SOURCE MONITORING

Source monitoring refers to cognitive processes involved in making attributions about the origins of mental experiences; for example, attributing a mental experience to something dreamed, something imagined, or a perceived event. The concept of source memory overlaps with, but is more general than, the idea of memory for context. Source monitoring is an important aspect of everyday cognition, for example, in deciding whether one took one's medication or just thought about taking it, read about a space alien invasion in a tabloid or a news magazine, or really saw the defendant at the crime scene with a knife or just heard about the knife later. Errors in source monitoring range from the trivial (telling a joke to the same person you heard it from) to the egregious (mistaking a memory of a dream of being sexually abused for a memory of a real event from childhood).

Marcia Johnson and her colleagues (1993) have detailed a theoretical framework for understanding the cognitive processes and factors that influence source memory. According to the source monitoring framework, any given mental experience typically does not include a single feature or tag or label specifying what it is (e.g., a memory of a dream, an imagination, a perception). Rather, people attribute some mental experiences to memories based on the experience's features. Events have many features (objects, location, people, color, taste, emotions, ongoing thoughts), some of which are encoded in memory; a few or many of these features may be brought to mind (reactivated) after only a few minutes or years later. What a person calls that later mental experience depends on what features it includes and on the person's beliefs about the differences between mental experiences from different sources. For example, people usually expect memories for events (sometimes called episodic memory) to contain details reflecting such aspects as the who, what, when, where, why, and how of the event. A mental experience that does not have such details might be attributed to, for example, inference, general knowledge, or belief, depending on the particular features it does have.

Different types of encoding processes (e.g., seeing, hearing, thinking, dreaming) and different types of events (e.g., movie, telephone call) tend to produce memorial representations that are characteristically different from each other. For example, memories of imagined events typically have less vivid perceptual, temporal, and spatial information than perceived events and more information about intentional cognitive operations (e.g., actively generating images while thinking). Therefore, if a mental experience had substantial perceptual detail, one would tend to attribute it to a perceived event (e.g., something one saw). However, there is variability among memories from any particular source, and the distributions of features from different sources overlap. For example, some dreams are more vivid or plausible than some waking events. Thus, remembering always involves evaluating the quality and quantity of activated characteristics in light of expectations about typical characteristics of mental experiences from various sources.

Source attributions are often made rapidly and without deliberation based on heuristic judgments about activated features. However, source monitoring sometimes entails more systematic processes that are typically slower and more deliberate, including retrieving additional information, extended reasoning, and so on. For example, a vivid memory of Frank talking to Paul at a party might be contradicted by retrieving additional information that places Frank out of town at the time of the party. Similar distinctions between relatively automatic and more controlled processes of remembering have been made by L. Hasher and R. Zacks (1979), L. Jacoby and C. Kelley (1989), and other researchers. Both heuristic and systematic source attributions are affected by a rememberer's biases, goals, agendas, and meta-memory beliefs. For example, one will usually engage more systematic source monitoring processes if the cost of a mistake is high, but engage only relatively automatic, heuristic processes for most everyday remembering.

Historical Context

The concept of reality monitoring was introduced in the early 1980s by M. K. Johnson and C. L. Raye (1981) to explain how memories for internal events (e.g., thoughts, imaginations) are discriminated from memories for external, perceived events, and why they are sometimes confused. This concept was subsumed by the more general source monitoring framework in the early 1990s. The theoretical ideas incorporated in the source monitoring framework were proposed to help organize and understand diverse findings and guide additional research. For example, studies in the 1950s and 1960s showed that people falsely recall (Deese, 1959) or falsely recognize (Underwood, 1965) associates of presented words: Hearing thread, haystack, sharp, and so on, can lead people to misremember hearing needle, presumably because they thought of needle during study and later mistake the thought for an actual presentation of the word. In the 1970s, M. K. Johnson and J. D. Bransford and colleagues (1973) showed that people falsely recognize ideas that were only implied in sentences. For example, after hearing, "The man dropped the delicate glass pitcher on the floor" people often remember hearing, "The man broke the delicate glass pitcher on the floor." The 1970s and 1980s produced many studies showing that people's memory for experiences tends to be shaped by their expectations or schemas (see Alba and Hasher, 1983, for a review). For example, W. F. Brewer and J. C. Treyens (1981) showed that people who had briefly waited in an office were likely to falsely remember items such as books, which were not in the office but might be expected to be, and to not remember unexpected items that were there (e.g., a skull). E. F. Loftus and colleagues (1978) showed that information introduced when people were questioned about an event was later sometimes (mis)remembered as part of the original event.

Such findings illustrate that people confuse information from different sources. For example, as part of their normal comprehension processes, people think of related information during encoding or remembering (or both) and misattribute this information to the actual event. Other times, they confuse what they saw with what they heard or read, or confuse two similar experiences. Yet, sometimes memory is quite accurate. The source monitoring framework specifies the factors that influence the likelihood that memory will be accurate or distorted.

Factors Affecting Source Monitoring

Source monitoring depends on the type, amount, and quality of activated information, the extent to which the active information helps uniquely specify the source, the judgment processes engaged, the weights assigned to different features, and the criteria used when making the source attribution. Neither the activated features (representations) nor the processes that act on them are perfect, and thus errors occur. A basic tenet of the source monitoring framework is that inaccurate source monitoring (sometimes called source confusions, source misattributions, source errors, source amnesia, source forgetting, memory distortions, or false memories) and accurate source monitoring arise via the same mechanisms.

Anything that disrupts the encoding, consolidation, or retention of the features of events will negatively affect source monitoring. For example, at encoding, divided attention or focusing on one's own emotions rather than event details can increase source monitoring errors, presumably because useful source-specifying information fails to be, or is weakly, bound to other features of the event. Errors increase when the diagnosticity of available source information is reduced, for example, when semantic or perceptual similarity between events from different sources is increased. Errors also increase when more lax criteria are used to evaluate mental experiences, features are weighted inappropriately, attention is divided at test, or the time that is available to make a source judgment is limited. Individual motives and the social/cultural context can influence all of these factors.

The general view that remembering is not a simple matter of "retrieving" memory traces but rather a subjective experience with phenomenal qualities that differ in important ways has generated new interest in assessing the subjective qualities of memories. One approach asks people to distinguish between items they know and items they remember ; another uses memory characteristics questionnaires to elicit more detailed ratings of features of memories. For example, such studies have shown that, on average, false memories tend to be rated as having less perceptual detail than true memories.

Brain Regions Involved in Source Monitoring

Neuroimaging data (e.g., from functional magnetic resonance imaging) together with neuropsychological studies of brain damaged patients with amnesia indicate that the hippocampus plays a central role in the binding of features into complex representations—a process critical for later source monitoring. Profound disruptions in source monitoring, such as delusions, hallucinations, and confabulations, can arise from damage to frontal brain regions, indicating that these regions are critical for source monitoring. Neuroimaging studies that show activation of frontal regions during source monitoring in healthy individuals provide converging evidence. Children and older adults have more difficulty with source monitoring than do college-aged adults, particularly as the similarity of the sources increases. Researchers have suggested that such findings may reflect the relatively late maturation of frontal functions in children and the increased probability of pathology in frontal regions associated with aging. One goal of current neuroimaging work is to more clearly delineate the brain circuits underlying the encoding, revival, and evaluation of memories.

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Marcia K.Johnson

Karen J.Mitchell