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Title
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Implicit Memory
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Author
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McBride, Dawn M.
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Research Area
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Cognition and Emotions
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Topic
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Memory
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Abstract
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Implicit memory involves the influence of memory without intention and often without awareness. For example, many of the tasks we perform without conscious control are considered implicit tasks. These include tasks with which we have experience such as riding a bicycle, driving a car, or typing. In this essay, the study of implicit memory is briefly reviewed beginning with discussion of foundational studies in this area that followed either a processing or memory systems perspective on this topic. Some current, cutting edge research is reviewed with primary emphasis on questions that hold promise for new knowledge about implicit forms of memory: (i) In what ways is conceptual implicit memory (memory without intention) similar to explicit memory (memory with intention)? (ii) What roles do item‐specific (focus on details of an item) and relational (focus on connections between items) processing play in implicit memory retrieval? (iii) What is the role of attention in implicit memory retrieval? Examination of these questions provides avenues for future research in this area.
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Identifier
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etrds0178
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extracted text
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Implicit Memory
DAWN M. McBRIDE
Abstract
Implicit memory involves the influence of memory without intention and often without awareness. For example, many of the tasks we perform without conscious control
are considered implicit tasks. These include tasks with which we have experience
such as riding a bicycle, driving a car, or typing. In this essay, the study of implicit
memory is briefly reviewed beginning with discussion of foundational studies in
this area that followed either a processing or memory systems perspective on this
topic. Some current, cutting edge research is reviewed with primary emphasis on
questions that hold promise for new knowledge about implicit forms of memory: (i)
In what ways is conceptual implicit memory (memory without intention) similar to
explicit memory (memory with intention)? (ii) What roles do item-specific (focus on
details of an item) and relational (focus on connections between items) processing
play in implicit memory retrieval? (iii) What is the role of attention in implicit memory retrieval? Examination of these questions provides avenues for future research
in this area.
INTRODUCTION
Implicit forms of memory have interested researchers for the past several
decades. While the majority of research in memory has focused, and still
does focus, on explicit forms of memory (i.e., conscious and intentional
retrieval of previously studied information), the number of studies examining implicit forms of memory has greatly increased over the past 40
years or so. Unlike explicit tests of memory, implicit tests are those that
access memories of our experiences without intentional retrieval of those
experiences. In other words, implicit memory is used in situations where
our memory influences our behavior without our intention for it to do so.
For example, when we improve on a skill with practice (e.g., making a free
throw), we access memory for that skill each time we perform it, but we do
not need to explicitly remember performing the skill in the past in order
to practice the skill. In many laboratory implicit tests, implicit memory
is shown by facilitation of responses to items previously studied without
intentional retrieval of the information. Typical implicit tasks show greater
Emerging Trends in the Social and Behavioral Sciences. Edited by Robert Scott and Stephen Kosslyn.
© 2015 John Wiley & Sons, Inc. ISBN 978-1-118-90077-2.
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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES
or faster responses to test items corresponding to studied items compared
with items on the test that do not correspond to studied items. For example,
after previously studying words, subjects are faster to identify those items
as words in a lexical decision task compared with words that have not
been studied. Completion rates of word fragments or stems with studied
items are also higher compared with items that have not been studied when
subjects are asked to complete cues with the first word they think of. For
more descriptions of typical implicit memory tests, see reviews by Roediger
and McDermott (1993) and Schacter (1987).
FOUNDATIONAL RESEARCH
The surge in interest in implicit memory was precipitated in large part by
studies conducted by Warrington and Weiskrantz (1968, 1970, 1974). In these
studies it was shown that although amnesic patients have decremented
performance on typical explicit memory tests such as recognition (i.e., discriminate between studied and unstudied items) and recall (i.e., generation
of information from memory), their performance on an implicit memory
test (e.g., stem completion) does not differ from nonamnesic patients. These
results indicate that not only can performance on explicit and implicit
tests can be dissociated, but that the dissociation may have a neurological
basis. These conclusions led to lines of research examining performance in
implicit tests in nonpatient populations and further investigations of the
neurological basis of explicit/implicit test differences. I will briefly review
key findings in each of these lines of work below.
Research with nonpatient populations has revealed some interesting
aspects of implicit memory that distinguish it from explicit forms of memory. For example, Jacoby and Dallas (1981) showed that implicit memory
tested with a perceptual identification task (i.e., subjects are asked to identify
words that are flashed on the screen for very brief intervals) is not affected
by depth of processing manipulations that typically affect explicit memory.
