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You Can't Take It with You: The Translation of Memory across DevelopmentAuthor(s): Rick Richardson and Harlene HayneSource: Current Directions in Psychological Science, Vol. 16, No. 4 (Aug., 2007), pp. 223-227Published by: Sage Publications, Inc. on behalf of Association for Psychological ScienceStable URL: http://www.jstor.org/stable/20183201 .
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CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE
You Can't Take It With You
The Translation of Memory Across Development Rick Richardson and Harlene Hayne
University of New South Wales, Sydney, Australia, and Otago University, Dunedin, New Zealand
ABSTRACT?Despite evidence for memory skill early in de
velopment, the evidence reviewed here shows that early
acquired memories, in rats and humans, are frozen in time.
That is, in the absence of opportunities for updating, early memories are
only expressed via responses or words that
were available at the time of encoding. We discuss the
theoretical importance of these findings and their potential clinical and forensic implications.
KEYWORDS?memory; development; fear; language
While there is substantial evidence that infants of many species are
capable of learning and remembering, developmental
changes in these processes may limit access to early memories
later in life. In humans, most adults have little or no recollection
of events that occurred prior to the age of 3 or 4 years, a phe
nomenon called infantile or childhood amnesia. Similarly, in a
wide range of altricial (i.e., requiring parental care for some
period of time after birth) nonhuman species, information that is
learned during infancy is not expressed in adulthood. Why might
this be?
There are a number of changes in memory processing that may
contribute to the inability to recall events that occurred early in
development (Hayne, 2004). Studies with both human infants
and infant rats have shown that younger organisms encode in
formation more slowly than their older counterparts do. Thus, for
any given learning experience, a younger organism establishes
a leaner representation (i.e., with fewer details) than an older
organism does. Furthermore, even when the level of encoding is
held constant across age groups, younger organisms forget faster.
These age-related changes in encoding and retention may help
to explain why adults show little or no retention of their early
experiences.
Age-related changes in memory expression may also play a
role in infantile amnesia (Pillemer & White, 1989). Although human infants learn and remember, their memories are pre
Address correspondence to Rick Richardson, School of Psychology,
University of New South Wales, Sydney 2052, Australia; e-mail:
r. richardson@unsw. edu. au.
sumably stored in a nonverbal format. As adults, most of our
memories are stored, retrieved, and expressed using language.
In order for memories encoded during infancy to be verbally
expressed, we would need to translate our preverbal represen
tation into language at some point during development. Fur
thermore, the neural basis of memory is different in infants
than it is in adults (e.g., Nelson, 1995; Seress, 2001). Memory
processing early in development is supported by one neural
substrate, while later in development it is supported by another.
If memories encoded during infancy are retained over significant
periods of development, they must be transferred from one
substrate to the other.
In this article, we review recent research designed to assess the
long-lasting effects of specific learning experiences that occurred
early in development. We try to answer two fundamental ques
tions. First, "Do we take our memories with us as we grow and
change?" Second, "If we do, does the expression of those mem
ories change during development?" We review research con
ducted with both infant rats and infant humans. Despite obvious
differences between these two species, conclusions regarding
memory development in both are remarkably similar.
MEMORY DEVELOPMENT IN RATS
Psychologists have long been interested in how fears are learned
and maintained, in part, because many anxiety disorders may be
due to specific learning experiences that occurred early in de
velopment (e.g., Jacobs & Nadel, 1985; Mineka & Zinbarg,
2006). Understanding the basic processes involved in memory
for fear-eliciting stimuli may lead to the development of effective
treatments for anxiety disorders. Research with nonhuman an
imals provides the opportunity to study the fate of a memory for a fearful experience across the entire lifespan, and rats are the
most common subjects in research of this kind. The initial
memory is typically established using Pavlovian fear condi
tioning; animals are presented with an innocuous conditioned
stimulus (CS; e.g., an odor or a tone) that is paired with an
aversive unconditioned stimulus (US; e.g., a shock). Subsequent
presentations of the CS elicit a variety of fear-like behaviors.
Some of the most frequently measured fear responses include
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Translation of Memory Across Development
freezing, changes in cardiovascular activity, and potentiated
startle responses to an unexpected, loud noise.
