Memory is a major contributor to clinical decision-making. Doctors rely on the good memory of their patients or eyewitnesses when they take a history, and they also depend on their own memory when remembering appropriate differential diagnoses, investigations, and treatments. Memory however has several significant flaws that hark back to the process by which it is formed, and the mechanisms by which it is recalled.
In demonstrating how memory works, it is perhaps most helpful to discuss how it doesn’t work. For example, memory is not like a wax tablet in which events are etched exactly as they occurred, nor is it like a video recording that captures and replays the minutiae of every experience. Because the cognitive capacity of the brain is limited, it does not encode every detail of every event, but it filters them to extract their meaning; it is from this that it recreates a replica of reality which it stores, and which we reconstruct each time we attempt to remember.
The first, and perhaps most costly pitfall of memory, is forgetting. Hermann Ebbinghaus was the first to systematically study how humans forget what they have learnt, and he produced the Ebbinghaus forgetting curve which shows that we forget 40% of new information within a few days. The second major pitfall of memory is false memory recollection, even of so-called ‘flashbulb memories’ of vivid events. The significant implications of this are best appreciated in crime forensics; this is illustrated by the large number of rape and murder convictions which were made on the basis of the eyewitness accounts of victims, but which were subsequently overturned when DNA evidence was applied to historical cases of miscarriages of justice. A third significant pitfall of memory which is relevant to healthcare is failure of source memory, and this is when people remember an event but do not recollect the context in which it occurred, or when they misattribute the event to the wrong source.
Daniel Shachter excellently captured all the pitfalls of memory in his remarkable book titled The Seven Sins of Memory: How the Mind Forgets and Remembers. Apart from forgetting and false memories, he also explored the following causes of memory failure:
- Susceptibility to suggestion: this has been shown to manifest in some sexual abuse cases
- Blocking or the ‘tip of the tongue‘ phenomenon
- Memory binding: this is when two different memories are recalled as a single experience
- Absent mindedness
- Hindsight bias
- Memory persistence
Whilst memory is useful, its limitations are immense. It would therefore be foolhardy to rely on it when it comes to clinical practice and patient safety.
In our next and final two posts under the remit of the cognitive foundations of human error, we will review the challenges and the potentials of thinking.