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THE ENACTMENT EFFECT
STUDIES OF A MEMORY PHENOMENON
by
Lars Nyberg
rr,
1993
THE ENACTMENT EFFECT
STUDIES OF A MEMORY PHENOMENON
Lars Nyberg
Doctoral dissertation to be publicly discussed in lecture room S2,
at the Department of Psychology, University of Umeå, on April 23, 1993,
at 10.15 a.m., for the degree of Doctor of Philosophy.
1993
UNIVERSITY OF UMEÅ
Department of Psychology
DOCTORAL DISSERTATION
April, 1993
Author: Nyberg, L.
Title: The enactment effect: Studies of a memory phenomenon.
Abstract
The enactm ent effect refers to the superior memory performance of
enacted events over nonenacted events. There has been considerable
disagreement on how to explain this effect, and it has been claimed th a t
the basic laws of enacted and nonenacted events are different. The present
thesis addressed both of these aspects of memory for enacted events. In
Study I (Nilsson, Cohen, & Nyberg, 1989), the slopes of the forgetting
curves for enacted and nonenacted events were compared, and found to be
similar. In Study II (Nyberg, Nilsson, & Bäckman, 1992), the effect of age
on recall of enacted and nonenacted events was studied, and an aging
effect was found for both types of events. In Study III (Nyberg, Nilsson, &
Bäckman, 1991), it was attem pted to sort out various components
contributing to the enactment effect, but no single component was found to
be a prerequisite for the effect. Study IV (Nyberg & Nilsson, 1992) tested
the hypothesis stating th a t conceptual inform ation is contributed by
enacted events. No support was found for this hypothesis. Based on the
results of Study I and II, and a critical review of the literature, it is
concluded th a t there is no reason for introducing new laws of memory for
enacted events. The results of Study III and IV are discussed in relation
to contemporary accounts of the enactment effect, and several features of
previous explanations of the effect are called into question. Finally, a
tentative model is proposed in which the enactment effect is explained in
terms of enactment increasing the distinctiveness of the memory traces by
adding item-specific and relational information.
Key words: Memory, enactm ent, memory laws, memory trace, itemspecific information, relational information, distinctiveness.
I: Nilsson, L.-G., Cohen. R. L., & Nyberg, L. (1989). Recall of enacted and
nonenacted instructions compared: Forgetting functions. Psychological
Research, 51,188-193.
II: Nyberg, L., Nilsson, L.-G., & Bäckman, L. (1992). Recall of actions,
sentences, and nouns: Influences of adult age and passage of time. Acta
Psychologica, 79, 1-10.
Ill: Nyberg, L., Nilsson, L.-G., & Bäckman, L. (1991). A component
analysis of action events. Psychological Research, 53, 219-225.
IV: Nyberg, L., & Nilsson, L.-G. (1992). The role of enactment on implicit
and explicit memory. Manuscript submitted for publication.
Number of pages: 45; ISBN 91-7174-774-5
THE ENACTMENT EFFECT
STUDIES OF A MEMORY PHENOMENON
Lars Nyberg
Abstract
Nyberg, L. The enactment effect: Studies of a memory phenomenon. Doctoral
Dissertation, Department of Psychology, University of Umeå, S-902 47 Umeå, Sweden,
1993; ISBN 91-7174-774-5.
The enactm ent effect refers to the superior memory performance of
enacted events over nonenacted events. There has been considerable
disagreement on how to explain this effect, and it has been claimed th a t
the basic laws of enacted and nonenacted events are different. The present
thesis addressed both of these aspects of memory for enacted events. In
Study I (Nilsson, Cohen, & Nyberg, 1989), the slopes of the forgetting
curves for enacted and nonenacted events were compared, and found to be
similar. In Study II (Nyberg, Nilsson, & Bäckman, 1992), the effect of age
on recall of enacted and nonenacted events was studied, and an aging
effect was found for both types of events. In Study III (Nyberg, Nilsson, &
Bäckman, 1991), it was attem pted to sort out various components
contributing to the enactment effect, but no single component was found to
be a prerequisite for the effect. Study IV (Nyberg & Nilsson, 1992) tested
the hypothesis stating th a t conceptual inform ation is contributed by
enacted events. No support was found for this hypothesis. Based on the
results of Study I and II, and a critical review of the literature, it is
concluded th a t there is no reason for introducing new laws of memory for
enacted events. The results of Study III and IV are discussed in relation
to contemporary accounts of the enactment effect, and several features of
previous explanations of the effect are called into question. Finally, a
tentative model is proposed in which the enactment effect is explained in
term s of enactment increasing the distinctiveness of the memory traces by
adding item-specific and relational information.
K ey w.ords: Memory, enactm ent, memory laws, memory trace, itemspecific information, relational information, distinctiveness.
Lars Nyberg
Number of pages: 45; ISBN 91-7174-774-5.
Preface
The present doctoral dissertation is based on the following papers:
I: Nilsson, L.-G., Cohen. R. L., & Nyberg, L. (1989). Recall of enacted and
nonenacted instructions compared: Forgetting functions. Psychological
Research, 51,188-193.
II: Nyberg, L., Nilsson, L.-G., & Bäckman, L. (1992). Recall of actions,
sentences, and nouns: Influences of adult age and passage of time. Acta
Psychologica, 79, 1-10.
Ill: Nyberg, L., Nilsson, L.-G., & Bäckman, L. (1991). A component
analysis of action events. Psychological Research, 53, 219-225.
IV: Nyberg, L., & Nilsson, L.-G. (1992). The role of enactment on implicit
and explicit memory. Manuscript submitted for publication.
This research was supported by grants from The B ank of Sweden
Tercentary Foundation to Lars-Göran Nilsson and Lars Bäckman, and
from The Swedish Council for Research in the Humanities and the Social
Sciences to Lars-Göran Nilsson.
Acknowledgements
Many persons have, directly or indirectly, supported me throughout my
Ph. D. studies, and helped me completing this dissertation. Thanks to:
My supervisor, Lars-Göran Nilsson. Lars-G öran's im portance for the
completion of this dissertation can not be overestimated. From the start of
my graduate studies he has trusted me a large portion of independence in
my work. At the same time, whenever consulted he has offered the best
possible guidance. To me, this form of supervision has been optimal.
My room mate, Ulrich Olofsson. Our many discussions have sharpened
my thinking and made the work at the department a lot more enjoyable.
My lunch partner, Bo Molander. Bo has always been willing to help me
with various m atters related to statistics, psychology, and genealogy.
My co-authors, Lars Bäckman and Ronald Cohen. It has been a privilege
to work with these two experts on action memory.
My colleagues a t the D epartm ent of Psychology in Umeå. It has always
been a pleasure to go to the department. This is largely due to the friendly
atmosphere prevailing in classes, in seminars, in the research group on
memory, and in the coffee room.
My p aren ts, Stig and Laila. They have provided w hole-hearted
encouragement throughout my education.
Finally, my girlfriend Erica Edström. Erica has assisted me in my work
by being pilot subject, helping me to find subjects, and by commenting on
papers, posters, and talks. But more importantly, she has given me most
effective retrieval cues to help me remember th a t there are a few other
things in life than science.
March, 1993
Lars 9{y6erg
Contents
Introduction
1
Memory of enacted events
3
Separate laws for memory of enacted and nonenacted events
5
Theoretical explanations of the enactment effect
10
Overview of the empirical studies
15
Study I (Nilsson, Cohen, & Nyberg, 1989)
15
Study II (Nyberg, Nilsson, & Bäckman, 1992)
16
Study III (Nyberg, Nilsson, & Bäckman, 1991)
17
Study TV (Nyberg & Nilsson, 1992)
19
General discussion
21
Memory laws
22
Theoretical explanations
25
A distinctiveness model
28
Concluding rem arks
33
References
34
v
Introduction
MEMORY is the name given to the process of encoding, storage, and
retrieval of information (Murdock, 1974; Tulving, 1987). Traditionally,
memory has been viewed as an unitary entity, but during recent years
there has been a shift in orientation. Today, a lot of research is devoted to
the question of whether memory really is unitary, or consists of several
interrelated brain systems. A number of different classificatory schemes
have been proposed by proponents of a multiple memory systems view (for
a review, see Tulving, 1985). In order to define the domain of the present
thesis, I will briefly describe one influential organizational scheme
suggested by Tulving and Schacter (1990). This scherno distinguishes
between four long-term memory systems: Procedural memory is believed
to underlie changes in skillful performance and responding to stimuli;
prim ing is concerned with identification of perceptual objects; semantic
memory is concerned with acquisition and use of factual knowledge; and
episodic memory mediates memory of personally experienced events. The
present thesis is concerned with a phenomenon of episodic memory.
Tulving (1979) suggested an orientation toward phenomena of episodic
memory in which recollection of an event is jointly determined by the
inform ation stored in memory about the event (the trac e1) and the
information th a t is available to the rememberer at retrieval (the cue).
Successful recollection is dependent on the compatibility between trace
and cue information, a dependency which is salient in the encoding
specificity hypothesis (Thomson & Tulving, 1970). To this hypothesis was
later on added the encoding specificity principle (Tulving & Thomson,
1973). This principle states th a t "specific encoding operations performed
on w hat is perceived determ ine w hat is stored, and w hat is stored
determines what retrieval cues are effective in providing access to what is
stored" (Tulving & Thomson, 1973, p. 369). The form ulation of the
principle made the dependence of the memory trace on the encoding
op erations m ore explicit. This inter-d ep en d en cy betw een th e
characteristics of memory traces and the encoding operations performed
1 Several different views on traces have been put forward in the literature (e.g., vectors,
lists, nodes, points, see Estes, 1991). At this point, the term "trace” is used, without any
commitment as to its nature, to refer to a persistent change in the memory system
following perception of an episodic event (Craik, 1979).