Srinivas and Roediger (1990) also reported a dissociation between implicit
and explicit tests based on whether words are simply read or are generated
from an associative cue during the study phase. In their study, an explicit
test of free recall resulted in better memory for studied words when words
had been generated than when they had been read at study, but an implicit
test of word fragment completion resulted in better memory for studied
words when words had been read than when they had been generated at
study (see also Jacoby, 1983). Finally, Roediger and Blaxton (1987) showed
that implicit memory for words was higher on a word fragment completion
test when the same font (hand-printed or typed) was used at study and
test than when the font was changed from study to test. Taken together,
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these studies (and many others like these—see Schacter, 1992) suggested
that unlike explicit memory, implicit memory relies more on perceptual (i.e.,
surface features) processing than on semantic (i.e., meaning) processing.
In 1990, however, Roediger described results from different kinds of
implicit tests that could be dissociated with study processing manipulations
(meaning-based semantic processing versus surface feature-based perceptual processing). Roediger proposed that two key classification categories
of implicit tests should be considered: implicit tests relying on perceptual
processing such as perceptual identification and fragment completion
tasks and implicit tests relying on semantic processing such as category
production and verification tasks. Unlike perceptual implicit tests, semantic
implicit tests are affected more often by semantic encoding manipulations
like depth of processing than by perceptual encoding manipulations. He
suggested that a transfer-appropriate processing (i.e., a match in processing
type for study and test results in better memory for information) perspective
(see Morris, Bransford, & Franks, 1977) on these tests revealed a different
classification of tests where type of processing was more important than
whether the retrieval was intentional or not.
In contrast to this processing approach, researchers who focused more
on the neurological aspects of implicit and explicit memory differences
suggested that implicit and explicit memory differences are because of the
reliance on separate memory systems (see the brief review by Squire, 2004).
Driven by studies showing that amnesic patients with damage to the hippocampus and related brain structures in the medial temporal lobes show
decrements in explicit but not implicit memory tests, neuropsychologists
began to explore the brain areas responsible for performance on implicit tests
that were intact in such patients. These studies have shown that neocortical
areas are involved in completion of implicit tests (see Schacter, Chiu, &
Oschner, 1993, for a review). In 1994, a seminal work from the systems
perspective was published in the form of a book titled Memory Systems
1994. In this book, authors proposed various memory systems responsible
for implicit and explicit memory based on neurological and psychological
studies that preceded it.
A final key publication that focused on how researchers should be
measuring implicit and explicit forms of memory should be discussed as
foundational in the study of implicit memory. Jacoby (1991) proposed that
researchers should not be equating performance on implicit and explicit
memory tests with the processes underlying the tests, as these tests typically
involve a mixture of processes. As an alternative to assuming that explicit
memory tests measure intentional, conscious forms of memory and that
implicit memory tests measure automatic, unconscious forms of memory,
Jacoby proposed a process dissociation procedure to allow for measurement
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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES
of the processes underlying these tasks. His procedure estimates conscious
(i.e., intentional) and automatic (i.e., unintentional) memory processes
through the use of an exclusion task that sets conscious and automatic
processes as opponent processes in completion of the task. In the exclusion
task, subjects are to exclude items they consciously recollect as studied.
Given these instructions, responses that match studied items are assumed
to rely on automatic memory. The process dissociation procedure relies on
an assumption of independence between conscious and automatic memory,
which has been criticized (see Curran & Hintzman, 1995; Hintzman &
Curran, 1997, and response by Jacoby & Shrout, 1997), but this procedure
has been highly influential in work in implicit memory (see Yonelinas &
Jacoby, 2012, for a recent review) and in other areas of psychology as a
method of estimating underlying conscious and automatic processing in
different cognitive tasks (e.g., in judgment and decision making, see Ferreira,
Garcia-Marques, Sherman, & Sherman, 2006). Jacoby’s process dissociation
procedure has also led to the development of more complex models of
implicit and explicit memory tasks with a goal of estimating the conscious
and automatic processes that underlie these tasks (see McBride, 2007, for a
review of estimation techniques).
CUTTING EDGE RESEARCH
In the past decade, research in implicit memory has slowed. Fewer memory
studies have focused on these types of tests than in the preceding three
decades. However, some notable studies have taken the field of implicit
memory in new directions. One area of exploration has considered the
connection between embodied cognition (i.e., the idea that cognition arises
from bodily interaction with the world) and implicit memory. In his paper
that discussed what memory is for, Glenberg (1997) suggested a contribution
of embodiment to unintentional forms of memory such as implicit memory.
