This is Hidden Brain, I'm Shankar Vedantam.

Memory is the diary we all carry about with us.

Oscar Wilde wrote those lines in his play, the importance of being earnest.

There's something deeply comforting about this idea, that memory is like a diary we can open and review.

But is this really how our minds work?

More than a century ago, a young German philosopher named Herman Ebinghaus

wanted to figure out how we retain information.

He really wanted to understand memory at its most basic core.

How quickly can we learn?

New information that we've never been exposed to, and how quickly does that information degrade.

Psychologist Ayanna Thomas.

She says Herman Ebinghaus decided to run an experiment on himself.

First, he needed something to memorize.

He came up with the idea of nonsense syllables, three random letters strung together.

He put them on some cards.

So more than 2000 of these.

Then he shuffled the cards, divided them into groups, and set about learning them in a variety of controlled conditions.

Sometimes, he read the cards aloud, forcing himself to read them in the exact same rate, in the same soft tone of voice,

keeping time to a ticking metronome.

Every time he made a mistake, he would stop, note it in his records, and start over.

Like move, walk.

He repeated this process periodically to see how much he could remember 20 minutes later, an hour later, nine hours, a day, and so on.

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