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I know that I went out for dinner last month, but I can鈥檛 remember anything about the experience

How much we remember of events we have experienced seems to fall on a spectrum. At one extreme, some individuals are unable to form these kinds of memories at all. 鈥淧eople with severely deficient autobiographical memory syndrome would report an awareness of the fact they were at the dinner, but they don鈥檛 have a feeling of re-experiencing it. It鈥檚 more of a factual memory,鈥� says neuropsychologist Brian Levine in Toronto.

At the opposite end of the spectrum are those with 鈥渉igher superior autobiographical memories鈥�, who can recall in precise detail events from decades ago. The best-known case is that of a woman called Jill Price, who can recall most days of her life from the age of 11. The majority of us fall somewhere in between. Strong autobiographical memory skills are linked to the ability to form , and probably to a .

Random memories pop spontaneously into my mind all the time

Known as 鈥渕ind pops鈥�, these involuntary recalls happen to all of us, on average about 20 times a day, although there is a lot of variation between individuals. 鈥淚t鈥檚 a basic characteristic of autobiographical memory,鈥� says Dorthe Berntsen of Aarhus University in Denmark, who studies this phenomenon. Once they pop into your head, they soon disappear. 鈥淭hey鈥檙e like dreams 鈥� if you don鈥檛 write them down, you forget all about them,鈥� Berntsen says.

and retrieve fewer memories consciously, perhaps because we find it harder to inhibit thoughts as we get older. Berntsen鈥檚 work shows that they tend not to spring up when we are focused on a task, but are more likely to appear in dull moments. She thinks that, far from being an unwanted distraction, they are an important component of daily functioning.

These involuntary memories are often associated with the environment we are in, and there is a high probability they have relevance to the ongoing situation, she says. 鈥淭hey can give you an update, reminding you that last time you were in this situation you did this or that,鈥� she says. But they are also cheap. 鈥淭hey don鈥檛 require the parts of the brain that require effort 鈥� executive functioning. If they are not relevant, you don鈥檛 have to think about them,鈥� Berntsen says.

I can remember facts, but am rubbish at faces

You might come across as rude if you don鈥檛 remember people, but don鈥檛 beat yourself up about it, everybody鈥檚 memory is different. This could be down to innate differences in brain wiring. People with prosopagnosia, or face blindness, for example, can鈥檛 easily tell faces apart, even if they belong to people they know well. At the other end of the spectrum are super-recognisers, who have an amazing memory for faces.

鈥淐reating a hard copy of memories in media leaves a diminished copy in our own heads鈥�

For the rest of us, our memory skills (or lack thereof) are more likely to be due to our life experiences and strategies we鈥檝e picked up along the way. Most of us start out with roughly the same memory ability, but 鈥渟ubtle differences at the beginning get amplified by experiences and interests that build on each other. It鈥檚 not intrinsic, it鈥檚 acquired,鈥� says neurologist Barry Gordon at Johns Hopkins University in Baltimore, Maryland.

Expertise, prior knowledge and practice make a big difference . Tests of chess masters, for example, show that they have a superior memory for patterns of pieces on a chessboard, but only for ones that are plausibly found in the game. Their ability to remember random positions is little better than that of novices. And studies on master memorisers who, for instance, can remember thousands of digits of the number pi, show that their superior powers of recall are due to strategies to 鈥渃hunk鈥� information into meaningful groups, not any innate talent for remembering. 鈥淭hey still need sticky notes on the fridge door to remember their shopping list,鈥� says Gordon.

This article appeared in print under the headline 鈥淚s my memory normal?鈥