Recently, Topolinski (2012) examined these ideas in a study that showed
that motor movements specific to the target stimuli affect implicit memory.
Subjects were asked to perform motor tasks that were in the same (oral) or
different (manual) modality as the study stimuli (words). Performing the
motor task of the same modality during study reduced implicit memory in
fragment completion tasks. This study represents a unique perspective on
implicit memory and has the potential to yield new knowledge in this area.
Another recent perspective on implicit memory suggests that implicit and
explicit tasks should not be categorized according to whether or not consciousness is needed for the task, but rather if the task involves the formation
of a new association between concepts. Reder, Park, and Kieffaber (2009) proposed that the mainstream view of distinct memory systems for explicit and
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implicit forms of memory does not accurately represent the brain systems
that are involved in memory tasks. They reviewed the evidence for the memory systems view of implicit and explicit memory and showed that much of
this evidence is inconsistent. They proposed instead that implicit and explicit
memory tasks access the same representations of concepts and described an
activation model of processing in these tasks that can explain many of the dissociations that have been relied on as evidence for distinct systems. This new
perspective can lead researchers in new directions in the study of implicit
memory that do not rely on traditional classifications of tasks (see Erdelyi,
2010, for a similar argument).
KEY ISSUES FOR FUTURE RESEARCH
Simply because research in implicit memory has slowed is by no means an
indication that we have answered many of the open questions regarding
these tests. Some key questions that future research will address are: (i) In
what ways is conceptual (i.e., meaning-based) implicit memory similar to
explicit memory? (ii) What roles do item-specific (i.e., focus on details of
information) and relational (i.e., focus on connections between information)
processing play in implicit memory retrieval? and (iii) What is the role of
attention in implicit memory retrieval? Each of these questions is being
explored by current research in implicit memory.
CONCEPTUAL IMPLICIT AND EXPLICIT MEMORY
Owing to findings showing similar effects of semantic and attention
manipulations on both conceptual implicit memory and explicit memory,
researchers have suggested that these forms of memory may be similar
and/or are controlled by the same areas of the brain. For example, Yonelinas
et al. (e.g., Diana, Yonelinas, & Ranganath, 2007; Wang, Lazzara, Ranganath,
Knight, & Yonelinas, 2010; Yonelinas, Aly, Wang, & Koen, 2010) have
shown that both recognition familiarity (see Yonelinas, 2002, for a review
of processes involved in explicit recognition tests) and conceptual implicit
memory are connected to activity in the perirhinal cortex. Further, Wang and
Yonelinas (2012) recently reported results indicating correlations between
recognition familiarity and conceptual implicit memory, supporting past
studies showing similarities between these two forms of memory (e.g.,
Wagner & Gabrieli, 1998). Wang and Yonelinas concluded that “it is likely
that the cognitive process that supports familiarity judgments also supports
conceptual implicit memory” (p. 1161). However, some limitations to testing
this hypothesis exist. As described above, there are multiple methods of
measuring implicit memory processes, and there are also multiple methods
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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES
for measuring recognition familiarity (see Yonelinas, 2002). Thus, it is unclear
how much the support for this hypothesis depends on the specific process
measurement techniques employed by researchers. Further, recognition
and conceptual implicit memory tests require different decision processes
making it likely that familiarity and conceptual implicit memory do not
completely overlap. In fact, Wang and Yonelinas reported that in one of
their experiments, familiarity only accounted for 22% of the variance in
conceptual implicit memory. Thus, researchers will need to circumvent such
issues in their exploration of this question.
ITEM-SPECIFIC AND RELATIONAL PROCESSING IN IMPLICIT MEMORY
The item-specific/relational processing (Humphreys, 1976) distinction has
been a focus of numerous research studies in memory in the past few
decades. Item-specific processing involves processing features unique to
an item, whereas relational processing involves processing of the common
features across items. It appears to be an important distinction in explaining
distinctiveness effects in explicit memory (see Hunt, 2006, 2012) and recently
has been investigated in implicit memory tests. Mulligan (2006) suggested
that the item-specific/relational processing distinction explains some dissociations across implicit and explicit tests. He points to differences across
implicit and explicit tests as responsible for dissociations found between
these tests. Explicit memory tests such as free and cued recall are thought to
rely on both relational and item-specific processing: Relational processing
aids in the generation of items for response and item-specific processing
aids in distinguishing studied from unstudied items. Because there is no
need to distinguish between studied and unstudied items in conceptual
implicit tests, there is no need to rely on item-specific processing. However,
item generation for responses is still important; thus, relational processing
is important in these tests. Mulligan (2012) recently showed that conceptual
implicit and explicit tests can be doubly dissociated when different category
sizes of studied items changed the amount of item-specific and relational
processing needed to complete the test. Results supported the idea that
relational processing was important for the conceptual implicit test, but
a condition that emphasized item-specific processing resulted in better
memory in the conceptual explicit test. Parker, Dagnall, and Munley (2012)
supported these ideas in a recent study as well.
