Horace Barlow obituary
The lightning flick of the tongue that secures a frog its next meal depends on a rapid response to a small black object moving through its field of view. During the 1950s the British neuroscientist Horace Barlow established that neurons in the frog’s retina were tuned to produce just such a response, not only detecting but also predicting the future position of a passing fly. This discovery raised the curtain on decades of research by Barlow and others, establishing that individual neurons of the billions that make up the visual system contribute to the efficient processing of movement, colour, position and orientation of objects in the visual world.
Barlow, who has died aged 98, combined three approaches to the question of how the brain enables us to see. He looked at how people perceive, for example measuring the smallest and faintest spot of light they could reliably detect; he studied the responses of single neurons in the retina and brain to different visual stimuli; and he developed theories to account for the relationship between what neurons are doing and the corresponding visual experience.
All his work started from the principle – apparently obvious but not often stated – that a deep, mathematical understanding of what is involved in the psychological process of seeing is an essential basis for exploring how the physiological elements of the visual system serve that end. In a vivid analogy, he wrote: “A wing would be a most mystifying structure if one did not know that birds flew.”
He is best known for demanding answers to the question of how such a complex system could work most efficiently. He was influenced by early computer scientists, and was a pioneer in seeing visual signals as information to be processed. His concept of “efficient coding” predicted that of all the information presented to the eye, the brain would transmit the minimum necessary, wasting no energy on redundant signals.
His ideas about reducing redundancy incorporated statistical approaches to probability, showing how the brain can fill in the blanks in the information it receives by estimating the likelihood of something happening in the real world. The concept of redundancy reduction, modified over time as it became apparent that some redundancy is itself useful as the brain learns, has been hugely influential.
“Instead of thinking of neural representations as transformations of stimulus energies,” wrote Barlow in a typically elegant summary after decades of work, “we should regard them as approximate estimates of the probable truths of hypotheses about the current environment.”
In parallel with his theoretical work, Barlow tested his ideas in laboratory experiments. For example, the frog is not interested in the unchanging part of its visual field, only in the fast-moving fly. Early in his career, Barlow was able to demonstrate that reduced activity in the retinal neurons surrounding the one that signalled the fly’s presence helped to pinpoint its location.
This phenomenon, known as lateral inhibition, has emerged as a common feature of the brain’s response to visual signals, and of its activity in many other settings. While neurons are not specific for particular objects in the world – there are no “bug detectors” as such – they select features such as edges and other changes in space and time, which the brain uses to rebuild the animal’s visual world in terms of its current needs and past experience.
Later in his career he worked in partnership with a series of skilled neurophysiologists, extending his understanding of the retina and visual centres of the brain one neuron at a time, and showing that individual neurons are not hardwired but can modify their responses according to the input they receive.
Born in Chesham Bois, Buckinghamshire, Horace was the youngest of six children of Sir Alan Barlow, a civil servant, and his wife, Nora (nee Darwin). Nora was the grandchild of the naturalist Charles Darwin, and had worked as an assistant to the plant geneticist William Bateson before her marriage. In an interview with Phil Husbands of Sussex University, Barlow attributed his interest in science to his mother: she “had a very scientific way of looking at things and kept asking herself and us children questions about why things were the way they were”.
From Winchester college he went on to study natural sciences at Trinity College, Cambridge. Graduating during the second world war, he obtained a Rockefeller studentship to study medicine at Harvard University in the US. He completed his medical training at University College hospital in London, before returning to Cambridge to undertake a PhD.
He remained at Cambridge as a research fellow and junior lecturer, then in 1964 he moved to the University of California at Berkeley as professor of physiological optics and physiology.
On this return to Cambridge he held a Royal Society research professorship (1973-87) and fellowship of Trinity College, and continued to collaborate, think, write and give stimulating talks until just before his death.
Barlow received many awards and distinctions, including a fellowship of the Royal Society (elected 1969) and its Royal Medal (1993), and the Society for Neuroscience’s highest honour, the Ralph W Gerard prize (2006). He enjoyed the conviviality of Cambridge high tables and was an accomplished cellist.
His 1954 marriage to Ruthala Salaman ended in divorce; they had four daughters. In 1980, he married the technology transfer consultant Miranda Weston-Smith, who survives him, along with their children Oscar, Pepita and Ida, and the children of his first marriage, Rebecca, Natasha, Naomi and Emily.
• Horace Basil Barlow, neuroscientist, born 8 December 1921; died 5 July 2020