accessibility of knowledge in memory

n. Knowledge accessibility is the ease with which a unit of previously acquired knowledge comes to mind. This knowledge could consist of a single concept or a configuration of interrelated concepts (a schema), a proposition or social norm, a past experience and the affect associated with the experience, or a procedure for attaining a particular goal. The accessibility of a particular unit of knowledge can be inferred from the time required to perform a task in which the knowledge is required or, alternatively, the likelihood that it is used rather than other knowledge that is equally or more applicable.
The importance of knowledge accessibility derives from the fact that when individuals are called upon to make a judgment or decision, they rarely consider all of the knowledge they have accessible in memory that potentially bears on it. Rather, they typically use the subset of relevant knowledge that comes to mind most easily without considering other, less accessible concepts and information that might also be applicable. Thus, when several units of knowledge are equally applicable for accomplishing a particular purpose (interpreting a piece of information, making a judgment, performing a certain task, etc.), the knowledge that is most accessible in memory is most likely to be used.
Theoretical underpinnings. Conceptualizations of the impact of knowledge accessibility are rooted in more general theories of memory. These theories are typically metaphorical and do not pretend to describe how knowledge is actually represented in memory. Connectionist models, which assume that knowledge is distributed throughout the memory system rather than stored in a specific location, may ultimately provide more valid descriptions of knowledge accessibility phenomena. At this writing, however, these models have not been sufficiently well developed to generate clear a priori predictions.
One conceptualization of knowledge accessibility is based on a spreading activation model of associative memory. According to this model, units of knowledge are connected in memory by associative pathways, with the length of the path (an indication of the strength of the association) decreasing with the number of times that the units have been thought about in relation to one another. When one knowledge unit is activated (i.e., thought about), excitation spreads from the unit along the pathways that connect it to other units, and when the excitation that accumulates at one of these locations exceeds a given activation threshold, it is activated as well. When a unit of knowledge is no longer thought about, the excitation that has accumulated at the unit gradually dissipates. However, as long as some residual excitation still exists, less excitation from other sources is required to reactivate it. Thus, it is more likely to come to mind.
A second conceptualization assumes that units of knowledge about a particular referent are stored in memory in a stack (e.g., a bin) pertaining to this referent. Whenever a unit of knowledge about the referent is used, a copy of it is deposited in the bin that pertains to its referent. Thus, the more often it is used, the more copies of it exist. Moreover, recently deposited copies are on top of the stack. When information about the referent is required, the bin is identified and a probabilistic, top- down search is performed. Thus, the more recently deposited knowledge units are more likely to be retrieved. Because the search is imperfect, however, relevant units of knowledge can often be missed. Therefore, the number of times a unit of knowledge has been used in the past (and thus the number of copies that are contained in the bin) is also a determinant of the likelihood of retrieving it.
Determinants. Two determinants of knowledge accessibility are implied by the theories of memory just described: the recency with which a unit of knowledge has been used in the past and the frequency with which it has been used. First, concepts or units of knowledge that have been used a short time before people are called upon to make a judgment or decision may influence this judgment, whereas other cognitive material, although equally applicable, may be ignored. To give an example, people who are asked to form an impression of someone who wants to cross the Atlantic in a sailboat are more likely to interpret the behavior as foolhardy, and to evaluate the person unfavorably, if they have recently encountered the term reckless in the course of performing an unrelated activity than if they have encountered the term adventurous.
The effect of recency is short lived, however, whereas the effects of frequency are more enduring. Concepts and knowledge that have been drawn upon frequently can become chronically accessible in memory and thus may have a disproportionate influence on judgments and behavior in situations in which they are applicable. Cultural and social factors that influence the frequency of encountering a concept or normative standard may increase the likelihood of applying it in making judgments and decisions despite the fact that alternative criteria are available in memory and equally applicable. The effect of recently activated knowledge can override the effect of chronic accessibility a short time after the knowledge has been activated. However, activation frequency is likely to predominate after time has elapsed.
