Mammalian evolution was dominated by the engineering of vision – not through radical changes in the design of the eye, but through the gradual discovery by the brain of new ways of interpreting the retinal image to gain ever more comprehensive knowledge of the nature of the world. Surely human vision is the pinnacle of this process. Visual experience is like a finely detailed, seamless movie, generated by neural machinery that occupies one third or more of our cerebral hemispheres, decoding the 150 megabytes per second of information that gushes in from the optic nerves. But growing evidence is revealing that vision is largely ‘sleight-of-brain’ – an extraordinary conjuring trick that creates the reassuring sense of reality out of almost nothing. Most of what we do with the information from our eyes – controlling our hands, guiding our posture, deciding what to look at – happens without awareness. We are also usually unaware that our eyes jump from place to place three times a second, yet these sudden shifts of the retinal image must totally disrupt the processing of information in the brain. Although vision seems continuous and stable, it is actually a series of snapshots, each one lost as the eyes move on. And during each snapshot, the brain gathers and stores only the few features that we can attend to at any one time. In turn, this drop of knowledge, distilled from the flood of information, enters short-term memory and contributes to what we really know and remember of our visual world. One deep question arises: if we are genuinely aware of such a small fraction of what we see, why do need to be conscious of anything?

Colin Blakemore is Professor of Neuroscience at the University of Oxford and a Fellow of Magdalen College. He also holds a Professorship at Warwick and is Chairman of the Neuroscience Research Partnership in Singapore. Colin studied Medical Sciences at Cambridge and completed a PhD at the University of California, Berkeley. After working for 11 years in Cambridge, he moved to Oxford as Waynflete Professor of Physiology in 1979. From 2003–2007 he was Chief Executive of the UK Medical Research Council. His research has been concerned with many aspects of vision, early development of the brain and plasticity of the cerebral cortex. He has been President of the British Neuroscience Association, the Physiological Society and the Biosciences Federation. He is also passionately committed to public communication and engagement, for which he has won many prizes, including the Royal Society Michael Faraday Prize. He has been President and Chairman of the British Association for the Advancement of Science. He gave the Royal Institution Christmas Lectures in 1982 and this is his third Discourse.