Mark Whitby, a journalist and eyewitness to the recent London Tube station police shooting, sounded convincing on CNN. He said he saw an Asian man wearing a thick coat being shot five times. Another eyewitness, Anthony Larkin, saw police chasing a 'guy who appeared to have a bomb belt and wires coming out'.
The man was, in fact, a harmless Brazilian electrician wearing a fleece, who was shot eight times. How can people so close to events, and recounting them so soon afterwards, get the essentials so wrong?
It is because people are not very good at 'replaying' events they witness. Human brains are just not made that way. Memory evolved in human beings not to serve some sort of machine-like function for the purposes of the legal system, but as a way to survive. Consequently, it is characterised by the human desire for meaning and by what psychologists call cognitive parsimony and priming. Facts are beside the point.
The desire for meaning results in a natural tendency for people to 'see' and recall an ordered version of events. It is made to fit in with the prototypes around which people organise their thinking. In this case, the model around which eyewitnesses based this experience was probably more shaped by TV dramas and news reports than actual personal experience. Hence the high-drama, suicide-bomber account of one witness and the whodunnit journalese of the other. The man was not simply chased and shot; he was 'hotly pursued, by three plainclothes officers', one of them 'wielding a black handgun ... in his left hand'.
This is not deliberate deception. Mr Larkin is probably as convinced that he saw a bomb belt and wires as the famous doctor was that he saw a monster run across a lonely Scottish road and disappear into Loch Ness. People create their memories; they are not intact records waiting to be retrieved in some sort of gigantic hard disc. They are fragmented and spread across a network of understandings about the world.
So, recalling an experience draws on an individual's whole grasp and understanding of reality. This is why people like UFO eyewitnesses are so reluctant to admit that they may have imagined their 'memory'.
Cognitive parsimony and priming refer to how the human brain has devised ways to save on resources and to pay particular attention to recent experiences. Instead of isolated bits of data, the human mind prioritises what things actually mean and how they fit into the big picture.
The past provides the mental framework; recent experience lights up certain areas. For example, it is unlikely that the first eyewitness would have thought he saw the non-existent 'heavy coat' had his mind not been primed by the suicide bomber headlines in the morning paper he was reading just before the shooting.
Eyewitness accounts are influenced by the wording of questions and the kind of responses they receive. Journalists want information, so whatever an eyewitness says is treated with veneration.
This kind of subtle affirmation plus concentrated attention from the media can put pressure on the normal process of memory creation.
These known phenomena have led to quite a bit of research into how police should handle eyewitnesses and what they report.
All these areas of remembering are controversial, but it is agreed that how, where and by whom a memory is evoked for the first and on subsequent occasions has a significant influence on the memory itself - or, to put it more accurately, on how that memory is created and recreated.
Just remember that.
Jean Nicol looks at everyday issues from the point of view of a psychologist