1
at input has been considered in explanations of the effect of several
encoding manipulations:
The concept of encoding elaboration was introduced by Craik and Tulving
(1975). They showed th at encoding manipulations th at served to elaborate
or enrich the encoded trace of a targ et word led to better memory
performance; memory performance was seen as dependent on the
elaboratness of the final encoding. In explaining how elaboration
improves performance, the concept of elaboration has been tied to the
concept of distinctiveness of the memory trace (Jacoby & Craik, 1979;
Lockhart & Craik, 1990; Moscovitch & Craik, 1976). Elaborative processing
a t encoding is believed to allow form ation of a more distinctive,
discrim inable memory trace th a t stands out and is therefore more
retrievable.
Degree of rehearsal has for a long time been associated with degree of
memory performance (e.g., Rundus, 1971). Craik and Lockhart (1972)
suggested th a t rehearsal can be broken down into two m ain types;
m a in te n a n c e rehearsal and e la b o ra tive reh ea rsal. M aintenance
rehearsal involves m aintained processing a t the same level of analysis,
w hereas elaborative reh earsal leads to fu rth er elaboration of the
stim ulus. The original assum ption was th a t only the la tte r form of
rehearsal produced improved memory performance (Craik & Lockhart,
1972). This assumption, based on the hypothesis th a t only elaborative
rehearsal causes perm anent changes in the memory trace, received some
experimental support (e.g., Craik & Watkins, 1973). However, it was also
shown th a t recognition memory clearly benefits from m aintenance
rehearsal (Woodward, Bjork, & Jongeward, 1973), and the current view is
th a t m aintenance rehearsal produces small increases in recall, and
substantial increases in recognition (Greene, 1987). Clearly, this shows
th a t also maintenance rehearsal can produce perm anent changes in the
memory trace, although these changes are most obvious when memory is
tested with recognition. Based on the notion th a t recall depends heavily on
interitem elaboration, whereas recognition is increased by intraitem
integration (Mandler, 1979), it has been suggested th a t maintenance
rehearsal causes repetition of the features related to the physical aspects
of items, whereas elaborative rehearsal adds relational information to the
traces (Greene, 1987; Lockhart & Craik, 1990).
2
The way the stimulus materials is presented is known to substantially
affect memory performance. One of the best known examples is the
"generation effect" (Jacoby, 1978; Slamecka & Graf, 1978). This effect
refers to a memory benefit for materials generated by subjects themselves
compared to m aterials supplied by the experimenter (e.g., Bobrow &
Bower, 1969; Schwartz, 1971). Generation effects have been demonstrated
on free recall, suggesting th a t some form of relational processing is
enhanced by generation (Hirshman & Bjork, 1988; McDaniel, Riegler, &
W addill, 1990). However, the effect of generation is strongest on
discrimination tests such as recognition (Begg, Snider, Foley, & Goddard,
1989), and it has been proposed th at the generation effect primarily is due
to the encoding of item-specific information, leading to a more distinctive
record of the generated items (Begg et al., 1989; Gardiner & Hampton,
1985).
Taken together, this brief discussion of current accounts of the effects of
elaboration, rehearsal, and generation illustrates the strong relationship
between the characteristics of memory traces and the encoding operations
performed a t input. It also highlights th a t the goodness of a particular
encoding operation depends on the nature of the cues present at retrieval.
Thus, given the assumption th a t a retrieval cue is effective only to the
extent th a t its informational content matches those of the trace, it is
possible to make inferences about the effect of an encoding operation on
the memory trace by observing the effectiveness of different cues (cf.,
Tulving, 1979). It is the overall purpose of this thesis to present an
analysis of the effect of a more recently developed encoding manipulation,
enactment, given a proper account of available retrieval information.
Memory of enacted events
The study of memory for enacted events was initiated by Engelkamp and
Krumnacker (1980), Saltz and Donnenwerth-Nolan (1981), and Cohen
(1981). In its basic form, this paradigm requires subjects to perform
mini tasks in response to verbal instructions (e.g., roll the ball) which the
subjects are instructed to try to remember. The typical control condition is
to present the same verbal commands without requiring the subjects to
perform the acts defined by the instructions. Following presentation,
3
subjects are instructed to make free recall of the verbal instructions. The
principle finding within this paradigm is th a t memory for enacted action
phrases generally is superior to memory for the same action phrases
w ithout enactm ent (e.g., Bäckman, Nilsson, & Chalom, 1986; Cohen,
1981; Engelkamp & Zimmer, 1985).
A slightly different procedure has also been used to study memory of
enacted events. As in the standard procedure, subjects are presented
verbal instructions th a t are encoded with or without enactment. However,
instead of a free recall task, subjects are given a cued recall task. A cueword from the verbal instructions is presented, and subjects are
instructed to complete the instruction by recalling the rest of the sentence.
Enactment has been found to substantially increase memory performance
also with this procedure (Saltz, 1988; Saltz & Donnenwerth-Nolan, 1981).
Following Cohen (1981), enacted action phrases will here be referred to as
S P T s (Subject-Performed Tasks), nonenacted action phrases will be
referred to as VTs (Verbal Tasks), and the enactm ent effect will be
referred to as the SPT-effect. In addition, a few studies have included a
condition involving performance by the experim enter instead of the
subjects. This m anipulation will be referred to as E P T (ExperimenterPerformed Task).
At this point, I would like to highlight the distinction between learning of
motor skills and memory of SPTs (cf., Cohen, 1989a). This distinction
relates to the distinction between procedural memory and episodic
memory (e.g., Tulving, 1987). The study of acquisition of motor skills has a
long history (see e.g., Adams, 1969a), and relevant examples of motor
tasks are the Line-Drawing test and the Rotary Pursuit test. The object in
the learning of motor skills is to achieve efficiency in reproduction of
movement patterns. In contrast, the object in SPT memory is to remember
as many commands as possible from a study trial. Moreover recall is in
the form of verbal descriptions; not reproduction of action patterns.
It is evident from the literature th a t it is possible to look a t the SPT
m anipulation in, a t least, two different ways. In the early papers by
Engelkamp and Krumnacker (1980) and by Saltz and Donnenwerth-Nolan
(1981), enactment was seen as a way of improving memory performance.
Engelkamp and Krumnacker set out to test the hypothesis th a t motor
processes, in addition to verbal and imaginai processes, influence recall
4
performance, and Saltz and Donnenwerth-Nolan had the specific purpose
of investigating how motoric enactm ent facilitates sentence memory.
Quite opposite, Cohen (1981) used the SPT task as a specific form of
memory m aterials rath er than as a form of encoding support, and the
purpose of the Cohen paper was to test the generalizability of some
memory laws established for free recall of word lists by using SPTs.
I prefer to view the SPT manipulation as a form of encoding support
rather than as a specific form of memory materials. Still, the papers to be
presented in the empirical section of this thesis are relevant for both of
these aspects of memory for enacted events. Next, findings th at have led to
the suggestion th a t memory of SPTs and VTs are based on different laws
will be discussed. That section is followed by a discussion of theoretical
explanations of the SPT effect.
Separate laws for memory of enacted and nonenacted events
Cohen (1981) set out to test the generality of some memory laws2 by using
members from two different event classes; one-way events (e.g., words)
and two-way events (e.g., SPTs). The term one-way event was used to
define a class of events in which subjects do not exert any observable effect
on the environment, whereas the class of two-way events involves the
observable manipulation of the environment by subjects. The rational for
the study was th at to the extent th a t memory laws exist, these laws have
been established by using one-way events and nothing is known about
their generalizability to other event classes.
The results of the Cohen (1981) study suggested lack of generality for a few
of the laws tested. Specifically, whereas there was a strong positive
recency effect for SPTs as well as for VTs, SPT recall did not show any
effect of primacy. Also, subjects self-reports indicated th at they did not use
active memorisation strategies for SPT lists, but they did so for word lists.
Moreover, the levels of processing manipulation did not affect SPT recall.
2 The concept of law was used by Cohen (1981) in a rather liberal sense to refer to reliable
memory effects such as the primacy effect and the levels-of-processing effect. Cohen
(1985) has acknowledged that laws and effects are not synonymous, and a more proper
term for the "laws" to be discussed in this section is therefore "effects". In this section, I
will, however, use the terminology adopted by Cohen (1981). A more thorough discussion
of the concept of law is given in the General discussion section.
5
In all, these memory-law violations were interpreted as suggesting th a t
traditional encoding mechanisms are of little importance in SPT recall.
A couple of studies involving subject-related variables provided further
support for this interpretation. Cohen and Stew art (1982) demonstrated
th a t the typical developmental effect found in verbal recall did not
significantly show up in SPT recall; 9-year-old childrens performance
was comparable to the performance of 13-year-old children. Since it has
been claimed th a t developmental effects should show up in strategic
tasks, Cohen and Stewart interpreted this finding as indicating th a t SPTs
are nonstrategically encoded. Comparable levels of recall for educable
mentally retarded subjects and nonretarded controls was demonstrated by
Cohen and Bean (1983). The mentally retarded subjects were presumed to
have general strategic deficits. For this reason, the lack of difference in
memory performance can be seen as supporting the interpretation th a t
SPT encoding is nonstrategic.
