Why Learners Sometimes Forget

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Fortunately, we don’t need to remember everything. We probably have no reason to remember the phone number of a florist we called yesterday, the plot of last week’s episode of Friends, or the due date of an assignment we turned in last semester. Much of the information we encounter is, like junk mail, not worth keeping, and forgetting enables us to get rid of needless clutter (D. L. Schacter, 1999).

But sometimes we have trouble recalling what we do need. One possible explanation of “forgetting” is failure to store: Information never reached long-term memory to begin with. Perhaps we didn’t pay attention to a piece of information, so it never went beyond the sensory register. Or perhaps after attending to it, we didn’t continue to process it, so it went no further than working memory. Failure to store is not an explanation of information loss, but it is one possible reason that people who think they have learned something cannot recall it later on (D. L. Schacter, 1999).

Psychologists have offered several explanations of why people actually do forget things they have previously stored in long-term memory. Here we’ll consider four possibilities: failure to retrieve, reconstruction error, interference, and decay.

Failure to Retrieve  A man at the supermarket looks familiar, but you can’t remember who he is or where you met him. He smiles at you and says, “Hi there, nice to see you again.” Gulp. You desperately search your long-term memory for his name, but you have clearly forgotten who he is.

A few days later you have a bowl of chili for dinner. The chili reminds you of the Chili for Charity supper at which you worked a few months back. Of course! You and the man at the supermarket had stood side by side serving chili to hundreds of people that night. Oh yes, you now recall, his name is Melville Herman.

One reason we forget is an inability to retrieve: We can’t locate information stored in long-term memory (e.g., D. L. Schacter, 1999). Sometimes we stumble on the information later, while looking for something else. But sometimes we never do retrieve it, perhaps because we learned it by rote or don’t have sufficient retrieval cues to guide our search in long-term memory.

Reconstruction Error  Retrieval isn’t necessarily an all-or-nothing phenomenon. Sometimes we retrieve part of the information we are seeking from long-term memory but can’t recall the rest. In such situations we may fill in the gaps using our general knowledge and assumptions about the world (Kolodner, 1985; Roediger & McDermott, 2000; P. T. Wilson & Anderson, 1986). But even though the gaps are filled in logically, they aren’t always filled in correctly—a form of forgetting called reconstruction error. 

Interference  Sometimes people can easily retrieve things they’ve learned but don’t know what goes with what. As an example, try the following exercise.

Decay  As noted earlier, some psychologists believe that information probably weakens over time and possibly disappears altogether, especially if it isn’t used very often (Altmann & Gray, 2002; J. R. Anderson, 1995; D. L. Schacter, 1999). Theorists often use the word decay when describing this gradual fading process.

All of these explanations of forgetting underscore the importance of instructional strategies identified earlier: We must make sure students are paying attention, help them relate new material to things they already know, and give them opportunities to review, practice, and apply the material frequently. The Into the Classroom feature “Maximizing Retrieval and Minimizing Forgetting” presents and illustrates several possible strategies.