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You studied the chapter. You knew the answer last night. In the exam hall it is gone, and then it comes back ten minutes after you hand in the paper. Endel Tulving spent fifty years studying exactly this. His work explains why it happens and what kind of revision makes it happen less.
Who was Endel Tulving?
Tulving was born in Estonia in 1927, spent several years in post-war Europe and emigrated to Canada in the late 1940s. According to his Royal Society biographical memoir, he took degrees at the University of Toronto and Harvard and returned to Toronto as a faculty member in 1956. The memoir describes him as an independent thinker who rejected the dominant view of memory as a chain of associations and treated memory as organised and actively retrieved. He died on 11 September 2023.
Is forgetting the same as losing the memory?
Tulving's answer was no. In Availability versus accessibility of information in memory for words (1966), he and Zena Pearlstone gave students lists of words that belonged to named categories. The lists had 12, 24 or 48 words. The participants, high-school students in Toronto, then tried to recall the words, some with the category names in front of them and some without.
Cued recall was higher than recall without cues, and the gap grew as the lists got longer. The words the uncued group "forgot" were still in memory. They were available but not accessible. The right cue brought them back.
This is the blank in the exam hall. The formula is stored, but the cue you learned it with (the page, the heading, the worked example) is missing, and the question gives you a different one.
What are episodic and semantic memory?
In a 1972 chapter titled Episodic and Semantic Memory, Tulving proposed that these are two partly overlapping systems. A summary on the archive of his work puts it this way: episodic memory deals with personal experiences and when they happened, while semantic memory deals with the meanings of words and concepts.
When you remember the afternoon your teacher dropped a magnet through a copper pipe, that is episodic. When you know that a changing magnetic flux induces a current, that is semantic. In his 2002 review in the Annual Review of Psychology, Tulving described how the idea grew to include a sense of self and of travelling back in subjective time, with support from studies of people with brain damage and from brain imaging.
Why does the way you study change what you can recall?
With Donald Thomson, Tulving proposed the encoding specificity principle (1973): what is stored depends on how you processed something when you learned it, and that in turn decides which cues will work later. A cue helps only if it overlaps with what you laid down.
Around the same time, in ten experiments with Fergus Craik (1975), people answered questions about words. Some questions were about the typeface, some about rhymes and some about meaning, such as whether the word fitted a sentence. Words processed for meaning were remembered better on a surprise test, even when the shallow task took longer.
For a student, the two findings fit together. Thinking about what a formula means gives you more ways to reach it. Copying it out in neat handwriting gives you very few.
What can a student take from Tulving's way of working?
Tulving kept asking what a memory test actually measures. You can ask the same about your own revision.
Practise with exam-style cues. Rereading a chapter in order uses the textbook's cues. Close the book and answer questions phrased the way a paper would phrase them. Our guide to flashcards that work shows how to write them.
Organise into categories. The 1966 students recalled more when they had category names. Group your formulas or reactions under headings you can write from memory, then recall the items under each heading.
Process for meaning. For each formula, say what each symbol stands for and when the formula fails. That is the deeper processing Craik and Tulving tested.
Vary where and how you revise. If you always revise at the same desk with the same notes, your cues are narrow. Our post on changing where you study looks at the evidence.
When you blank, cue yourself. Write the chapter name, sketch the diagram, or list the quantities in the question. Each one is a possible way back to what you stored.
If you are not sure which ideas you can actually retrieve, Fermi's AI tutor checks understanding as it goes and works out what you already know, so a gap shows up in practice rather than in the exam. Memory can also be wrong rather than missing, which is the subject of our post on Elizabeth Loftus and how memories can be changed.
Tonight, pick one chapter, write its main headings from memory, and recall everything you can under each one before you open the book.