F urther experimental study revealed additional differences between SPT
and VT memory. Cohen (1983) showed th a t labeling some items as more
im portant to remember than others had a strong effect on recall of VTs,
but only a minimal effect on SPT recall. In th a t study it was also shown
th a t subjects were rath e r good a t predicting which VTs they were to
recall, but not which SPTs should be easy to recall. In addition, Nilsson
and Cohen (1988) found th a t th e generation effect and encoding
elaboration had no effect on SPT recall (see also Nilsson, Nyberg, &
Kormi-Nouri, 1992).
Taken together, the differential effects of various experimental- and
subject-related variables can be taken as suggesting th a t SPTs and VTs
obey different memory laws. That the basic laws of SPT and VT memory
are different has also been proposed by others (Nilsson & Bäckman,
1989a)/ Nilsson and Bäckman added two SPT-VT dissociations to those
described above. First, they pointed out th at intentionality to learn does not
affect SPTs (e.g., Kausler, Lichty, & Freund, 1985). Second, SPTs and VTs
behave differently with respect to the phenomenon of recognition failure of
recallable items (Nilsson, Law, & Tulving, 1988; see also Svensson &
Nilsson, 1989).
Cohen has, as stated above, offered an explanation of the different
patterns of results for SPTs and VTs in term s of lack of memorisation
6
strategies in the case of SPTs (see e.g., Cohen, 1989a). That is, during
standard instructions subjects do not appear to use memorisation
strategies to improve the encoding of SPTs. This may be due to the fact
th at subjects do not know how to improve encoding of SPTs (Cohen, 1989a;
see also H elstrup, 1987). Thus, in the sense th a t subjects do not use
strategies when encoding SPTs, SPT learning can be said to be automatic.
The studies to be presented in the empirical section of this thesis have
implications for the notion th at the basic laws of SPT and VT memory are
different (Study I), and for the "strategy-explanation" of these memory
law violations proposed by Cohen (Study II).
S tarting w ith the issue w hether memory of enacted and nonenacted
events are based on different laws, it can be questioned w hat criteria
should be fulfilled to motivate the introduction of new laws of memory. For
example, the lack of primacy effect for SPT recall has, as described above,
been seen as a rather strong argument in favour of the notion th a t SPT
recall obey different laws than VT recall. Helstrup (1986) has, however,
argued th a t building memory laws based on differences in serial position
curves is suspicious. Virtually any variant of the serial position curve has
been shown possible to produce by various experimental manipulations.
A stronger criterion would be if the superior memory performance of
SPTs over VTs interacts with rate of forgetting such th a t the magnitude of
the SPT effect increases over time. This is because, so far, degree of
original learning has not been demonstrated to affect rate of forgetting
(Slamecka & McElree, 1983).
Slamecka and McElree (1983) pointed out th at the large amount of studies
of the effect of encoding operations on long-term retention stands in sharp
contrast to the very few studies of the effect of encoding operations on
normal forgetting (i.e., forgetting th at occurs with the passage of time). In
fact, based on a review of the literature, Slamecka and McElree concluded
th at the literature provided no firm answer to the question of how degree
of learning affects forgetting. They therefore set out to test this issue
empirically, and found th a t long-term forgetting of verbal lists is
unaffected by the degree of original learning. Slamecka and McElree
(1983) based this conclusion on test of vertical parallelism. Loftus (1985)
has favoured a method involving analysis of horizontal parallelism, and
by using this method he has found th a t forgetting is slower for higher
7
degrees of initial learning. Slamecka (1985) has, however, criticised this
method, and he argued th a t the method suggested by Loftus (1985)
involves a confounding with the ages of the lists being compared. The
question of how to analyze forgetting curves remains a critical issue, but
most, if not all, studies of normal forgetting have involved test of vertical
parallelism. This method was also used in the empirical section of the
present thesis.
Thus, the strong effect of degree of original learning on long-term
retention has not been found to be reflected in the rate of forgetting.
Therefore, a reflection of the initial superiority in memory performance of
SPTs over VTs on the rate of forgetting could be taken as support for the
view th a t the basic laws of enacted and nonenacted memory are different.
In fact, such a finding would suggest th a t the underlying memory
processes involved in SPT- and VT memory are different; a view
previously advanced by Nilsson and Bäckman (1989b). This is because the
forgetting curves for memory abilities assumed to be mediated by separate
underlying memory systems are quite different. One relevant example is
the slopes of the forgetting curves for episodic memories and memory for
continuous motor skills. Most memory theorists agree th a t it is likely th at
memory of episodes and memory of skills are m ediated by different
memory systems in the brain (e.g., Squire, 1992; Tulving & Schacter,
1990), and the slopes of the forgetting curves for these different types of
m aterials are also fundamentally different (e.g., Adams, 1969b).
Taken together, it has been argued th a t serial position curves are hardly
constancies on which to build laws of memory (Helstrup, 1986). It appears
th a t different rates of forgetting would be a stronger support for the notion
of different laws, and one of the purposes of the present thesis was to
compare the slopes of the forgetting curves for SPTs and VTs (Study I).
Turning now to the question of how to explain the apparent memory law
violations, Cohen's suggestion of SPT learning being automatic rath er
th a n strategic implies th a t recall of SPTs should be independent of
subjects' age (cf., H asher & Zacks, 1979). In line with this expectation,
Bäckman and Nilsson (1984, 1985) found an eliminated age effect when
SPTs were used as the to-be-remembered m aterials. Bäckm an and
Nilsson (1984, 1985) compared free recall performance for young subjects
(approximately 20 years of age) and old subjects (approximately 70 years of
8
age). Clearly, the finding by Bäckman and Nilsson of an eliminated age
effect for SPTs supports Cohen's assum ption of SPT learning being
automatic.
However, although a few studies have replicated the finding of an
eliminated age effect (Cohen & Faulkner, 1990; Dick, Kean, & Sands,
1989), several studies have found th a t age differences indeed influence
SPT recall (e.g., Cohen, Sandler, & Schroeder, 1987b; Guttentag & Hunt,
1988; Knopf & Niedhardt, 1989; Nilsson & Craik, 1990). Findings of age
differences cast doubts on Cohen's "strategy-explanation" of the different
data patterns obtained for SPTs and VTs. It is therefore urgent to explore
the reasons as to why the aging effect sometimes is eliminated, and
sometimes present (or only reduced).
Differences in the experimental procedures have been put forward as a
potential solution to the puzzle (see Cohen 1989a; Engelkamp & Cohen,
1991). The specific items used may be one im portant difference. In
general, commands vary greatly in recallability (e.g., Cohen, 1989a), and
recent findings suggest th a t item type can interact with subject age
(Norris & West, 1991). Variations in list length have also been considered
in this context (Cohen et al., 1987b). Cohen et al. found reliable aging
effects in SPT recall for long lists (37 items), but not for short lists (14
items), suggesting th a t effects of aging show up when the task is more
demanding (for sim ilar conclusions, see Knopf, 1991; Norris & West,
1991). However, an interpretative difficulty with the finding by Cohen et al.
(1987b) is th a t VT recall for short lists was only marginally more affected
by age than was SPT recall. In addition, Kausler and co-workers have
consistently found aging effects in memory of subject-performed activities
using short lists (e.g., Kausler et al., 1985). Obviously, the picture is not
clear, and the relation between age and SPT recall was therefore studied
in the present thesis (Study II) using exactly the same materials (12-item
lists) as in the first study reporting an eliminated age effect (Bäckman &
Nilsson, 1984).
In this context it is warranted to stress that not only studies of the relation
between SPT recall and age have yielded mixed results. Rather, I consider
lack of replicability as a central problem in this area of research. Relevant
examples of variables th at have generated divergent outcomes are levelsof-processing, developmental effects, and primacy. These variables will be
9
discussed at some length in the General discussion section. Furthermore,
it is also true th a t many of the dissociations demonstrated between SPT
and VT-recall are based on single studies only (cf., Nyberg, Nilsson, &
Bäckman, 1992). Thus, there is an obvious danger in th a t future research
will reveal additional inconsistencies. N evertheless, it is a general
consensus on the issue of primary concern in here; the enactment effect is
a highly reliable phenomenon (cf., Cohen, 1989a).
Theoretical explanations of the enactment effect
The major distinguishing feature of SPT learning is the involvement of
e n a c tm e n t, and all SPT researchers would probably agree th a t an
explanation of the SPT effect has to involve the motor component.
The position taken by Engelkamp and Zimmer (e.g., 1985) lends special
im portance to the motor component of SPTs. These authors have
motivated their strong emphasis on the motor aspect by suggesting th a t
enactm ent improves item-specific encoding (Hunt & Einstein, 1981), and
thereby produces the SPT effect (see e.g., Engelkamp, 1990; Engelkamp &
Cohen, 1991). Engelkamp and Zimmer have modified Paivio's dual-code
theory in the sense th at they have added a motor system and a conceptual
system to the theory proposed by Paivio (Paivio, 1971). Activation of the
motor memory results from performing an action (Engelkamp & Zimmer,
1985), and activating the motor system is assum ed to improve itemspecific encoding (i.e., encoding of information connected to the to-beremembered information).
Cohen has also assigned particular importance to the motor component
in explaining the SPT effect (see e.g., Cohen, 1989a). According to Cohen,
the actual p attern of motor activity is unim portant. As long as some
appropriate activity is involved, memory performance benefits from
enactment. As to how enactment improves memory, Cohen has suggested
th a t enactment facilitates retrieval by adding a dimension to the memory
trace (Cohen, 1989a).
