Download Context and human memory

20-Roediger-Chap20
11/16/06
5:00 PM
Page 111
20
Context and human memory
Steven Smith
Context, most generally defined, is that which surrounds. Something can be
bounded by time, by space, by circumstances and by meaning; hence, the
terms temporal context, environmental context, situational context and semantic
context. How context as a general concept should be defined is not clear
because there are so many different types of context, including those
mentioned above, as well as perceptual context, moods, story plots, tasks, drug
states, and so on. Although unitary stimuli have sometimes been referred to as
‘contexts’, it is usually the case that contexts are composed of many
constituents; contexts are constellations of elements. Contexts can vary in
terms of how rapidly changing they are and, concomitantly, how many events
and objects are subsumed by a context. Whereas the rapidly changing words of
a sentence can serve as context for a single word, a novel can serve as context
for thousands of sentences, and a period of one’s life the context for many
novels. Contexts can vary in terms of how enmeshed they are with the focal
events for which they serve as context. Physical environments that fully engage
people, such as control rooms or sports settings, may provide a high degree of
contextual support for activities that take place there, encouraging a high
degree of mesh with the environmental context, whereas the surrounding
environment in which one carries on an involving phone call or videogame
may have little, if any relation to one’s focal activities.
Context acts as a reference for focal material, and can be used to give perspective, to disambiguate and to interpret. All stimuli can be coded relative to varying
perspectives, and are therefore subject to multiple interpretations. Context
bestows set, a preparedness to respond. Context-induced set can affect cognition
at many levels, such as perceptual sets that influence what is seen or how distant an
object seems, learning sets that can influence how new material is encoded, and
mental sets that can become associated with problem solving when a series of
similar problems are solved with the same algorithm or heuristic. ‘Context’ is an
umbrella term that subsumes other types of knowledge structures that support
specific focused information processing, and that have setting and referential
functions, structures such as schemata, frames, tasks, plans or situations.
20-Roediger-Chap20
112
11/16/06
5:00 PM
Page 112
CONTEXT AND HUMAN MEMORY
Memory is said to be context-dependent because experiences always occur
within contexts, and memories of events depend upon the contexts in which
those experiences occur. The influence of context can be seen both at encoding
and retrieval. Events we experience can become bound to our surrounding
contexts, and more so the more enmeshed are our activities with encoding
contexts. Context can enable or activate memories of previously associated
events, a phenomenon referred to as contextual cuing. Reinstatement of past
contexts can cue memories of events experienced in those contexts, a phenomenon referred to as a context reinstatement effect (e.g. Smith 1979). A particular
episodic memory is more reliably evoked by a context cue if fewer events are
stored in memory in relation to that cue (Watkins and Watkins 1974). Context
reinstatement effects can revive seemingly lost memories, and can be phenomenologically powerful experiences that seem to transport people into their
personal pasts. The limits of such ‘time travel’ experiences, such as the degree
of accurate and false memory triggered by contexts, or the recovery of memories that are temporally or physically proximal to one’s original experience in a
reinstated context, are not known. Context also can be used to verify memory,
i.e. to monitor and attribute the source of retrieved knowledge and experiences, as in episodic recognition. Whereas contextual cuing involves retrieval
of to-be-remembered material in response to contextual cues, source monitoring
involves the reverse, i.e. retrieval of contextual information in response to to-beremembered material.
Mental context, sometimes known as functional (as opposed to nominal)
context, is the cognitive representation of an individual’s context, i.e. context
from the subject’s perspective. Mental context is manipulable by an individual,
and may or may not correspond to physically ambient stimuli. Put more
simply, the context one imagines can be different from one’s current physical
context. Imagined mental contexts can be instantiated or activated, maintained
and used without recourse to ambient environmental conditions during activities such as reminiscing about the past, daydreaming and prospective projection
into future situations. Mental context reinstatement effects can occur when one
imagines a previously experienced context associated with to-be-remembered
material. When someone’s mental context corresponds directly to the ambient
environmental context, that mental context can be a combination of automatically and effortfully processed elements of the environment. Because selfgenerated contexts, as well as other conceptual activities, vie for the same limited
pool of attentional resources that process one’s immediate environment, ambient contextual stimuli can also be suppressed to conserve resources (Glenberg
1997), and their influence supplanted by self-generated mental contexts.
Therefore, the degree to which memories are context dependent (i.e. affected by
20-Roediger-Chap20
11/16/06
5:00 PM
Page 113
CONTEXT AND HUMAN MEMORY
nominal manipulations of the context) is inversely proportional to the degree
of contextual suppression that occurs at encoding and at test (e.g. Smith and
Vela 2001). That is, suppressed environments do not affect encoding and
retrieval.
Two important aspects of the relationship between memory and context are
contextual integration and contextual binding. Because contexts are comprised
of multiple elements, those individual elements can vary in their degree of
integration. Better integrated contexts, especially unitized ones, can be better
memory cues. The way that the brain assembles and integrates contextual
material is fundamentally important to understanding how contexts are
instantiated, how they are maintained and stabilized over time, and how they
are destabilized so that new contexts can be instantiated. Memory of an event
can become bound to a context, resulting in contextual associations.
Contextual binding is at the heart of the two major phenomena involving
context and memory, namely contextual cuing and source monitoring.
Memories bounded by contexts vary in their degree of insularity. A person
can be insensitive to interpretations of focal objects that involve inactive
contexts. The degree of insularity ranges from insular mental objects bound to
unique contexts, to completely decontextualized mental objects that need no
contextual referents. Decontextualized knowledge can be accessed and used
regardless of one’s currently instantiated context. Knowledge can become
decontextualized if it is retrieved and used in many varied contexts, because
such experience leads to the ability to access the material regardless of one’s
retrieval context. At the other extreme, strongly context-dependent memories
can be quite insular, i.e. inaccessible when context cues are not provided. This
insularity may be understood by analogy; context can play the analogous role
in human memory that is played by, for example, a carrier wave for a radio station.
Signals that are coded in relation to a reproducible reference, such as a carrier
wave, can only be recovered by reinstating the same referential information.
A radio program cannot be heard if one is tuned to the wrong station.
Likewise, contexts that differ from those that are encoded in association with
unique experiences cannot provide access to memories of those experiences.
Contextual fluctuation refers to the changes in one’s mental context with the
passage of time, shifting of environments, new stimuli and the flow of
consciousness. As time passes, the contents of one’s mental context tend to
change, as well. Thus, the relationship between clock time and contextual
fluctuation is probabilistic. Slow contextual fluctuation can occur within rigid,
unchanging mental states, and it is also possible for sudden shifts in one’s
mental context to occur when tasks, situations or environments are abruptly
changed.
113
20-Roediger-Chap20
114
11/16/06
5:00 PM
Page 114
CONTEXT AND HUMAN MEMORY
Other context-dependent memory phenomena include interference reduction effects (e.g. Bilodeau and Schlosberg 1951) and multiple-learning-context
effects (e.g. Smith et al. 1978). When two sets of materials are learned in different contexts, rather than both learned in the same context, an interference
reduction effect can be observed; recall of material learned in each context is
better because of less interference from the other set of materials. Another
reliable finding involving context and memory is that repeating to-be-learned
material in multiple contexts, relative to repetitions in a single context,
produces better retention, a multiple-learning-context effect. Interference
reduction and multiple-learning-context effects, both of which separate
learned material into different physical contexts, are the most robust effects to
be found in controlled laboratory studies of incidental environmental context
(Smith and Vela 2001). In both cases, the learning context acts as an organizational cue that subsequently can be used to facilitate recall of the learned
material. In interference reduction, the context cue is more specific to each set
of learned materials when each set has its own unique context cue; thus, when
recalling one set of materials, a context cue does not evoke material from the
potentially competing set of material. In multiple-learning-context effects,
learned material becomes bound to more context cues when multiple learning
contexts are used, resulting in more memory cues and, therefore, better recall.
The effects of context cues are relative, not absolute. The effects of context at
learning can be overshadowed by more potent, controlling influences, resulting
in the selective encoding of the more potent cues and a failure to encode
contextual material. One such source of potent noncontextual cues can be
semantic associations and relationships among to-be-remembered items.
Even if context has been successfully encoded, the effects of context at test can
also be nullified by the presence or use of more potent cues such as inter-item
semantic associations, an outshining effect. The degree to which focal experiences
mesh with one’s context can determine how much influence context has over
learning and remembering