Cobra Effect · Learning and memory
Desirable difficulties
The practice that feels hardest is often the practice that sticks.
6 cards, read aloud in 2:33, with a test and sources.
Two students revise for the same exam. One of them feels great.
She rereads her notes, highlights, and everything looks familiar. The other closes the book and tries to write out what he remembers. It is slow, and he gets things wrong. Ask them who is ready and she will say she is. Ask the exam.
Robert Bjork has spent decades on that gap.
He is a memory researcher at UCLA. In 1994 he gave the pattern a name. The conditions that make learning feel easy and fast are often the ones that make it fade. The ones that make it feel hard and slow are often the ones that make it stay.
He called them desirable difficulties.
Not every difficulty. A textbook in a language you can’t read is just difficult. A desirable difficulty is one that makes your memory do work it would otherwise skip. Retrieving instead of rereading. Spreading study over days instead of piling it into one. Mixing up the kinds of problem instead of drilling one at a time.
The painters experiment.
In 2008 Nate Kornell and Bjork showed students paintings by twelve artists and asked them to learn each one’s style. Some saw each artist’s work in a block. Others saw the artists shuffled together. The shuffled group was better at naming the artist of a painting they had never seen. Then the students were asked which method had worked better. Most picked the blocks.
Feeling fluent is not the same as knowing.
Rereading makes the page familiar, and familiarity feels like knowledge. Struggling to recall makes you feel you are failing, at the exact moment the memory is being strengthened. So students choose the method that feels best and learn less. Nobody is being lazy. The feeling is lying.
Make it harder, on purpose, in the right places.
Close the book and write down what you remember before you check. Come back to a topic after a gap, when it has started to fade. Mix the kinds of problem in one sitting. If revision feels smooth, be suspicious. If it feels like a struggle you are slowly winning, that is what learning feels like from the inside.
Sources
- Desirable difficulty, Wikipedia. Bjork’s term, the main kinds of difficulty that help, and the studies behind each one.
- Make It Stick, Peter Brown, Henry Roediger and Mark McDaniel, 2014. The readable book on this research, written with two of the researchers. Retrieval, spacing, interleaving and the illusion of fluency, each with the evidence.
- Bjork Learning and Forgetting Lab, UCLA. Robert and Elizabeth Bjork’s lab site, with plain summaries of the research and links to the papers, including the 2008 painters study.
Nearby ideas
- The spacing effect. Spread your study out over time and it lasts far longer.
- The Dunning Kruger effect. Why the least skilled are often the worst judges of their skill.
- Regression to the mean. Extreme results drift back towards normal, whatever you do.
- Interleaving. Mixing problem types feels worse and teaches better.
- The Feynman technique. If you cannot explain it simply, you have found a gap.
- Chunking. Experts see patterns where beginners see pieces.
- Deliberate practice. Hours alone do not build skill. Focused work on weaknesses does.
- The method of loci. Pin what you need to remember to a place you already know.