”. The Skeptic’s Dictionary describes this as “a type of selective thinking whereby one tends to notice and to look for what confirms one's beliefs, and to ignore, not look for, or undervalue the relevance of what contradicts one's beliefs.” More simply, it’s the mistake of noticing and remembering things that confirm our prejudices and ignoring, or simply not seeing the things that contradict them.

I had a conversation with someone not too long ago who suggested that religious believers are more charitable than non-believers. He seemed genuinely surprised when I pointed out that perhaps the two most charitable people in the world, Bill Gates and Warren Buffett both describe themselves as agnostics. He admitted that he knew this but had “conveniently” forgotten it. I think it’s plausible that this was because these facts didn’t fit in with his worldview. Similarly, it’s easy enough for those of us who describe ourselves as atheists to forget that the vast majority of Catholic priests, for instance, are decent people and not child abusers. We remember what we find convenient to remember, not what’s inconvenient. That’s a delusion.

Another example is homeopathy. Every piece of scientific research into homeopathy has confirmed what common sense suggests. It’s nonsense and has no effect. However there are vast numbers of people who swear by it based on anecdotes like “I had a cold, took a homeopathic remedy and within about a week I was better!”

Of course they were better. That’s how colds work, they go away after about a week or 10 days all by themselves whether you take a bogus remedy or not. People forget that but remember the time that they took the useless homeopathic remedy. Believers in so-called complimentary therapies remember the times that the delusional beliefs were falsely “confirmed”.

We also make the common mistake of assuming that correlation implies causation. Because two things happen at the same time or in parallel we assume that they must be connected and one must cause the other. A good example is the observation that increases in medical knowledge in the last century have coincided with a dramatic increase in the number of deaths from cancer. Does this mean that better medicine causes cancer? Of course not, all that’s happening is that the greater lifespan brought about by better medicine has caused people to live longer and older people are much more likely to die of cancer. Cancer is an old person’s disease. Now that we’re much less likely to die from smallpox, typhoid or violence we’re dying of different things instead.

In the same way, the assumption that more and more older people are dying of cancer is somehow caused by the new presence of cellphone masts is another delusion. There is no evidence that cellphone “radiation” causes cancer. In fact the evidence suggests that it doesn’t but it’s extremely human to notice that your aged relative died shortly after the local mast was erected and that one must have caused the other. Tragically your aged relative was going to die anyway.

The good news is that simply knowing about human psychology goes a long way towards combatting these delusions. The better we understand how our brains work (and sometimes fail) the better we can avoid dangerous delusions.

No comments: