Retrieval-induced forgetting

Retrieval-induced forgetting (or RIF) is a phenomenon in memory where the act of remembering causes forgetting of other information in memory. The phenomenon was first empirically demonstrated in 1994, although the plausibility of such an effect was previously alluded to in discussions of retrieval inhibition. Often demonstrated through an experiment called the retrieval-practice paradigm, RIF has been shown to be generalizable to many kinds of materials.

Although RIF occurs as a consequence of explicit retrieval, the actual forgetting is thought to occur implicitly or below the level of awareness. Currently, there is ongoing debate among cognitive psychologists over different theoretical accounts that best explain why RIF occurs, and how the effect fits in the larger picture of cognition. In particular, researchers are divided on the idea that an inhibitory mechanism may be responsible for the resulting forgetting, as opposed to general interference from other information in memory.

Prior and related research
Although the term "retrieval-induced forgetting" was first used in 1994, the plausibility of RIF was described in an earlier review of inhibition by Robert A. Bjork:

"...Neely and Durgunoğlu (1985) account for inhibited (slowed) episodic recognition of words following a semantically related prime in terms of a suppression-type retrieval inhibition. They assume that 'subjects actively tried to suppress the prime's semantic associates in the episodic recognition task because the retrieval of such associates was irrelevant to the task&mdash; namely, knowing that a target is semantically related to its prime does not provide information as to its study status.'"

Conceptually, RIF is similar to observations of part-set cuing in that both show lowered memory performance given a subset of previously studied information. For example, in part-set cuing when participants are given a subset of U.S. states and then asked to recall as many states as possible, they typically perform worse compared to when no subset is given beforehand. In the field of memory inhibition, RIF is also to related forgetting attributable to changes in context in the sense that they are initiated relatively automatically and without awareness. Output interference is also a related phenomenon, where generation of exemplars from a category (like fruits) can render the remaining items from the category less accessible either through slowed or errors in generation.

Retrieval-practice paradigm
RIF is demonstrated in a type of experiment called the retrieval-practice paradigm. The exact nature of instructions and procedure varies slightly from experiment to experiment. For instance, in the original version of the experiment, booklets were used to present stimuli and to facilitate memory testing. However, since then this procedure has often been done using computer software such as Microsoft PowerPoint or E-Prime. There are typically three main phases:

Study phase
Participants are asked to study word pairs called category-exemplar pairs that consist of a category name and a word that belongs to that category (for example, FRUIT - orange). Instructions are given to study the items, although the specific strategy for study can vary across experiments, as can the amount of time participants are given to study each item. Typically, multiple exemplars are studied that are split over a number of categories (e.g. Anderson et al. (1994) used 48 items in total— 8 categories with 6 items in each category). For example, among several others, participants might study word pairs such as the following:
 * METAL - iron
 * TREE - birch
 * METAL - silver
 * TREE - elm

Retrieval-practice phase
A subset of the items, typically half of the items from half of the categories, are tested through a fill-in-the-blank test. For a given item, the participant is shown the category name and the first two letters of a studied word from that category followed by a blank (e.g. METAL - ir______). Participants are instructed to fill in the blank with the name of a previously studied word from that category. There are usually three repetitions of retrieval-practice, so participants will practice remembering the items multiple times. For instance, using the above examples, participants may only receive practice for the pair METAL - iron. The retrieval-practice phase splits the item into three different types that are of interest during the final test, and are often denoted using the following notation:
 * Rp+ items (Practiced items) are studied words that participants attempt to remember during retrieval practice.
 * Rp- items (Unpracticed, related items) are studied words that are not practiced, but related (by category) to words that were practiced.
 * NRp items (Unpracticed, unrelated items) are studied words in categories that are never practiced. These categories are typically unrelated to practiced categories.

As an example, consider a participant who has studied the following items:
 * METAL - iron
 * TREE - birch
 * METAL - silver
 * TREE - elm

The participant performs retrieval practice for iron, but not for any of the other above items. The items would be designated as following:
 * Rp+ items: iron
 * Rp- items: silver
 * NRp items: birch, elm

Test phase
After retrieval-practice, participants are given a final test, where participants are asked to remember all the items from the study phase. The goal of the test phase is to assess whether participants remember Rp- items any differently than NRp items. Another way of thinking about this goal is whether, at final test, prior retrieval practice had any effect on related items compared to unrelated studied items. RIF is ultimately measured as the difference between the proportion of Rp- items remembered and the proportion of NRp items remembered.

Researchers have employed several versions of the test phase in the RIF literature:

Category-cued tests
Participants are shown one studied category at a time and are asked to remember all studied items from that category. Although a set amount of time is given for each category, the exact amount of time varies across studies. For instance, Anderson et al. (1994) gave participants 30 seconds for each category cue (and given that there were 6 words in each category, this meant that participants had 5 seconds, on average, to remember each item). Other studies have used longer durations.

Category-plus-stem-cued tests
In addition to the category, participants are also given a particular number of letters corresponding to a uniquely studied item from the category. Because these cues are specific to a particular word, participants are given relatively less time to respond to each cue compared to category-cued tests. Test durations for each cue have ranged anywhere from 10 seconds to as few as 3 seconds. Typically, category-plus-stem-cued tests include only the first initial letter from the word, but others have included multiple letters.