The position taken by Cohen resembles the explanation favoured by Saltz
in the sense th a t Saltz has also suggested th a t enactm ent facilitates
sentence recall by resulting in a motoric image or trace (Saltz, 1988; Saltz
10
& Donnenwerth-Nolan, 1981). Saltz assumes th at enactment helps specify
the meaning of the various concepts th at are a part of a sentence, thereby
improving recall of the sentence. In a sentence like "the boy threw the
ball", the act of throwing is an attribute of the boy. Enactment would lead
to a more specific activation of the attribute (throwing) of the concept (boy)
than ju st reading the sentence. Due to this more specific activation, the
concept is assumed to be registered more precisely, leading to less overlap
with other concepts and thereby increased retention (cf., Klein & Saltz,
1976).
Also Bäckman and Nilsson put strong emphasis on the motor component
in explaining the SPT effect (Bäckman & Nilsson, 1984, 1985; Bäckman,
1985, Bäckman et al., 1986). In essence, this framework explains the SPTeffect by referring to the richer encoding situation in the case of SPTs.
Several sensory systems are involved during encoding of SPTs, and each
SPT comprises a number of different features on which the encoding can
be based (e.g., motor features and features of color, texture, and shape).
As a consequence of the multimodal and rich properties of SPTs, it is
proposed th at two kinds of information can be involved in the SPT task (the
verbal commands and the motor actions), whereas only information about
the verbal commands is available in the case of VTs.
It should be evident from the above discussion th a t the motor component
holds a central position in explanations of the SPT effect. However, it m ust
be observed th a t there has been considerable disagreement as to whether
motor activity on the part of the subject is a prerequisite for the SPT effect.
This issue relates to the question of whether motor processing has to be
overt to facilitate memory performance, or if covert (i.e., imagined)
actions also produce an SPT effect. Starting with the question of physical
motor activity, Cohen does not assume th a t self performance is of
particular importance for the SPT effect. In support of this view, Cohen
has repeatedly shown th a t SPTs are not significantly better remembered
than EPTs (Cohen, 1981, 1983; Cohen et al., 1987a), and Cohen considers
SPTs and EPTs as memorially very similar (Cohen, 1989b). In contrast,
Engelkamp and Zimmer (1983, 1985) claim th a t there is a qualitative
difference between SPTs and VTs, and they have found th a t SPTs are
better remembered than EPTs.
11
T urning to the distinction betw een overt and covert enactm ent,
Engelkamp and colleagues have shown th a t covert enactm ent improve
performance (cf., Engelkamp & Krumnacker, 1980; Engelkamp, Zimmer,
& Denis, 1989). Similarly, Saltz has found th a t covert enactment actually
can lead to a higher performance th a n overt enactm ent (Saltz &
Donnenwerth-Nolan, 1981; see also Saltz, 1988). Interestingly, Bäckman
(1985) reported results suggesting th a t the importance of overt enactment
may be dependent on the age of the subjects. Bäckman presented subjects
sentences like "roll the ball", and sim ultaneously the objects in the
sentences were presented. H alf of the subjects were allowed to act
motorically, whereas the other half encoded the sentences without motor
action. The results showed no difference in memory performance between
the two task conditions for young subjects. In contrast, elderly subjects'
performance was significantly decreased when the motor component was
excluded. It was suggested th a t activation of the tactual modality and
presence of motor aspects was a critical prerequisite for the elderlys high
performance on SPTs. To explain the p attern of results for the young
subjects, it was suggested th a t young subjects might be capable of
recoding the materials so th a t motor aspects become a part of the stored
information. Visual imagery was seen as a plausible type of recoding.
Thus, the young subjects' high performance when the motor component
was excluded was explained in term s of subjectively initiated covert
enactm ent.
H elstrup has also found th a t imagined acts are as well remembered as
performed acts, and he has argued th a t act recall produces sim ilar
resu lts irrespective of w hether the acts are concretely performed,
symbolically performed, or imagined (Helstrup, 1986, 1987). This is
consistent with the problem-solving approach favoured by Helstrup. In
term s of this approach, motor attrib u tes do not comprise a separate
source pf information. Rather, whether or not enactment leads to superior
memory performance than nonenactment is suggested to depend on the
specific encoding conditions. Thus, if the orienting responses to the task
m aterial engages subjects, and the situation involves sufficiently useful
memory cues (e.g., imaging oneself performing the acts), the addition of
motor cues will not make any difference (see Helstrup, 1987). Obviously,
this view differs from the strong emphasis on the motor component found
in most other explanations of the SPT effect.
12
Another distinguishing feature of SPT learning is involvement of objects.
However, this feature is not a part of all experimental paradigms. That is,
whereas the paradigm used by Cohen and by Bäckman and Nilsson
involves real objects, the procedure followed by Engelkamp and Zimmer
and by Saltz does not involve presenting subjects with real objects.
Instead, the subjects symbolically perform the actions defined by the
instructions, and a clear effect of enactment is still obtained (see also
Helstrup, 1986). Presumably due to the lack of involvement of concrete
objects in the procedure followed by the latter research groups, the object
component does not hold a central position in explanations of the SPT
effect. However, as noted above, the object component plays an important
role in the framework proposed by Bäckman and colleagues. This
framework assumes th a t the SPT effect is based on the multimodal, rich
encoding of SPTs, and the richness of the encoding is considered to be
dependent on the sensorial richness of the stimulus event. SPTs involving
manipulation of real, concrete objects (e.g., "roll the marble"; "bounce the
ball") should be more apt for a rich encoding than SPTs not involving such
objects (e.g., "lift your arm"; "point at the door"), and therefore better
recalled. This is because SPTs involving external objects should comprise
a larger number of features on which the encoding can be based (cf.,
Bäckman et al., 1986).
Type of objects has also been considered in analyses of interitem
differences in SPT recall (Cohen et al., 1987a). Cohen et al. distinguished
between SPTs involving extra-environmental objects (e.g., "roll the ball")
and SPTs not involving extra-environmental objects (e.g., "point a t the
door"). It was hypothesized th at since the extra-environmental objects are
removed immediately following event presentation, the environm ent
should provide poorer retrieval cues for SPTs involving this type of objects,
and the results supported this hypothesis. In the same study, it was
attempted to experimentally separate the action and object components of
action events in order to find out which component th a t prim arily
determines recall probabilities of action events. They found th at the action
component had the major role; objects played only a subsidiary role.
The importance of objects for the SPT effect as well as for interitem
differences in event memory, and the significance of the motor
component, was further addressed in the present thesis (Study III).
13
More recently, it has been hypothesized th a t SPTs, in addition to motoric
information, also add conceptual information (Nilsson & Craik, 1990).
N ilsson and C raik dem onstrated w hat they term ed a d d itiv e and
interactive effects between SPTs and various variables. Additive effects of
variables are expected to show up for variables th a t induce information
th a t is orthogonal to th a t induced by SPTs. Given th a t SPTs add motoric
information, it is thus expected th a t SPTs act additively with variables
th a t do not induce motoric information. Such effects have, for example,
been demonstrated for list structure and retrieval cues (Nilsson & Craik,
1990).
Interactive effects should occur for variables th a t induce encoded
information th a t overlaps with information added by SPTs. Curiously, a
few variables th a t not add motoric information have been found to act
in teractiv ely w ith SPTs. For exam ple, th e levels-of-processing
m anipulation has been shown to act interactively with SPT effects:
W hereas memory of verbal information benefits from a deep encoding,
SPT memory is only little affected by processing level (e.g., Cohen, 1981;
Nilsson & Craik, 1990). A possible explanation to the interactive effect
between the SPT- and the levels-of-processing manipulations is th a t SPTs,
in addition to motoric information, add information induced by the levelsof-processing m anipulation, and th a t th eir dual occurrence contributes
nothing further. Interactive effects have also been reported between SPTs
and the generation effect (Nilsson & Cohen, 1988). Both levels of
processing and generation have been suggested to enhance recall through
the addition of conceptual information (e.g., Craik & Lockhart, 1972; Graf,
1982). For this reason, Nilsson and Craik proposed th at SPTs, in addition
to motoric information, add conceptual information.
The proposal th a t SPTs add conceptual inform ation has im portant
implications for theories of SPT memory since it implies th a t one basis for
the SPT effect would be inducement of a richer conceptual representation.
However, as acknowledged by Nilsson and Craik (1990), the empirical
evidence supporting this proposal is sparse. One of the studies reported in
the empirical section of this thesis therefore tested the hypothesis th a t
enactm ent leads to inducem ent of a richer conceptual representation
(Study IV).
14
Overview of the em pirical studies
Study I (Nilsson, Cohen & Nyberg, 1989).
Nilsson, Cohen and Nyberg (1989) compared the forgetting rates for SPTs
and VTs. The first experim ent used the procedure for m easuring
forgetting suggested by Slamecka and McElree (1983). That is, no attem pt
was made to equate initial recall levels for the encoding manipulations
compared. Subjects were presented with 3 12-item lists of SPTs and 3 12item lists of VTs. The VTs were typed on cards which were shown to the
subjects, and also read by the experimenter. For SPTs, the instructions
were read aloud by the experim enter. The presentation ra te was
approximately 5 s per item. A test of immediate free recall (IFR) was
given after each list. In addition, one third of the subjects were given an
unexpected final free recall (FFR) test two minutes after recalling the
items from the last presented list. Another third were given the same test
after 1 day (24 hours), and the last third of the subjects were given the
same test after one week.
