So controversial is Elizabeth Loftus’s research that at some of her speeches she’s had to be protected by armed guards. At other times she’s been careful not to wear her most expensive outfit, for fear that members of the audience will throw tomatoes at her.

Born Elizabeth Fishman, Loftus she is one of the world’s most influential psychologists. Her topic is memory.

Do you trust your memory? Well, according to Professor Loftus you would be unwise to do so. We are inclined to think of memory as like a video cassette, with a button which we can press and which then faithfully replays a previous episode. But it doesn’t work that way. Memory is more like a reconstruction, and one which is extremely fallible and open to manipulation.

In an early experiment — called the automobile destruction study — Loftus showed subjects films of simulated vehicle accidents. She later questioned them about what had happened, but using different language. For example, to some she asked how fast the cars were going when they hit each other; to others, how fast were they going when they smashed into each other?

The result? Those asked about the cars smashing thought they were travelling faster. A week later, many of those given the “smashed’”word “remembered” broken glass, though there was none.

This became known as the misinformation effect, and this simple experiment generated a vast industry of research. But later Loftus found something even more startling. It was not just possible to alter the memory of something which had happened. She also showed how easy it was to persuade people that something entirely false had occurred. One experiment involved asking children about the time they were lost in a shopping mall, panicky, crying, and helped by an elderly person to be reunited with their family. This scenario was entirely made-up. Yet a quarter of subjects came to believe it had actually happened.

The main significance of Loftus’s research has been for the court room. She has been a consultant or expert witness in hundreds of trials — almost every famous one you can recall including those involving Rodney King, Michael Jackson, the Menendez brothers, Oliver North, Martha Stewart and OJ Simpson.

She was prompted to experiment with implanting false memories by the spate of cases in the 1990s relating to so-called “repressed memories”, when, under the influence of therapists, children claimed they had been raped as youngsters. Loftus was suspicious. In several states, and thanks to her research, recovered memory is no longer, on its own, enough for a prosecution to proceed. But that has infuriated some therapists — hence the armed guards.

The internet mob has declared him guilty, but Loftus’s body of research might give us pause when we reflect on the allegations of sexual assault made against Woody Allen.

Born in 1944, the daughter of a doctor, Beth Fishman was raised in Los Angeles, California. The family was not deeply religious — though she took a day off school every year at Yom Kippur. A series of traumatic events blighted her childhood including, when she was 14, the drowning of her mother in a swimming pool. The body was discovered by her aunt. Years later an uncle told her that she, Elizabeth, was the one who found the body. She began to ‘remember’ more and more details of that terrible morning, quite vivid and disturbing details — until three days later the uncle admitted he’d made an error. It had been the aunt after all.

This episode only strengthened Loftus’s conviction about the unreliability of memory. That’s why she’s been willing to support so many defendants. Nonetheless, her Jewish background made one job impossible to accept. She was contacted to help in the defense of a man charged with mass murder. His name, John Demjanjuk — a Ukrainian who had moved to Ohio and was accused, by eyewitnesses, of being the concentration camp guard “Ivan the Terrible”. “The cost of testifying as a defence witness would have been too great for the people I love most”, she later wrote.

Demjanjuk, you may remember, died a free man.

David Edmonds presents the BBC World Service programme, The Big Idea, which on June 9 is about Elizabeth Loftus. [He’s also the co-author of Wittgenstein’s Poker, a book about disputed memories.]