During development, behavioral indices of learned fear
emerge at different times. Specifically, freezing in response to a
CS previously paired with shock is observed at a younger age than are changes in heart rate, and changes in heart rate occur at
a younger age than potentiated startle (Hunt & Campbell, 1997). This sequential emergence of the behavioral components of
learned fear allows us to ask fundamental questions about the
translation and expression of memory across stages of develop
ment. Specifically, is learned fear expressed in a manner ap
propriate to the rat's age at the time of training or to its age at the
time of testing? If rats are trained at an age when they can ex
press learned fear via one response (e.g., freezing) but not some
other response (e.g., potentiated startle) and they are then tested
at a later age when they can express learned fear via both re
sponses, is the fear expressed through all the reactions available
to the animal at the time of test or is it expressed only by reactions
that were available at the time of training? When rats are trained on postnatal day (PND) 16 and tested
the following day, they exhibit freezing or avoidance to the
odor CS, but not a potentiated startle response to a loud, unex
pected noise in the presence of the CS. In contrast, rats trained
on PND22 and tested the following day exhibit freezing, avoid
ance, and potentiated startle in the presence of the CS. What
happens, however, when rats are trained on PND 16 and tested on
PND23? We have completed several studies that have explored this question (e.g., Richardson & Fan, 2002; Yap, Stapinski, &
Richardson, 2005). We have consistently found that rats do not
forget the CS-US association over the 1-week interval but that
they only express their learned fear via components of the fear
reaction that were available at the time of training. That is, they
freeze, but they do not exhibit potentiated startle (Fig. 1; see also, Barnet & Hunt, 2006). These results suggest that early-acquired
fear memories are not translated across development?at least
in terms of how they are
expressed?but are rather frozen in
time. In other words, early-acquired memories do not appear to
gain access to later-developing response systems. Although we
suspect that similar phenomena occur in other nonhuman
animals, to date, the issue has only been studied in rats.
MEMORY DEVELOPMENT IN CHILDREN
Although many of the basic memory processes exhibited by humans have been modelled in animals, our ability to encode,
retrieve, and express memories through language has no other
parallel in the animal kingdom. As adults, our receptive
language skills allow us to access memories very quickly;
sometimes only a few words are required to cue remarkably vivid
memories of past experiences, even when those experiences took
place a long time ago. Furthermore, our productive language
skills allow us to express our memories verbally, sharing
P16 P22 CS + US * test CS 24 hrs later CS + US * test CS 24 hrs later
Avoidance !2 Avoidance El Freezing S
Freezing 0 FPSS FPS0
P16 -? Test 1 week later *
P23
CS+US Avoidance E3
Freezing 0 FPS?
Fig. 1. Test of memory development in rats. Rats given pairings between a
conditioned stimulus (CS; in this case, an odor) and an unconditioned
stimulus (US; a shock) at 16 days of age (P16) express their learned fear of
the odor CS when they are tested 24 hours later through some behaviors
(e.g., avoidance, freezing) but not others (FPS; fear-potentiated startle). Rats trained at 22 days of age (P22) and tested 24 hours later express their
learned fear of the odor through all three behaviors. The critical finding is
that rats trained at 16 days of age and then tested at 23 days of age (P23) retain the odor-shock association across the 7-day interval, but they only
express their learned fear through response systems (i.e., avoidance and
freezing) that were mature at the time of training.
them with others who may or may not have shared our original
experience.
Although human infants exhibit rudimentary memory skills at
the time of birth and typically say their first word sometime around
their first birthday, their ability to use these two skills in concert
develops over a protracted period. Most children are fairly fluent
in their native language by about the age of four, but children this
age still have difficulty in verbally expressing their memories
(Simcock & Hayne, 2003). Given that the linguistic content of a
child's memory representation is likely to be very limited, verbal
recall of events that occurred during this period of development would require translation of the representation from a nonverbal to
a verbal format. Is there evidence that this occurs?
In our research, children participate in a unique experience
early in development, when their linguistic skill is extremely limited; they are then interviewed after a long delay, once their
language skills have improved. As in the infant-rat research
described earlier, we wondered whether children would express
their memory using all of the components available to them at the
time of the test (i.e., both verbal and nonverbal skills) or whether
their memory would be restricted to the components that were
available at the time of the original experience. The unique
experience is learning to operate a "Magic Shrinking Machine":
Two- to 4-year-old participants lift a lever, place a large object in
the machine, turn a handle, and retrieve a smaller but otherwise
identical object from a drawer at the front. (Shrinking is ac
complished by surreptitiously replacing the large object with a
smaller one.) After delays ranging from 1 day to 1 year, children's
verbal and nonverbal recall of the event is assessed (Simcock &
Hayne, 2002, 2003). During the verbal portion of the test, children are asked to describe what happened during the event;
during the nonverbal portion, they are asked to identify photo
graphs of the objects that were present and to reproduce the
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Rick Richardson and Marlene Hayne
actions required to operate the machine. Children's receptive
and productive language skills are measured at the time of the
original event and at the time of the test.