Analyses of the FFR-data showed a main effect of m aterials (an SPTeffect), and a main effect of retention interval (showing th a t forgetting
occurred). The critical interaction between m aterials and retention
interval was, however, nonsignificant. The lack of interaction indicates
similar forgetting rates for SPTs and VTs.
Experim ent 2 used a slightly different procedure for m easuring
forgetting. In this experiment, effort was investigated in trying to equate
the initial recall values (i.e., to eliminate intercept differences; cf., Nelson
& Vining, 1978). This was done by varying the number of presentations
during acquisition (half of the items were presented once and the other
half twice).
The m aterials and the procedure were basically the same as in
Experiment 1. Only two SPT lists and two VT lists were, however, used.
The results showed, once again, a nonsignificant interaction between
encoding condition and retention interval. An analysis of the effect of the
attem pt to equate the initial recall values showed th at this attem pt failed;
one p resentation of SPTs produced a significantly higher recall
15
performance than did two presentations of VTs. Analysis of the forgetting
functions for these conditions only, revealed a nonsignificant interaction.
In Experiment 3 an additional attem pt was made to equate the initial
recall values. SPTs were presented either once or twice, whereas the VTs
were presented either three or four times. The retention intervals differed
from the first two experiments; subjects were tested after 2 min, after 6
hours, or after 24 hours. In all other im portant respects, the experimental
design was similar to the design in Experiments 1 and 2.
Analyses of the IFR-data showed th at this time, the attem pt to equate the
in itial recall values was successful; the performance for four tim es
presented VTs was not significantly different from the one or two
presentations of SPTs. However, once again, no significant interaction
was found, leading to the conclusion th a t long-term forgetting functions
for SPTs and VTs do not differ. In turn, this was seen as suggesting th at
the mechanisms underlying SPT and VT recall are not fundamentally
different.
Finally, the drop in performance between IFR and the first FFR test
(given after a 2 minutes retention interval) was compared for SPTs and
VTs. Visual inspection of the data suggested th at this drop was somewhat
more pronounced for VTs th a n for SPTs. This impression was given
p artial support by analyses of the data from each of the experiments, as
well as for an analysis of data collapsed across experiments.
Taken together, although the long-term forgetting functions did not differ,
the data suggested th a t there is a somewhat more marked forgetting rate
over the first few minutes after study for VTs compared to SPTs.
Study n (Nyberg, N ilsson, & Bäckman, 1992).
Nyberg, Nilsson, and Bäckman (1992) tried to replicate the studies
presented by Bäckm an and Nilsson (e.g., 1984, 1985) showing an
elim inated age effect for SPTs. In addition, the drop in performance
between IFR and FFR was compared for SPTs and VTs. Following
Bäckman and Nilsson (1984), both recall of sentences and recall of nouns
from the sentences were used as verbal controls. These verbal conditions
will collectively be referred to as VTs.
16
One group of elderly subjects (M = 69.3) and one group of young subjects
(M = 19.1) were tested. Subjects were presented with six 12-item lists
which were the same materials as used by Bäckman and Nilsson (1984).
Items in two of the lists were presented as SPTs, in another two of the lists
as sentences, and in still another two only the noun in each action phrase
was presented. The lists were counterbalanced across m aterials, and
order of list presentation was counterbalanced across subjects. The action
phrases and the nouns were presented by means of a slide projector at a
rate of 5 sec per item. Before presentation of each list, subjects were
instructed to try to remember as many items as possible, and after
presentation of each list there was an IFR test. Fifteen minutes after
presentation and test of the last list, subjects were given a FFR test of all
72 items.
Aging effects were predicted to show up for VTs but not for SPTs (cf.,
Bäckman & Nilsson, 1984, 1985). Moreover, based on Nilsson, Cohen, and
Nyberg (1989), the drop in performance between IFR and FFR was
predicted to be more pronounced for VTs than for SPTs.
The results confirmed the prediction for the performance drop by showing
less forgetting between IFR and FFR for SPTs compared to VTs. However,
the aging data showed a superior memory performance for the young
subjects over the elderly subjects for VTs as well as for SPTs. The
differences in recall were, however, more pronounced for the VTs than
for the SPTs.
The results were interpreted as showing th a t the age effect is less
pronounced for SPTs than for VTs since the encoding situation involves a
high degree of cognitive support. Differential sensitivity to proactive
interference was suggested as explanation to the difference in forgetting
rates over the initial minutes of retention between SPTs and VTs (cf.,
Nilsson & Bäckman, 1991).
Study III (Nyberg, Nilsson, & Bäckman, 1991).
Nyberg, Nilsson, and Bäckman (1991) examined the basis for the SPTeffect in two experiments, and explored the question why some SPTs are
easier to recall than others in one additional experiment.
17
Experiment 1 focused on the importance of the object component for the
SPT effect. Subjects studied a mixed list of SPTs and VTs. Half of the items
involved extra-environmental objects, the other half did not. The items
were counterbalanced across materials. Subjects were instructed to try to
remember as many items as possible for a subsequent test of free recall.
Based on the theory proposed by Bäckman and Nilsson (1984, 1985), a
larger SPT effect was predicted for SPTs involving extra-environmental
objects (e.g., "open the book”; "lift the spoon") than for SPTs not involving
extra-environm ental objects (e.g., "touch your ear"; "cross your legs")
since the former type of items should make the encoding environment
more supportive. Note th a t this prediction is in conflict with the results by
Cohen et al. (1987a, Exp. 1), who found a tendency for no-object events to be
recalled better than object events.
The results did not confirm the prediction. There was no difference
between SPTs involving extra-environm ental objects and SPTs not
involving such objects. In fact, there was a nonsignificant tendency for a
higher memory performance for SPTs not involving extra-environmental
objects (cf., Cohen et al., 1987a, Exp. 1). This finding indicates th a t the
object component may not be a critical factor for the advantage of SPTs
over VTs.
The second experim ent focused on the importance of the num ber of
modalities activated during encoding, and the importance of the action
component. A similar design and the same m aterials as in Experiment 1
were used. The procedure differed in one respect: When an action phrase
involving an extra-environmental object was presented as a VT, the object
was shown to the subjects. They were not allowed to touch the objects. It
was predicted th a t SPTs involving extra-environmental objects would give
a higher memory performance than VTs involving extra-environmental
objects since the SPTs involved enactm ent and m anipulation of the
objects, thereby activating an additional modality and increasing the
richness.
The results showed th a t SPTs not involving extra-environmental objects
were best remembered, and, opposite to the prediction, there was no
difference in memory performance between SPTs and VTs involving
extra-environm ental objects. This finding shows th a t the memory
performance does not increase as a function of the number of activated
18
modalities during encoding, and suggests th a t the action component is
not especially critical for the memory performance.
Experiment 3 examined why some SPTs are easier to recall than others.
In so doing, the im portance of compatibility between encoding and
retrieval was studied. This was accomplished by presenting subjects a
mixed list of SPTs and VTs. The items were counterbalanced across
materials, and were of four different kinds: Action phrases involving (1)
body parts, (2) effects in the laboratory, (3) kitchen utensils, and (4) items
not belonging to specific categories. It was predicted th a t items involving
objects present both during encoding and retrieval would be best
remembered [i.e. categories (1) and (2)]. Whereas this prediction is in line
with Cohen et al. (1987a), a richness of encoding view (Bäckman &
Nilsson, 1984, 1985) would predict the highest performance for categories
(3) and (4). The results confirmed the prediction by showing a superior
memory performance for categories (1) and (2) for both SPTs and VTs.
The overall impression from Experiments 1 and 2 was th a t it is not
possible to partial out a single component as the cause of the SPT-effect.
The results showed th a t provision of extra-environmental objects does not
enhance SPT recall. The finding th a t SPTs and VTs involving extraenvironmental objects were remembered to the same extent indicated th a t
multimodality does not lead to a superior memory performance than does
bimodal activation. Also, th a t SPTs and VTs were remembered to the
same extent suggested th a t enactment by the subjects is not of special
significance for the SPT-effect.
Experiment 3 pointed to the importance of a high degree of compatibility
between encoding and retrieval. This result suggested th a t the logic of the
encoding specificity principle (e.g., Tulving, 1983) can be extended from
the domain of verbal m aterials to the domain of action events. It was
concluded th a t it is sufficient to consider the more supportive encoding
situation in the case of SPTs in explaining the SPT-effect, but th a t the
relation between encoding and retrieval m ust be taken into account in
trying to explain why some SPTs are more memorable than others.
Study IV (Nyberg & Nilsson, 1992).
Nyberg and Nilsson (1992) set out to test the hypothesis th a t SPTs add
conceptual information to the memory trace (Nilsson & Craik, 1990). In so
19
doing they studied the effect of the SPT-manipulation on implicit memory
performance (Graf & Schacter, 1985). Several studies in the domain of
implicit memory have shown th a t performance on conceptually driven
im plicit tests (e.g., general knowledge retrieval; category association)
benefits from encoding operations involving conceptual elaboration (e.g.,
Blaxton, 1989; Hamann, 1990; Rappold & Hashtroudi, 1991; Srinivas &
Roediger, 1990). The basic idea was therefore th a t if SPTs add conceptual
inform ation, SPTs would produce g reater prim ing th an VTs on a
conceptually driven implicit test.
