As a student he worked with the great Frederic Bartlett and later became one of the most influential researchers in perception. He was key in demonstrating that expectations and prior experience have a ‘top down’ influence and that perceptions are often just best guesses or hypotheses about the world.
His liberal use of visual illusions demonstrated this in an instantly graspable way, making his explanations clear and immediate, and he was the first to study the perceptual effects of having lifelong cataracts removed.
Previously it was thought that perception was largely ‘all there’ during early childhood, but the fact that people who had the operation as adults couldn’t distinguish objects from each other, for example, suggested that the developing visual system learns many assumptions essential to making sense of the world.
His book Eye and Brain has probably been read by virtually every undergraduate over the last 30 years and he co-founded the Experimental Psychology Society in the UK to promote psychological science at the highest level.
There is a fantastic interview series from The Wellcome Trust where he discusses the history of perception psychology which you can watch in full on YouTube if you want to get a handle on the breadth of his knowledge.
Gregory was also a keen promoter of science education and founded The Exploratory, the first ‘hands on’ science museum in the UK, where children and adults could get their hands dirty and see scientific principles in action.
It’s also worth saying that he was a very approachable and gentlemanly character. A previous Mind Hacks post, on the fact that he was in discussion with film director Roman Polanksi to make a 3D horror movie earlier in his career was prompted by Gregory himself after I had the pleasure of chatting to him at a science event and he mentioned the curious incident.