Passive review is the opposite of active recall, in which the learning material is processed passively (e.g. by reading, watching, etc.).
For example, to improve your memory through passive review, you learn in this way: you read a text today; to not forget it, you repeat it tomorrow and then you repeat 4 days later and then 8, 16, 32, 64, etc., days later. You don't ask yourself to explain the content of the text, but only reread the content. If you think to recall something, you are more likely to keep it in your memory. Passive review is a simple method but it is not as effective. Active recall is more complicated and difficult (because it forces you to recall something) but it is highly effective.
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