In Experiment 1, subjects were presented with 30 imperatives, including
5 buffer items. To allow evaluation of the priming effect, two different
study lists were used. The target nouns in each study list were from five
different semantic categories (5 nouns / category). Each imperative was
typed on a separate sheet, and presented for 8 s. H alf of the items in the
study list were presented as SPTs, and the other half as VTs. Following
presentation, subjects were given two different implicit tests (category
association and stem completion), followed by a test of free recall. The
items in the study lists were presented in blocks of SPTs and VTs, and the
order between the blocks and the order of the im plicit tests were
counterbalanced across subjects.
It was predicted th a t if conceptual information is added by SPTs, the
am ount of prim ing on the conceptually driven implicit test, category
association, would be higher for SPTs than for VTs. Performance on datadriven implicit tests, such as stem completion, has been seen as not being
affected by conceptual elaboration (e.g., Roediger, Weldon, & Challis,
1989). However, recently Challis and Brodbeck (1992) showed th at also this
type of implicit test can be affected by conceptual encoding manipulations.
A higher performance on stem completion was therefore predicted for
SPTs.
The results showed the standard SPT-effect in free recall. However,
opposite to the predictions, prim ing on the im plicit tests was not
significantly higher for SPTs than for VTs. Since priming on conceptually
driven tests repeatedly has been found to be increased by manipulations
involving conceptual elaboration, this suggests th a t SPTs do not add
conceptual information. However, to test the possibility th a t the category
association te st is not sensitive to semantic elaboration of the kind of
20
m aterials used in the present study (verbal imperatives) an additional
encoding manipulation, generation, was included in Experiment 2.
In Experiment 2, three different study manipulations were used; SPTs,
VTs, and generation. The generation condition involved generation of the
noun in the imperatives in which the first and the last letter of the noun
was switched (e.g., "earblm” for ”marble"). The items in the study list
were presented in a mixed fashion, and the data-driven implicit test (stem
completion) was not included. In all other respects, the experimental
design was similar to the design used in Experiment 1.
Generation was predicted to produce a substantial prim ing effect on
category association, and, given th a t SPTs add conceptual information,
the same was predicted for SPTs (i.e., in such a case there should be a
parallel effect of the SPT and Generate conditions). Otherwise, the
amount of priming was predicted to be the same for SPTs and VTs.
The results showed th a t the only condition producing reliable priming on
category association was generation. Also, the difference in priming
between SPTs and VTs was nonsignificant. In free recall, the pattern of
results was quite different. In this test, there was a highly significant
SPT-effect, and memory performance for SPTs was higher th an for
generate items. There was also a significant interaction between type of
test and study condition.
Taken together, the results from the two experiments did not support the
hypothesis of SPTs adding conceptual information, thereby increasing
memory performance on free recall. Motor enrichm ent was instead
suggested as the primary cause of the SPT-efFect.
General discussion
The main findings of the empirical studies were (i) sim ilar forgetting
functions for SPTs and VTs; (ii) a reduced, but statistically significant,
aging effect for SPTs; (iii) lack of an SPT-effect when objects were
presented in VTs; (iv) a higher memory performance for SPTs not
involving extra-environm ental objects th an for SPTs involving such
objects; and (v) a non-significant SPT effect on a conceptually driven
implicit test. Next, implications of these findings for the notion of separate
21
laws for SPT and VT recall, and for explanations of the SPT effect, will be
discussed.
Memory laws
In evaluating the claim th a t the basic laws of enacted and nonenacted
memory are different (Cohen, 1981; Nilsson & Bäckman, 1989a), I will
follow the outline of potential laws of memory given by Cohen (1985).
Cohen suggested a definition of a memory law, saying th a t "a memory
law should be a statem ent about some empirical relationship in memory,
which has transsituational generality and which looks like it will be
around for some time to come (1985, p. 252). Note that, according to this
definition, it is not required th a t a memory law explains the reasons for
the em pirical regularity. This is consistent w ith the more general
definition of an empirical law, which states th a t an empirical law ”seems
to summarize simply some fairly directly observed regularity, whithout
attem pting to provide a theoretical explanation for it" (Holton & Brush,
1973, p. 158; see also Nilsson et al., 1988). Cohen (1985) tested the
tran ssitu atio n ality of the laws he proposed by comparing word list
memory with memory for SPTs. Cohen (1985, see also Cohen, 1981)
claimed th a t SPTs are essentially nonverbal events, and should thereby
m erit for test of transsituationality. I prefer to view the SPT task as verbal
memory for tasks th a t have been carried out (cf., H elstrup, 1987).
However, to be able to evaluate the proposal th a t SPTs and VTs obey
different laws, I will leave this difference aside.
The first law discussed by Cohen (1985) is related to the acquisition phase,
and states th a t the better something is learned the greater is the likelihood
th a t it will be remembered. Seven different acquisition effects feeding in to
this first law, including levels of processing and primacy, were presented.
All these seven acquisition effects supported the validity of the first law by
turning out to hold true for word-list memory (e.g., deep processing leads
to better word recall th an shallow processing). However, the levels of
processing and primacy effects are of special interest since they have been
found not to have any effect on SPT recall (Cohen, 1981), thereby
questioning the transsituationality of the first law. Since I mainly have
used the SPT task as a form of encoding support, and not as a specific
form of m aterials, the data presented in the empirical section of this
thesis are not relevant to the first law. I will, however, evaluate the
22
apparent lack of transsituationality for the first law by using data reported
in the literature.
S tarting w ith the primacy effect, it has been questioned w hether the
primacy effect really is absent in the case of SPTs. Specifically, it has been
proposed th a t since the level of the asymptote generally is higher for SPTs
than for VTs (see especially Bäckman & Nilsson, 1984), this might level
out the entire prerecency portion of the serial-position curve for SPTs
(Bäckman, Nilsson, Herlitz, Nyberg, & Stigsdotter, 1991). Ordinary serial
position effects have also been reported for SPT recall after the induction of
active processing during encoding (Helstrup, 1987, Study 3).
Turning to the levels of processing effect, the relevant literature shows a
mixed picture: Although Cohen's (1981) original finding of no effect of the
levels-of-processing manipulation on SPT recall has been replicated (e.g.,
Helstrup, 1987), depth of processing has indeed been found to affect SPT
retrieval. Nilsson and Craik (1990) showed an increase in SPT recall
following deep processing - the increase was smaller though than for VT
retrieval. Furtherm ore, Zimmer (1992) has dem onstrated comparable
levels of processing effects on recall of SPTs and VTs. It appears, then,
th a t it is possible to include SPT recall in the first law (cf., Cohen, 1985, p.
271).
The second law discussed by Cohen (1985) concerns fo r g e ttin g .
Transsituational generality of this law is provided by comparable recency
effects for SPTs and VTs (e.g., Bäckman & Nilsson, 1984; Cohen, 1981).
F urther support is provided by the finding of comparable slopes of the
forgetting functions for SPTs and VTs, reported in the empirical section of
this thesis (Study I). This result adds to previous demonstrations of no
effect of degree of original learning on the slope of forgetting curves
(Slamecka & McElree, 1983). Similarly, manipulations of encoding levels
(Craik & Lockhart, 1972) have failed to affect the slope of forgetting curves
(Nelson & Vining, 1978). Thus, an im portant implication of the finding of
similar slopes of forgetting curves for SPTs and VTs in Study I is th at it
suggests a strong sim ilarity between the specific encoding operation
under investigation and other encoding manipulations. In addition, this
finding indicates th a t the mechanisms underlying SPT recall and VT
recall are quite similar (cf., Cohen, 1985; Helstrup, 1987), thereby refuting
23
suggestions th a t qualitatively different memory processes are involved in
SPTs and VTs (e.g., Nilsson & Bäckman, 1989b).
The third law discussed by Cohen is related to retrieval. The concept of
encoding specificity (Tulving, 1983; Tulving & Thompson, 1973) was used
by Cohen (1985) to formulate this law as the closer the match between the
encoding and retrieval conditions the better memory performance. The
results of the component analysis presented in the empirical section of
this thesis (Study III, Exp. 3) showed th at SPTs involving objects th a t were
present during both presentation and test were remembered the best. This
finding replicates results reported by Cohen et al. (1987a), and was
interpreted as suggesting th a t the idea of encoding specificity can be
extended from the domain of verbal m aterials to the domain of action
events. This finding thus provides support for transsituationality of the
third law.
Based on the above discussion of the memory laws proposed by Cohen
(1985), it does not seem to be any need of separate laws for two-way events
such as SPTs (cf., Cohen, 1981). This claim is further supported by
examination of one additional possible law suggested by Cohen (1985);
in d ivid u a l differences. T ranssituationality of this additional law is
provided by reliable individual differences in SPT recall (Cohen, 1984) and
the emerging trend th at SPT memory is affected by age (cf., Engelkamp &
Cohen, 1991); a trend th at was supported by the finding reported in the
empirical section of this thesis of an age effect on SPT recall (Study II).
Since short lists were used in this study, the finding suggests th a t the
trend might be rather general in nature, and hold true not only when the
tasks are relatively demanding (cf., Cohen et al., 1987b; Engelkamp and
Cohen, 1991). In addition, recent findings show th at, in opposite to the
finding reported by Cohen and Stewart (1982), developmental effects can
indeed be obtained for SPTs: Ratner and Hill (1991) found th a t recall of
SPTs was higher for fourth graders (mean age = 9 years and 10 months)
than for first graders (mean age = 6 years and 11 months).
