From NPR, this is Hidden Brain, I'm Shankar Vedantam.

Almost a century and a half ago, a young German philosopher named Herman Ebinghaus picked up a

curious book at a used bookstore. It was called Elements of Psychophysics and it described how to

gather data on invisible mental processes. The book gave Ebinghaus an idea.

And he thinks about, okay, well, we all have this experience of learning information and

forgetting information. How can I study that?

Psychologist Ayanna Thomas. She says Ebinghaus wanted to answer a big question.

How does memory work? He really wanted to understand to 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? This was the late 1800s. There was no protocol on how to run a

psychology experiment. Most insights about memory came from philosophers and theologians.

So Ebinghaus came up with a plan. He would 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 at the exact same rate, in the same soft tone of voice,

keeping time to a ticking metronome. He would read a group of cards aloud once,

hide it, and then try to recite it from memory. Every time he made a mistake, he would stop,

note it in his records, and start over. He kept doing this, stopping and starting over,

stopping and starting over, until he could recite a group of syllables perfectly.

He repeated this process periodically to see how much he could remember, 20 minutes later,

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