Children of all ages exhibit nonverbal memory for this event
even when tested after a 1-year delay. Furthermore, verbal recall
increases as a function of age and language skill. More impor
tantly, children's verbal recall after a delay reflects their vo
cabulary at the time of original encoding rather than their
vocabulary at the time of the test. Although their language skills
improve dramatically overtime (i.e., 6- or 12-months), children's
verbal reports at the test contain only event-relevant words that
were part of their vocabulary at the time of the original event.
In no instance has a child in our research used a word or words
that were not part of his/her productive vocabulary at the time
of encoding. Thus, even though children's language skills
have improved over the delay and they have maintained non
verbal representations of the event, they do not map their new
language skills onto their existing memory representations
(see Fig. 2). In other words, children do not simply retrieve their
nonverbal representations of the event and tell verbal stories
about it. This same basic finding has been reported in other
studies in which children have been interviewed about more
emotional events, including trips to the emergency room (Howe,
Courage, & Peterson, 1994). These studies have also shown that
it is difficult (Cheatham & Bauer, 2005), if not impossible, for
children to map their new language skills onto their existing
nonverbal memory representations.
UPDATING OF EARLY MEMORIES
In the research described so far, participants are exposed to a
discrete event for a very brief period (e.g., a few minutes), and
they do not experience anything similar to that event during the
retention interval. While some early experiences may share
these characteristics, others would not. Some experiences may
occur over and over again. What happens to early memories if
the target event, or something similar, occurs repeatedly? Is the
original memory updated to reflect current environmental con
ditions or response patterns? Although we don't know for sure,
some of our recent research (Yap et al., 2005) suggests that such
updating may occur. For example, if rats are trained to fear one
odor at PND16 and then trained to fear a second, discriminably different odor at PND22, they express their fear of the first odor
via the potentiated startle response when tested at PND23. In
other words, these rats express their fear to the earlier-trained
CS by a response that has matured during the retention interval
(also see Barnet & Hunt, 2006). This result suggests that earlier
acquired nonverbal memories can be updated if they are
reactivated and re-encoded at later stages of development (see
Hartshorn & Rovee-Collier, 2003). Evidence regarding verbal updating of preverbal memories is
much more equivocal. For example, Peterson and Rideout
(1998) repeatedly interviewed children about a medical injury
they had suffered over a period of 18 to 24 months. At the time of
the injury, children ranged in age from 12 to 34 months. Older
children reported more information than younger children did
and the amount of information reported increased across
successive interviews. Importantly, although the youngest par
ticipants did not provide verbal accounts of their injuries at the
time that they happened, they did provide verbal accounts when
interviewed after a delay. Although it is possible that the
youngest participants translated their preverbal representations
into language as their language skills improved, it is also pos sible that, over time, children incorporated more of what they
had been told by others about the events into their own accounts.
That is, during the later interviews, children's reports may have
been updated and augmented to include other sources of infor
mation that they had encountered after their memories were
originally established. In this way, children's reports of their
earlier experiences would be based in part on their own episodic
memories for the events, but would also include secondhand
information that others had told them. We assume that children's
memories could be updated in a similar way by exposure to
photos or videos of the original event. In this case, what children
ultimately report may include information that was encoded
at the time the event took place as well as information that was
encoded on the basis of exposure to photos or video.
IMPLICATIONS
What are the implications of the data reviewed here? We propose
that, unless they are "updated," memories for discrete events that
occur very early in life are not translated across stages of devel
opment. Rather, these memories, if retained, are maintained in
the same representational format in which they were originally encoded. Therefore, these early memories are
expressed in a
manner quite different from the way in which they would be
expressed if acquired later in development. If we are correct,
the data outlined here have important implications in both clinical
and forensic contexts. From a clinical perspective, we would
predict that fears, phobias, and anxiety in adults that are due
to early discrete trauma may be expressed in a manner that is
more similar to the way in which young organisms express
their fear. We know that early-acquired memory representations
are leaner than memories acquired later in development, and
might therefore generalize more broadly (e.g., Jacobs & Nadel,
1985). Extrapolating from research with infants and children, we would also predict that individuals are unlikely to gain full,
explicit recollection of the original trauma. Given this, psycho
logical difficulties that originate from these kinds of early expe riences may be particularly difficult to treat because their effects
become entrenched in an individual's behavior and personality,
even though the fear-eliciting events cannot be recalled or
discussed.