The presence of aging effects and developmental effects on SPT recall has
implications for Cohen's explanation of differences between SPT and VT
recall in term s of involvement of strategy. It has furthermore been shown
th a t recall of the verbal instructions in the SPT task is negatively affected
by division of attention (Bäckman et al., 1986, 1991). To the extent th a t
24
im pairm ent in recall following dual-task performance is a characteristic
feature of strategic memory tasks (Hasher & Zacks, 1979), this adds to the
evidence against the notion th a t SPTs are encoded without the use of
strategy. Nevertheless, developmental effects, effects of aging, and effects
of dual-task performance appear to be somewhat less pronounced for
SPTs than for VTs (see e.g., Study II). Therefore, it cannot be ruled out
th a t the SPT task, on the continuum progressing from autom atic to
effortful memory operations proposed by H asher and Zacks (1979), is
fu rth er towards the autom atic end th an are VTs. Alternatively, the
diminished effects in the case of SPTs can be seen as supporting the dual­
conception hypothesis suggested by Bäckman et al. (1991), stating th a t
encoding of the verbal task component in SPTs is effortful and encoding of
the physical features (e.g., color and weight) is relatively automatic.
Taken together, it is argued th a t the existing evidence is too meagre to
w arrant introduction of new laws of memory. Cohen (1981) stated th a t it
may be advisable to use apparent memory law violations in the first
instance as suggesting reappraisal rather than abandonment of existing
laws (for a case of abandonment, see Nilsson & Bäckman, 1989a). At
present, I belive th a t neither reappraisal nor abandonment is called for.
Theoretical explanations
The resu lts presented in the empirical section of the thesis have
implications for aspects of several previously proposed explanations of the
SPT effect. The finding of a higher memory performance for VTs
involving real objects than standard VTs, and the disappearance of the
SPT effect when real objects were presented in VTs, show th a t objects do
indeed enrich the encoding. However, according to a richness of encoding
view (e.g., Bäckman et al., 1986), m anipulation of objects should further
enrich the encoding, but this was not found to be the case; SPTs and VTs
involving real objects were remembered to the same extent. Moreover, if
the multimodal aspects of objects are critical for the SPT effect, it is
expected th a t the SPT effect should be smaller for SPTs not involving
extra-environmental objects than for SPTs involving such objects. This
was not found to hold true. Thus, the sensory richness of objects does not
seem to be critical for the SPT-effect; a conclusion th a t also has been
acknowledged by others (cf., Engelkamp & Cohen, 1991).
25
Although the object component does not seem to be critical for the SPT
effect, the results from Study III strongly suggest th a t objects function as
effective retrieval cues, and th a t they, particularly in the absence of the
motoric component, can serve to enrich the encoding. This p attern of
results can be seen as a possible explanation of the discrepant findings
concerning the role of physical enactment by the subjects. The Engelkamp
group has repeatedly found a superiority in memory performance of SPTs
over EPTs, whereas Cohen has found non-significant differences between
these conditions. Real objects are used by Cohen but not by Engelkamp,
and in the absence of enactment on the part of the subject, this difference
in procedure may have a strong effect on memory performance. That is,
rather than assuming th a t a motor system is activated by SPTs but not by
EPTs (cf., Engelkamp & Zimmer, 1985), I belive th a t the difference in
memory performance following SPT vs EPT encoding is dependent on how
supportive the encoding environment is. When real objects are used, the
difference between SPT and EPT conditions in term s of encoding support
is small; when real objects are not used, the difference is increased and
physical enactment by the subject is critical for a high performance.
Furtherm ore, the finding th a t presentation of VTs along with external
objects gave as high memory performance as did actual enactment of the
action phrases has implications for the question of the importance of the
m otor component. Admittedly, it is possible th a t subjects im agined
performing the tasks when they were presented with the objects and the
action phrases, and thereby encoded motor aspects (cf., Bäckman, 1985).
Given such an assumption, this finding appears to be consistent with
explanations in which the motor component holds a salient position.
However, it should be noted th a t the subjects were not in stru cted to
imagine performing the actions. Therefore, it is also possible to interpret
this lack of effect of enactment in accordance with the approach proposed
by H elstrup (1987). That is, adding motor cues to the encoding was not
necessary; the available memory cues (the objects) were sufficient. Such
an interpretation implies th a t there is nothing special about motor cues,
which seems to be in p articular disagreem ent w ith the position of
Engelkamp and Zimmer who consider the motor component to be of
particular importance (e.g., Engelkamp & Zimmer, 1985; b u t see Zimmer
& Engelkamp, 1989b).
26
I would like to argue in favour of a position in which the motor component
can be described as "special, but not so special". Specifically, I do not
think th a t there are qualitative differences between SPTs on one hand,
and EPTs, VTs including real objects, and imagined actions on the other
hand. I am of the impression th a t these different encoding manipulations
can be explained in terms of their effect on the memory trace of an event,
and I belive th a t they affect traces in a similar manner. However, there
may be quantitative differences, in term s of memorability, between the
traces resulting from these various encoding manipulations. W hether or
not these differences show up should depend on the difficulty of the task
(cf., Nyberg, Nilsson, & Bäckman, 1992), and on subject characteristics
(cf., Bäckman, 1985; Bäckman & Nilsson, 1985). In the next section, a
model is proposed in which it is described how enactm ent affects the
memory trace of an event.
Finally, the study of the effect of the SPT m anipulation on im plicit
memory performance (Study IV) provided no support for the hypothesis
th a t SPTs add conceptual information, as well as motoric information, to
the memory trace (see Nilsson & Craik, 1990). Quite opposite, the data
suggested th a t the basis for the generation effect and the SPT effect in free
recall is not the same. It has been shown th at generation in terms of letter
reversal leads to deeper semantic processing as compared to reading, and
the generation effect is believed to be based on an integrated conceptual
representation in semantic memory (Gardiner, Gregg, & Hampton, 1988).
Activation of semantic memory representations is believed to underlie
conceptual priming (Tulving & Schacter, 1990), and a generation effect on
category association is therefore the to-be-expected finding. On the
contrary, the lack of an SPT effect on category association implies th a t
enactm ent does not lead to deeper conceptual processing, thereby
indicating th a t the SPT m anipulation does not work as a sem antic
orienting task. Thus, given th a t enactment does not increase the depth of
processing, an explanation of the SPT effect has to be based on other
terms. Klein and Saltz (1976) have shown th a t semantic enrichment can
increase memory performance w ithin the semantic domain, and in a
similar vein Nyberg and Nilsson (1992) offered an explanation of the SPT
effect in term s of motoric enrichment. In closing, this explanation will be
further developed in a tentative model.
27
A d istinctiveness m odel
Analysis of the effect of encoding operations m ust involve consideration of
the nature of the memory test (Eysenck, 1979; H unt & Einstein, 1981;
Jacoby & Craik, 1979). The literature suggests th at the SPT effect on cuedrecall performance generally exceeds the enactment effect on free recall
and recognition: Saltz (1988), based on examination of various data sets,
provided the impression th a t enactment leads to much greater facilitation
of memory on cued recall than on free recall. Svensson and Nilsson (1989)
reported data showing a stronger SPT effect on recall of nouns using the
verbs as cue, than on recognition of the nouns. Similarly, Nyberg (1992)
reported a significant SPT effect on recall of verbs using the nouns as cue,
but a nonsignificant SPT effect on recognition of the verbs. Finally, there
is some evidence th a t the SPT effect is stronger on free recall th an on
recognition (Nilsson & Craik, 1990; but see Mohr, Engelkamp, & Zimmer,
1989). In all, this shows th a t enactment improves recall as much as it
improves recognition memory, which in tu rn has im plications for
explanation of the SPT effect (cf., Tulving, 1979). This is because encoding
operations mainly enhancing item-specific processing has the strongest
effect on recognition memory, whereas encoding operations improving
relational processing has the greatest effect on recall. Both types of
processing combine to produce optimal recall (Hunt & Einstein, 1981), and
it is proposed in this concluding section th a t enactm ent improves itemspecific processing as well as relational processing, and th a t these forms
of processing, in combination, serve to increase the distinctiveness of the
memory trace (cf., H unt & Einstein, 1981, p. 511).
Before presenting the support for the view th a t enactment improves both
item-specific and relational processing, it is necessary to define the
c u rre n t conceptualization of th e key term s m em ory trace and
d istinctiveness. A memory trace is here considered as consisting of a
variety of attributes (e.g., Bower, 1967; Craik & Tulving, 1975; Underwood,
1979); no assumptions are made regarding the way the traces are stored
(i.e., w hether the traces are localized or distributed; cf., Estes, 1991). The
attributes may be ones th a t are chosen by subjects at encoding (such as
associations generated by strategical processing or visual images), but
some attributes are also an unavoidable p art of the encoding situation
(such as m odality of in p u t and phonemic recoding during input).
28
Distinctiveness is used to describe the similarity of the product of encoding
operations in terms of a memory trace to other traces (Craik, 1979), and a
highly distinctive memory trace is a trace which shares few features with
other to-be-remembered events.
