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Thomas Bayes and Bayesian probabilities


Science, perception and William Ockham
Richard Gregory Scientist
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I’d quite like to, you know, think a bit about, talk a bit about science itself and how science is related to perception and how we make decisions in science for our lives and how the brain makes decision which are sort of pre scientific. I mean the brain comes up with its own decisions and then it gets into science to be analysed, made explicit and then scientific method applied. All this, I think, is a hugely important issue; indeed, our survival might actually depend on doing it properly. It always has done, since primitive man, with agriculture. How do I plant this field so I’m likely to have grub next year, you know? It’s always been a probability issue. Now, I think an important character here is Ockham, William Ockham, who round about the 11th century, I can’t remember his exact date, approximately 11th century, who was a philosopher. I think he lived in Bath, actually, and he simply made the statement that you have a load of hypothesis and what you should not do is to have more assumptions for testing each hypothesis than are absolutely needed. You need the simplest possible account. You can always multiply excuses, if you like, or possible bits of new evidence or something which may be imaginary to support the hypothesis but he said, no, you should make it minimal, minimum number of hypothesis, minimum number of assumptions and then you’ve got the most powerful hypothesis. And I think he really had the idea that probabilities were involved here that the hypothesis is supported by the evidence or it can be thrown away but the thing is, it’s not black and white. You can very seldom be certain that a hypothesis is wrong or certain that it’s right. We’re pretty certain that the moon is not made of green cheese. In other words, that would be a waste of time even considering that as a scientific project, to see whether it’s made of green cheese. But where does this stop? If you want to ask is it possible to make a bomb out of uranium, 100 years ago this would have been like green cheese moon. It would have been regarded as ridiculous. Then it creeps up on you and, by golly, it isn’t only a possibility, it happens, and then you’ve got the thing, how to deal with it when you’ve got it and the probabilities keep changing. So I think that science and also the perceptual brain is always playing with probabilities and the trick is to minimise and simplify each hypothesis so that you can really say, well, this is probably right or it’s probably wrong and apply the evidence effectively, and you can only do that when it’s simple, when it’s defined. This is really from Ockham.

The late British psychologist and Emeritus Professor of Neuropsychology at the University of Bristol, Richard Gregory (1923-2010), is well known for his work on perception, the psychology of seeing and his love of puns. In 1978 he founded The Exploratory, an applied science centre in Bristol – the first of its kind in the UK. He also designed and directed the Special Senses Laboratory at Cambridge which worked on the perceptual problems of astronauts, and published many books including 'The Oxford Companion to the Mind', 'Eye and Brain' and 'Mind in Science'.

Listeners: Sally Duensing Adam Hart-Davis

Sally Duensing currently is involved in perception exhibition work and research on science and society dialogue programmes and is working with informal learning research graduate students and post-docs at King's College, London. In 2000 she held the Collier Chair, a one-year invited professorship in the Public Understanding of Science at the University of Bristol, England. Prior to this, for over 20 years she was at the Exploratorium, a highly interactive museum of science, art and perception in San Francisco where she directed a variety of exhibition projects primarily in fields of perception and cognition including a large exhibition on biological, cognitive and cultural aspects of human memory.

Born on 4 July 1943, Adam Hart-Davis is a freelance photographer, writer, and broadcaster. He has won various awards for both television and radio. Before presenting, Adam spent 5 years in publishing and 17 years at Yorkshire Television, as researcher and then producer of such series as Scientific Eye and Arthur C Clarke's World of Strange Powers. He has read several books, and written about 25. His latest books are Why does a ball bounce?, Taking the piss, Just another day, and The cosmos: a beginner's guide. He has written numerous newspaper and magazine articles. He is a keen supporter of the charities WaterAid, Practical Action, Sustrans, and the Joliba Trust. A Companion of the Institution of Lighting Engineers, an Honorary Member of the British Toilet Association, an Honorary Fellow of the Royal Photographic Society, the Royal Society of Chemistry, the Society of Dyers and Colourists, and Merton College Oxford, and patron of a dozen charitable organizations, Adam has collected thirteen honorary doctorates, The Horace Hockley Award from the Institute of Scientific and Technical Communicators, a Medal from the Royal Academy of Engineering, the Sir Henry Royce Memorial Medal from the Institute of Incorporated Engineers, and the 1999 Gerald Frewer memorial trophy of the Council of Engineering Designers. He has no car, but three cycles, which he rides slowly but with enthusiasm.

Duration: 3 minutes, 11 seconds

Date story recorded: June 2006

Date story went live: 02 June 2008