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Translation of Memory Across Development
Nonverbal
Memory
Representation
B Language
Acquisition
2 45 o o CO 40
| 35 -Q S^ 30 o
> cd 25
?o 20 CD
Q. X LU
15'
Retention Interval
Photo Reenactment
Nonverbal Memory Measure
23
22
Li Encoding Test
Assessment
10
co 21
o 20
S 19 CD E? 18 03
r- 17
16
15' L_J?L Encoding Test
Assessment
CD
c5 r
2
0 Photo Reenactment Verbal
Memory Measure
Fig. 2. Test of memory development in small children. Two-year-old children established a nonverbal memory representation (A; tested
through photo recognition and behavioral reenactment) of the magic shrinking machine and maintained some of that representation over a 1
year delay (top graph). Children's general language skills (Expressive Vocabulary) and their task-specific vocabulary (Target Words) increased
over that time period (B); by the time of the 1-year test, children had acquired most of the words that were required to describe the magic
shrinking machine. Despite this, children failed to map their new language skills onto their nonverbal representation of the target event (C).
Although at the 1-year test children recognized photographs (Photo) and performed actions (Reenactment) that had not been part of their
productive vocabulary at the time of original encoding, in no instance did a child use a word or words that had not been part of their productive
vocabulary at the time of original encoding to describe the event 1 year later.
From a forensic perspective, although traumatic events that
take place during early development undoubtedly leave their
mark, the finding that children do not readily translate their
early memories into language limits the probability that an in
dividual abused as an infant or very young child could provide a coherent verbal account of those experiences several years
later, particularly if the events have not been discussed in the
meantime (Hayne, 2006). Finally, from a developmental per
spective, the data reviewed here provide new clues to the age-old
mystery of childhood amnesia. We hypothesize that one reason
we do not recall much of our infancy and early childhood may be
that those memories were encoded in a fundamentally different
format. Because many of our early experiences are never re
peated, our memories for them are not retrieved or updated,
and these memories get left behind on our journey across
development.
Acknowledgments?This work was supported by Australian
Research Council Discovery grants to Rick Richardson
(DP0346139, DP0666953) and by a Marsden grant (UOO096) from the Royal Society of New Zealand to Harlene Hayne.
Recommended Reading
Barnet, R.C., & Hunt, P.S. (2006). (See References)
Hayne, H. (2006). (See References)
Yap, C.S.L., Stapinski, L., & Richardson, R. (2005). (See References)
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Rick Richardson and Marlene Hayne
REFERENCES
Barnet, R.C., & Hunt, P.S. (2006). The expression of fear-potentiated startle during development: Integration of learning and response
systems. Behavioral Neuroscience, 120, 861-872.
Cheatham, C.L., & Bauer, P.J. (2005). Construction of a more coherent
story: Prior verbal recall predicts later verbal accessibility of early memories. Memory, 13, 516-532.
Hartshorn, K., & Rovee-Collier, C. (2003). Does infant memory ex
pression reflect age at encoding or age at retrieval? Developmental
Psychobiology, 42, 283-291.
Hayne, H. (2004). Infant memory development: Implications for
childhood amnesia. Developmental Review, 24, 33-73.
Hayne, H. (2006). Verbal recall of preverbal memories. In M. Garry &
H. Hayne (Eds.), Do justice and let the sky fall: Elizabeth Loftus and
her contributions to science, law, and academic freedom (79-103).
Hillsdale, NJ: Erlbaum.
Howe, M.L., Courage, M.L., & Peterson, C. (1994). How can I remember
when "I" wasn't there? Long-term retention of traumatic memories
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Hunt, P., & Campbell, B.A. (1997). Developmental dissociation of the
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Jacobs, W.J., & Nadel, L. (1985). Stress-induced recovery of fears and
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Mineka, S., & Zinbarg, R. (2006). A contemporary learning theory
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Nelson, C.A. (1995). The ontogeny of human memory: A cognitive neu
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ademic Press.
Richardson, R., & Fan, M. (2002). Behavioral expression of conditioned
fear in rats is appropriate to their age at training, not their age at
testing. Animal Learning & Behavior, 30, 394-404.
Seress, L. (2001). Morphological changes of the human hippocampal formation from midgestation to early childhood. In C.A. Nelson
& M. Luciana (Eds.), Handbook of developmental cognitive neuroscience (pp. 45-58). Cambridge, MA: MIT Press.
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