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MEMORY, 2008, 16 (4), 329340
Phonological and semantic strategies in
immediate serial recall
Guillermo Campoy
University of Murcia, Spain
Alan Baddeley
University of York, UK
It has been suggested that certain theoretically important anomalous results in the area of verbal shortterm memory could be attributable to differences in strategy. However there are relatively few studies
that investigate strategy directly. We describe four experiments, each involving the immediate serial
recall of word sequences under baseline control conditions, or preceded by instruction to use a
phonological or semantic strategy. Two experiments varied phonological similarity at a presentation rate
of one item every 1 or 2 seconds. Both the control and the phonologically instructed group showed clear
effects of similarity at both presentation rates, whereas these were largely absent under semantic
encoding conditions. Two further experiments manipulated word length at the same two rates. The
phonologically instructed groups showed clear effects at both rates, the control group showed a clear
effect at the rapid rate which diminished with the slower presentation, while the semantically instructed
group showed a relatively weak effect at the rate of one item per second, and a significant reverse effect
with slower presentation. The latter finding is interpreted in terms of fortuitous differences in inter-item
rated associability between the two otherwise matched word pools, reinforcing our conclusion that the
semantically instructed group were indeed encoding semantically. Implications for controlling strategy by
instruction are discussed.
Verbal short-term memory (STM) has traditionally been conceived as relying on the maintenance of phonological representations. Evidence
supporting this view emerged first from the
observation by Conrad (1964) that errors in
immediate recall of consonants tended to be
similar in sound to the correct item (e.g.,
misrecalling V instead of P), even when the
stimuli had been presented visually. Congruently
with this, Conrad and Hull (1964) showed that
lists of letters similar in sound (e.g., V, C, P, D,
T) were harder to recall than lists of dissimilar
letters (e.g., K, Z, W, R, Y), which was explained
in terms of the greater difficulty of discriminating among similar phonological traces. On the
basis of these and similar results, various memory models have included the idea that verbal
material is phonologically coded in STM. According to the working memory model, for
example, the short-term maintenance of verbal
material is mainly accomplished by the phonological loop, which comprises a phonological
store where phonological traces are maintained
and a control process of subvocal rehearsal that
refreshes traces and counteracts decay (Baddeley, 2007; Burgess & Hitch, 1999).
Address correspondence to: Guillermo Campoy, Departamento de Psicologı́a Básica y Metodologı́a, Universidad de Murcia,
Campus de Espinardo, Apartado de correos 4021, 30080 Murcia, Spain. E-mail: [email protected]
We thank Alice F. Healy, Jean Saint-Aubin, Gerry Tehan, and Ian Neath for constructive comments on earlier versions of this
article. We also thank Mercedes Cortes for her help in stimulus recording, and Lucia Colodro and Beatriz Cuevas for their assistance
in data collection.
# 2008 Psychology Press, an imprint of the Taylor & Francis Group, an Informa business
http://www.psypress.com/memory
DOI:10.1080/09658210701867302
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330
CAMPOY AND BADDELEY
Even though it seems clear that phonological
coding plays a major role in verbal STM tasks
involving the immediate serial recall of digits or
unrelated words, it is also the case that immediate
recall of verbal material can benefit from the
short-term maintenance of other kinds of information, especially semantic. Studies of the immediate recall of sentences, for example, have
shown that participants can recall many more
words from sentences than from lists of unrelated
words (Brener, 1940). There are a number of
factors that could contribute to this phenomenon,
including syntactic constraints and lexically based
sequential redundancy. However, it seems likely
that sentence superiority is in part a consequence
of participants being able to maintain the overall
meaning of the sentence and use this information
at recall. In keeping with this idea, Jefferies,
Lambon Ralph, and Baddeley (2004) showed
that, whereas phonological errors (e.g., misrecalling rut instead of rug) were more common than
semantic errors in word-list recall, semantic errors
(e.g., misrecalling carpet instead of rug) were
more frequent in sentence recall.
Although sentence recall is probably especially
propitious for the participation of semantic information, there are a number of findings that
suggest that the maintenance of semantic information may also play a role in the immediate
serial recall of unrelated words. Some such
evidence comes from studies showing poorer
recall for words with a low semantic content
(e.g., articles, prepositions, conjunctions) than for
more meaningful words such as adjectives and
nouns (Caza & Belleville, 1999; Tehan & Humphreys, 1988; see, however, Bourassa & Besner,
1994). This finding could be attributed to the fact
that, although recall relies mainly on phonological traces, participants are able to encode and use
semantic information to improve performance,
with semantically richer words gaining a greater
advantage. Further evidence comes from studies
that manipulate semantic similarity. In an early
study, Baddeley (1966) examined the immediate
serial recall of five-word lists drawn from a set of
eight phonological similar words, from a set of
eight adjectives with similar meanings, or from a
set of eight control words. Results showed a clear
effect of phonological similarity, but also a small
but significant effect of semantic similarity (worse
recall of semantically similar items). This result
suggests a contribution to recall from both
phonological and semantic encoding, with similar
words resulting in less distinctive traces and
therefore poorer recall. A subsequent study by
Baddeley and Levy (1971) showed that semantic
coding could be induced in immediate serial
recall of six-word sequences comprising three
nounadjective pairs, provided the pairs were
semantically compatible (e.g., priestdevout), an
effect that was eliminated when the pairs were
made semantically similar to other pairs within
the list (e.g., bishoppious). A further study
(Baddeley & Ecob, 1970) using semantically
compatible or incompatible triplets (e.g., my fine
wine vs wine my fine) found effects of both
phonological and semantic similarity, with acoustic similarity impairing performance on immediate test, and effects of semantic similarity
predominating after a delay*results that they
interpreted as suggesting simultaneous encoding
of both phonological and semantic features.