The assumption th a t enactment increases distinctiveness by the addition
of item-specific information (information highly specific to each input
event) appears to be consistent with most previous explanations of the SPT
effect. For example, Engelkamp and colleagues have explained the SPT
effect by the fact th a t enactment activates motor programs which yield
excellent item-specific information and become a part of the memory trace
(e.g., Engelkamp, 1990; Zimmer & Engelkamp, 1989b). Bäckman and
Nilsson (e.g., Bäckman et al., 1986) have argued that, in addition to verbal
information, information about the motor actions (including features of
color, texture, and shape) can be stored in the SPT task, and this
additional information is believed to facilitate memory. H elstrup (1986)
has favoured an "attribute-bundle memory conception", in which motor
attributes are added to other attributes in the memory trace. Saltz (e.g.,
Saltz & Donnenwerth-Nolan, 1981) has proposed th at enactment results in
the storage of motoric images which leads to a more specific registration.
Finally, Baddeley (1990) has explained the effect of enactment on memory
performance in term s of the addition of motor cues which produces
enhanced memory trace discriminability.
Thus, most explanations of the SPT effect are at least broadly consistent
w ith the first assumption in the present model th a t enactm ent adds
specific information to the memory trace - information th a t is not added
in VTs. In line w ith many previous w riters, we have suggested the
motoric component as the source of the added information (Nyberg &
Nilsson, 1992). Specifically, enactment during encoding of action phrases
is believed to result in storage of some sort of motoric images (cf., Saltz &
Donnenwerth-Nolan, 1981), and this attribute (the motoric image) is
thereby an "unavoidable part" of the encoding situation (cf., Underwood,
1979). The encoding of motoric images should result in distinctive traces,
and a distinctiveness interpretation is further supported by the finding in
Study II of a smaller drop in performance between IFR and FFR for SPTs
than for VTs. This finding was explained by SPTs being less susceptible to
proactive interference th an VTs, and it has been argued th a t more
29
distinct memory traces are less affected by interference (see Bradshaw &
Anderson, 1982; Saltz & Donnenwerth-Nolan, 1981; Wickelgren, 1973).
To sum up so far, it has been suggested th a t enactment adds item-specific
inform ation to the memory traces, which makes these traces more
discriminable than traces resulting from verbal encoding. However, this
type of item-specific information is similar to what Underwood (1969) has
called "discriminative attributes of memory", and should mainly serve to
improve recognition memory (see also Eysenck, 1979). As discussed above,
the SPT effect appears to be, a t least, as great in recall as in recognition,
and some sort of "retrieval attrib u tes" (Underwood, 1969) seems
w arran ted to explain the strong effect of enactm ent on recall
performance. This brings us to the second assum ption in the present
model; th a t enactment improves relational processing.
Recall performance is believed to rely to a high extent on relational
inform ation, which is seen as having a generative function (H unt &
Einstein, 1981). Several different types of relational information can be
identified in the literature. Relational processing as discussed by H unt
and Einstein (1981) refers to the encoding of similarities among a class of
events. H irshm an & Bjork (1988), in discussing the role of relational
processing for the generation effect, used the term relational to denote the
relation between stimulus and response. Engelkamp and co-workers (for
a review, see Engelkamp, 1990) have considered both of these forms of
relational information in explaining the effect of enactment:
Engelkamp and Zimmer distinguish between categorical integration and
integration of unrelated events. Categorical integration is believed to be
independent of enactment, a finding supported by sim ilar am ounts of
categorical clustering for SPTs and VTs (e.g., Zimmer, 1991; Zimmer &
Engelkamp, 1989a,b). The second form of integration is assumed to be
h in dered by enactment. This assumption is supported by a study by
Engelkamp (1986) in which cued recall of performed verb pairs was
shown to be poorer than free recall of the same word pairs. Helstrup (1989,
1991) has shown th at if subjects are instructed to try to integrate the verb
pairs (or noun pairs), enactm ent helps memory performance. However,
Engelkamp has argued th a t under sta n d a rd SPT instructions, pair
integration is actually hindered by enactment (e.g., Engelkamp, Mohr, &
Zimmer, 1991).
30
The second assumption in the present model, thus, appears to contradict
the assum ptions in the theory proposed by Engelkamp and his co­
workers. Below, I will present the empirical evidence th a t have led me to
propose th a t enactment improves relational processing.
In contrary to the findings by Zimmer (Zimmer, 1991; Zimmer &
Engelkamp, 1989a), Bäckman has reported th a t SPTs benefit more form
the relational list structure than do VTs (Bäckman et al., 1986). Bäckman
et al. found higher levels of clustering for SPTs than for VTs, and a high
degree of clustering indicates th a t good relational encoding of the list
structure has been achieved. It has been suggested th a t this discrepancy
in results is due to the fact th a t SPTs with real objects were used in the
Bäckman et al. study, whereas symbolically performed SPTs are used in
the paradigm utilised by Zimmer and Engelkamp (e.g., Zimmer &
Engelkamp, 1989). Support for the suggestion th at the object component is
the source of this form of relational information is provided by the high
recall performance for VTs when the corresponding objects were shown,
and also by the finding of markedly higher organizational scores on the
object dimension than on the motor dimension, reported in the empirical
section of this thesis (Study III). Furtherm ore, given th a t the object
component improves this form of relational processing, this may provide
an explanation to the conflicting data concerning the magnitude of the
SPT effect on recall versus recognition: Engelkamp and his co-workers
have found a greater SPT effect on recognition than on recall (Mohr et al.,
1989), whereas Nilsson and associates have reported findings of a more
pronounced SPT effect on recall th an on recognition (Nilsson & Craik,
1990; Nyberg, 1992; Svensson & Nilsson, 1989). The Engelkamp group has
used symbolically performed actions, whereas the Nilsson group has used
SPTs involving real objects. Thus, a more precise formulation might be
th a t the SPT procedure used in our laboratory and by Cohen (including
the involvem ent of real objects) enhances encoding of inform ation
common to the input events.
Turning to the second form of relational processing (between stim ulus
and response), Engelkamp has, as noted above, based his conclusion th a t
improved relational processing is not the basis for the SPT effect on
studies of pair-relational encoding of unrelated actions (e.g., Engelkamp,
1986). I will not dwell on w hether enactm ent improves or hinders
31
integration of this type of m aterials (interested readers are referred to
Engelkamp et al., 1991 and Helstrup, 1991), because, in agreement with
Saltz (1988), I belive th a t this is the wrong relation to consider if one
attem pts to explain the SPT effect. Saltz argues th at the integration to be
sought for is not between two unrelated actions, as in the paradigm used
by Engelkamp, but rather integration within a sentence framework (i.e.,
betw een act and actor). If the la tte r type of integration is under
investigation, he argues, enactment is indeed helpful.
In line with Saltz, I assume th a t enactm ent strengthens the relation
between verb and noun. A strong integration between verbs and nouns
following enactm ent should enhance cued-recall performance due to
distinctive connections between cues and traces (cf., Lockhart & Craik,
1990). Similarly, a strong integration between verb and noun should
reduce the search space, thereby facilitating free recall as well as cued
recall. This view, th a t enactm ent strengthens the integration between
verb and noun, is also supported by recent empirical findings from our
own laboratory (Kormi-Nouri & Nilsson, 1993).
Thus, according to the proposed framework the enactm ent effect is
explained in term s of distinctiveness. Enactment is seen as increasing the
distinctiveness of the memory trace by improving item-specific as well as
relational processing. Relational processing includes both categorical
integration and event integration. The assumption th a t item-specific and
re la tio n a l inform ation, in com bination, serve to in crease th e
distinctiveness of the memory trace is consistent with the view advanced
by H unt and Einstein (1981), and this explanation of the SPT effect
em braces m any em pirical findings reported in the lite ra tu re . In
p articu la r, by assum ing th a t enactm ent im proves both forms of
processing it is possible to explain the strong effect of enactment on tests of
recall as well as on recognition, and such consideration of the
compatibility between trace and cue information is necessary in analyses
of the workings of encoding manipulations (cf., Tulving, 1979). It should
be pointed out, though, th a t a few aspects of the above proposed model
have to be corroborated by further empirical work. The most critical test of
the model is probably to examine the validity of the assumption th a t
enactm ent improves relational processing. Until such a te st has been
performed, the conclusion th a t encoding of relational and item-specific
information causes the enactment effect has to be tentative.
32
Concluding rem arks
The studies presented have highlighted sim ilarities ra th e r th a n
differences between memory for enacted and nonenacted events. Based on
a discussion of possible memory laws related to acquisition, retention, and
retrieval, it was concluded th at the basic laws for recall of SPTs and VTs
are the same. This conclusion is at odds with some previous proposals
(see especially Nilsson & Bäckman, 1989a), and may reflect the author's
bias towards emphasizing regularities rath e r th a t anomalies. F uture
research will no doubt tell w hether this conclusion holds true, or if the
basic laws of enacted and nonenacted memory really are fundamentally
different.
In addition, a tentative model was suggested in which the enactm ent
effect is explained in term s of the addition of item-specific and relational
information. It was hypothesized th a t these forms of information, in
combination, serve to increase the distinctiveness of memory traces.
Although the suggested distinctiveness model share some features with
previously proposed explanations of the SPT effect, the model contains
quite a large number of novel assumptions. An im portant task for future
research will therefore be to put these assumptions under experimental
scrutiny.
In closing, the concept of distinctiveness has held a central position in
explanations of the effect of encoding operations on memory performance
(cf., Jacoby & Craik, 1979), and it is believed th at a distinctive trace stands
out from traces of other events and is therefore more retrievable. The
memory traces appear to stand out very strongly following enactment,
suggesting th a t motoric information has high contrastive value (Jacoby &
Craik, 1979), but still this memory phenomenon seems possible to explain
by using traditional memory concepts. To me, such an explanation,
avoiding the invention of new systems or mechanisms, is appealing.
33
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