An important limitation in exploring this question is that conceptual
implicit tests are more susceptible to explicit retrieval contamination (i.e.,
intentional retrieval of an experience despite instructions for the task that
do not connect to previous experiences), making it difficult to interpret
the results from some studies employing these tasks (see Jacoby’s, 1991,
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argument against equating tasks with processes described above). Thus,
it may be important for future studies to include multiple measurement
methods to provide converging evidence for the relative importance of
item-specific and relational processing in implicit memory tests.
ATTENTION AND IMPLICIT MEMORY
Mulligan (e.g., Mulligan & Hartman, 1996) has also explored the role of
attention in implicit memory tests. Past research has shown that like explicit
memory, conceptual implicit memory is affected by dividing attention.
However, perceptual implicit memory tests are not typically affected by
manipulations of attention. In more recent studies, Lozito and Mulligan
(2010) and Spataro, Cestari and Rossi-Arnaud (2011) explored effects of
attention on implicit memory. Spataro et al. conducted a meta-analysis of
studies that examined effects of manipulations of attention at encoding in
implicit memory tests. They found a small effect of attention manipulations
in both perceptual and conceptual implicit tests with greater effects in
production than identification implicit tests. Lozito and Mulligan examined
the effect of dividing attention at retrieval in implicit tests and found no
difference between divided and full attention conditions in the implicit tests.
In addition to some of the limitations raised for the first two questions
above, examinations of attention effects in implicit tests must address the
issue of the degree to which the manipulations affect attention. Different
tasks can tax attentional resources to varying degrees and when no effects
of attentional manipulations are found, results may be because of the use
of tasks that require fewer cognitive resources. Thus, evidence from studies that include different attentional manipulation tasks is needed to provide
converging evidence for such findings.
SUMMARY
Much has been learned in the past several decades about implicit memory
and how it is similar to and different from explicit memory. However, the
three questions described above regarding the similarity of conceptual
implicit and explicit memory, the role of item-specific and relational processing in implicit tests, and the role of attention in implicit tests are some
of the questions researchers are currently attempting to answer to gain
further understanding about the processing involved in implicit memory.
The examination of these questions and the unique perspectives on research
in implicit memory reviewed in the two sections above hold promise in the
attainment of new knowledge in this field of study.
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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES
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FURTHER READING
Jacoby, L. L. (1991). A process dissociation framework: Separating automatic from
intentional uses of memory. Journal of Memory and Language, 30, 513–541.
McBride, D. M. (2007). Methods for measuring conscious and automatic memory: A
brief review. Journal of Consciousness Studies, 14, 198–215.
Reder, L. M., Park, H., & Kieffaber, P. D. (2009). Memory systems do not divide on
consciousness: Reinterpreting memory in terms of activation and binding. Psychological Bulletin, 135, 23–39.
Roediger, H. L., III, & McDermott, K. B. (1993). Implicit memory in normal human
subjects. In J. Grafman & F. Boller (Eds.), Handbook of neuropsychology (Vol. 8, pp.
63–131). Amsterdam, The Netherlands: Elsevier.
Schacter, D. L., & Tulving, E. (1994). Memory systems 1994. Cambridge, MA: MIT
Press.
Yonelinas, A. P., & Jacoby, L. L. (2012). The process-dissociation approach two
decades later: Convergence, boundary conditions, and new directions. Memory &
Cognition, 40, 663–680.
DAWN M. McBRIDE SHORT BIOGRAPHY
Dawn M. McBride is a Professor of Psychology at Illinois State University.
Her research includes work in implicit memory, false memory, forgetting,
and prospective memory. She is the author of a number of journal articles in
these areas and the introductory methods textbook The Process of Research in
Psychology. She also coedited the book The Concepts of Consciousness: Integrating an Emerging Science with J. Scott Jordan. More information can be found
at: http://about.illinoisstate.edu/dmmcbri
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