Other factors can also influence the accessibility of knowledge in memory. For example, thinking extensively about stimuli at the time they are encountered, because of their novelty, vividness, or inconsistency with expectations, can increase the ease with which they later come to mind.
Effects. The accessibility of concepts and knowledge can affect judgments and decisions through their mediating influence at several stages of processing. When new stimulus information is received, an existing concept whose features are similar to those of the information is likely to be retrieved from memory for use in interpreting it. When more than one such concept is applicable, however, the one that is most easily accessible is the more likely to be used. Similarly, people who are asked to report their belief about an event or the existence of a particular state of affairs, or to indicate their attitude toward a person, object, or event, may often search memory for information with implications for this judgment. In these cases, the first relevant information that one identifies is most likely to be applied, and other, equally relevant but less accessible information may have less effect. (As a simple example, people are more likely to report that drinking coffee is desirable if they are asked in the morning, when thoughts about the desirability of being alert are likely to be activated, than if they are asked late at night when they are trying to fall asleep. Alternatively, they are more likely to evaluate a U.S. president favorably if they are asked a short time after hearing a speech in which he/she has espoused a position they like than if time has elapsed and other, less desirable positions come to mind.)
The use of various cognitive procedures (e.g., the disposition to focus on positive as opposed to negative consequences of a behavior when deciding whether or not to engage in it) can also depend on the accessibility of these procedures in memory. On the other hand, concepts that happen to be accessible in memory can have a direct impact on behavior. John Bargh and his colleagues, for example, found that exposing college-age participants to concepts associated with the elderly led them to walk more slowly to the elevator after leaving the experiment.
Demonstrations of the effects of knowledge accessibility have generally focused on the impact of semantic concepts and knowledge. However, the affective reactions that are associated with this knowledge can have similar effects. For example, people who feel happy or unhappy as a result of recalling a pleasant or unpleasant past experience might misattribute these feelings to a stimulus they encounter subsequently, leading them to evaluate the stimulus either more favorably or more unfavorably than they otherwise would.
The role of awareness. People who are called upon to make a judgment or decision typically assume that the knowledge that comes to mind is determined by the type of judgment or decision they have to make and do not consider the possibility that other, objectively irrelevant factors might also have an influence. In some cases they may not be aware of these factors at all. Several studies show that subliminally exposing participants to a specific set of concepts, thereby increasing the concepts’ accessibility in memory, increases the likelihood that these concepts are applied to information they later encounter in an unrelated situation. Even when people are aware of the concepts they have employed in a situation, however, they may not attribute the accessibility of these concepts to this situation when they come to mind at a later point in time. Consequently, for example, experimental participants report stronger beliefs in a hypothetical event if they have previously encountered a statement about the event in an opinion questionnaire they completed some time earlier. Alternatively, they are more likely to judge a fictitious name to be that of a well-known public figure if they have encountered the name in a different experiment 24 hours earlier. In each case, people may attribute the ease of retrieving this knowledge to having encountered it in other, nonlaboratory contexts, thus inferring that the event or name is generally well known. In fact, people may often base their judgment of the frequency of occurrence of an event on the ease with which an instance of the event comes to mind, independently of other considerations. By the same token, experiencing difficulty in retrieving knowledge in support of a particular proposition may be used as an indication that the proposition is invalid.
When people are aware that the accessibility of knowledge in memory might be due to factors that are irrelevant to a stimulus they are judging, they may sometimes discount it or seek alternative bases for the judgment. However, this may occur only if they are both motivated and able to conduct this search. Individuals who are aware they have used a trait concept in performing an initial task might sometimes avoid using the concept to interpret the information they receive in an unrelated task they perform subsequently. If they are distracted from thinking about the judgment they are asked to make, however, or if they are chronically unmotivated to devote thought to the task, they might use the activated concept as a basis for judgment despite their awareness that its use may be biased by extraneous factors. - RSW