Memory and mood: Negative emotions nullify a problem with recall

Imagine a critical witness being grilled in preparation for a high-profile murder case. The prosecuting attorney wants to make sure she has every angle covered, so she questions the witness over and over to double- and triple-check that he has his story right. When he finally takes the stand, he remembers every detail she asked him about. But when the defense attorney cross-examines him, she takes an unexpected new tactic, asking about details the prosecutor hadn't prepared him for. He stumbles over some of the answers, contradicting other witnesses, and now all his testimony seems suspect. Was he lying?

Perhaps not. In similar situations, researchers have found that when we practice remembering only part of a group of related items, we're more likely to forget the rest of the items in the group. For example, suppose you're asked to remember these two lists:

Then later you practice on just half the fruits you memorized (say, Watermelon, Strawberry, Mango, and Cantaloupe). Finally, you're tested on your memory of items from both lists. Of course, you'll remember the items you practiced best. But you'll remember the drinks you didn't practice better than the fruits you didn't practice. By practicing on only some of the fruit, you actually forgot more of the fruits you didn't practice than you would have if you hadn't practiced at all.

But memory is complicated, and researchers have found that your emotion and mood when forming the memories can affect what you recollect. Karl-Heinz Bäuml and Christof Kuhbandner wondered if emotions while practicing would also affect recall.

They asked 27 student volunteers to remember similar short lists of words. Then, one of three moods was induced using graphic photographs: Diseases, mutilated bodies (for negative moods) erotic scenes, babies (positive), scenery, or objects (neutral). Next, the practiced recalling half of the words in one category by being presented with the category name and the stem of the word (for example, "Fruit Man___"). Then they were assessed to ensure that the proper mood had been induced. Finally they were shown the category and just the first letter of all the words ("Fruit C________," "Drink V_______," and so on). Did mood during practice have an effect on the results? Yep:

The key thing to notice here is the yellow bars. When the participants were in a neutral or positive mood, they recalled fewer of the words from the category they had practiced, compared to the category they didn't practice. When they were in in a negative mood, the category of the words they practiced didn't matter at all: all that mattered was whether they had practiced.

So being in a negative mood during practice nullifies the problem of practicing only part of the items from a category: Normally practicing "fruit" words, for example, impairs your memory of the fruits you didn't practice compared to words in other categories like "drinks." But the negative mood seems to remove the effect completely.

The researchers don't offer an explanation for why this might occur, other than to note that mood can effect how we form memories, and this is one way that it does. It's a good thing to keep in mind when you're making judgments about the accuracy of the memories of others.

Bäuml, K., & Kuhbandner, C. (2007). Remembering Can Cause Forgetting--but Not in Negative Moods Psychological Science, 18 (2), 111-115 DOI: 10.1111/j.1467-9280.2007.01857.x