Recognition tests
Recognition tests are unique in that participants are not required to produce a word from memory as a part of the test. Instead, participants are literally shown a word, and are asked to report whether it was a word they studied or not. In addition to showing all of the studied words, recognition tests typically show a large number of non-studied words. Consequently, not only is it typical to measure how often participants correctly recognize studied items (called hits), but also how often they incorrectly recognize non-studied items (called false alarms). Comparing the difference between these two proportions is called d', a statistic measuring the ability to discriminate between studied and non-studied items, and has been used to represent RIF. Reaction time is also used to represent RIF, where slower reaction times are thought to represent more difficulty in recognizing the studied item.

General findings
RIF studies have generally yielded results where, on average, Rp- items are remembered less well than NRp items, the latter of which serves as a baseline. That is, unstudied items that are related to practiced items are remembered less well than unstudied items that are unrelated to practiced items. A secondary finding is that, on average, practiced words (Rp+ items) are remembered much better at test than baseline. This result is the product of the testing effect stemming from retrieval practice.

Generality of RIF
RIF studies have generally used words from basic and easily recognized categories, but the effects have been shown with a wide variety of stimuli:
 * Homographs
 * Words based on their lexical properties
 * Visuo-spatial information
 * Propositional information
 * Details of a mock crime scene
 * Personality traits of others

Manipulation of retrieval practice phase
Although the typical paradigm includes retrieval practice of previously studied words, some studies have show RIF even when participants are asked to retrieve something else. For instance, RIF has occurred even when participants generate new, unstudied items from previously studied categories in what is called "extra-list retrieval practice" or "semantic generation." In a method called "impossible retrieval practice," RIF has also been observed when participants are asked to generate a word for a category, even though one does not actually exist. Consider that having studied a number of fruits, a participant is asked to generate a word given the cue FRUIT - wu. Although successful retrieval is not possible in this case, RIF is still observed at final test.

When retrieval practice is replaced with additional study
Some studies have examined the effect on RIF when participants, instead of being asked to perform retrieval practice, are given additional study trials. That is, participants actually restudy the material instead of remembering prior information. In these cases, participants have failed to show any RIF effects.

RIF studies in special populations
Because RIF is an effect related to the accessibility of information, researchers have studied whether it persists in populations that have certain disorders related to memory. In one study of students diagnosed with ADHD, the degree of RIF observed compared to a control group depended on the kind of final test used. When using a category-cued test, there were no differences in RIF compared to a control group. However, when a category-plus-stem-cued test was used, participants with ADHD, on average, showed less RIF than controls. Patients with depression do no show any RIF compared to controls when using a category-plus-stem-cued test. Patients with schizophrenia have also been shown to produce comparable RIF effects to control groups under a category-cued test, but show reduced RIF using a recognition test.

Socially shared RIF
Collaborative studying is thought to have certain benefits, such as helping one remember some forgotten details, and reducing errors that may be picked up by other group members. However, when comparing retrieval of a list of studied items between individuals and groups (of three), groups performed worse on average. This effect is called socially shared RIF, and can even occur with details related to flashbulb memories, such as Americans remembering details related to the September 11th attacks.

Interference
In general, forgetting is often accounted by interference processes owing to the heightened accessibility of other, associated information in memory. In relation to RIF, researchers have described interference through a number of possible mechanisms. For instance, one theory called blocking posits that because Rp+ items are more easily remembered at test, they may occupy a "response channel" in memory and effectively prevent Rp- items in memory from being remembered, but would not affect their accessibility. NRp items would less affected by this blocking effect because retrieval of Rp+ items would not block out items from different categories. Other theories such as resource diffusion and response decrement are similar to blocking. However, these theories conceptualize memory as a finite set of resources that cannot be distributed adequately enough to Rp- items at test.

Other models of interference have been proposed that more precisely define the idea of an item's strength in memory through separating the strength of item information and the contextual information it is linked to. Such models may explain why certain strengthening methods cause RIF and others do not.

Inhibition
Central to the inhibition account of RIF is that access to Rp- items is actively suppressed by an inhibitory process during retrieval-practice. For instance, when participants perform retrieval practice, the category cue may activate many associated items. The degree to which related, but inappropriate associates (i.e. Rp- items) become accessible serves as a source of competition that antagonizes retrieval of an appropriate response. To resolve this competition, an inhibitory process intervenes to suppress accessibility to such items. Subsequently, this suppression facilitates retrieval of an appropriate item and prevents retrieval of contextually inappropriate items. Items from unrelated categories (i.e. NRp items) are less competitive during retrieval practice and thus, require less inhibition. At final test, the consequences of the suppression persist, and previously competitive items that were inhibited are less accessible.

This reduction in accessibility is consistent with the definition of inhibition proposed by Robert A. Bjork: That inhibition is an active, direct form of suppression that serves to reduce access to one or several responses for some adaptive purpose.

Memory inhibition in reference to RIF has sometimes been likened to processes of inhibition known to be in motor control, such as those responsible for a baseball player stopping their swing when they anticipate a ball, or removing one's hand from a hot stove. Similarly, when a dominant response in memory is inappropriate, inhibitory processes must be recruited to temporarily suppress that response so that a more appropriate one can be retrieved.

Other accounts
Individual strategies in retrieval have been considered as one way RIF might occur, in that retrieval practice may disrupt the way participants remember items studied from those categories. If participants are preparing to remember items during retrieval-practice based on some strategy, certain presentation orders may disrupt that strategy whereas others may not. For instance, when participants practice items in the same or comparable order as presented during study, RIF is lowered compared to when presentation is random during retrieval practice. This pattern of results is the same regardless if participants are instructed to remember the order in which items are presented during study.