More recently, Poirier and Saint-Aubin (1995);
Saint-Aubin & Poirier, 1999; Saint-Aubin, Ouellette, & Poirier, 2005) have found effects of
semantic similarity in a number of experiments
in which similarity was manipulated by presenting
words from the same semantic category (e.g.,
horse, bull, goat, mare, pig, cow) or from different
categories. Overall, semantic similarity led to a
better recall in these studies,1 which was explained by an extended version of the redintegration hypothesis. According to the redintegration
hypothesis (Hulme, Maughan, & Brown, 1991;
Schweickert, 1993), short-term recall involves the
participation of reconstructive mechanisms by
which partially degraded phonological traces are
redintegrated on the basis of long-term knowledge
about the constituent words. In their extended
version of the hypothesis, Poirier and Saint-Aubin
suggested that semantic information improves
redintegration accuracy by providing an additional cue that delimits the number of suitable
candidates in long-term memory (Poirier &
Saint-Aubin, 1995; Saint-Aubin & Poirier, 1999).
1
This advantage for lists of semantically similar lists could
be seen as conflicting with the results obtained by Baddeley
(1966), who found worse recall for lists of similar words.
However, this discrepancy is easily explained by relevant
procedural differences. Semantic similarity in the studies by
Saint-Aubin and Poirier was found to have a large beneficial
effect on item recall, but also a slight detrimental effect on
order recall (Saint-Aubin et al., 2005). The negative effect
found by Baddeley (1966) can be explained by the fact that, in
contrast to Saint-Aubin and Poirier, Baddeley used closed sets
of stimuli, which were, moreover, displayed during recall. It
seems clear that performance in this situation was a product of
order rather than item recall, with the consequence of worse
recall for similar lists.
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STRATEGIES AND IMMEDIATE SERIAL RECALL
Consider, for example, that the phonological
representation of the word cat has lost the last
phoneme. In this situation, the redintegration
process could lead to error because the remaining
trace would fit with a number of incorrect words
(cab, can, cache, cad, cash, cap, etc.). Stored
semantic information would be useful then to
pick the candidate whose meaning is consistent
with this semantic information. For Poirier and
Saint-Aubin, the advantage of similar word lists
would be a consequence of the fact that semantic
similarity results in a more recallable and efficient
semantic cue (Poirier & Saint-Aubin, 1995; SaintAubin & Poirier, 1999). Again, findings support
the idea that participants in STM tasks encode
semantic information and employ this information at recall.
Whereas there is broad agreement that semantic coding may play a role in immediate serial
verbal recall, there is less agreement on how to
interpret it. One possibility is to attribute it to the
influence of long-term memory, the view initially
taken by Baddeley (1972). Within the multicomponent working memory framework, Baddeley (2000, 2007) has subsequently proposed that
an additional component, the episodic buffer,
provides a link between long-term and working
memory, accounting for the short-term effects of
semantic coding. Another approach is to propose
a separate semantic STM (e.g., Martin, 2005), a
view derived from studies of brain-damaged
patients (Freedman & Martin, 2001; Hanten &
Martin, 2000; Majerus, Van der Linden, Poncelet,
& Metz-Lutz, 2004; Martin & He, 2004; Martin &
Romani, 1994; Martin, Shelton, & Yaffee, 1994;
Romani & Martin, 1999), from neuroimaging
dissociations (Martin, Wu, Jackson, Freedman,
& Lesch, 2003; Shivde & Thompson-Schill, 2004),
and from behavioural data (Haarman, Ashling,
Davelaar, & Usher, 2005; Haarman, Davelaar, &
Usher, 2003; Haarman & Usher, 2001).
Regardless of these different conceptions and
their theoretical consequences, the fact that
verbal STM can be partially supported by stored
semantic information is a potential source of
important interpretative problems in verbal
STM experiments, with different investigators
obtaining conflicting results. The reason for this
is that, although the use of a phonological
strategy for recalling short sequences of verbal
items may predominate, such a strategy may
lose ground in favour of other strategies under
certain conditions (Logie, Della Sala, Laiacona,
Chalmers, & Wynn, 1996).
331
There are a number of instances of theoretically important results in which major inconsistencies appear to have resulted from switching
between phonological encoding and another
strategy, probably semantic. One instance concerns the claim that poor beginning readers fail to
show the characteristic phonological similarity
effect in verbal STM, which Liberman and
colleagues (Liberman, Mann, Shankweiler, &
Werfelman, 1982; Mann, Liberman, & Shankweiler, 1980) suggest might reflect a general failure of
poor readers to encode visual material phonologically, providing a possible cause of their reading
deficit. Subsequent research suggested that poor
readers do encode phonologically at shorter list
lengths, only failing to show a phonological
similarity effect when list length greatly exceeded
their memory span, which is typically shorter than
that of good readers (Hall, Wilson, Humphries,
Tinzmann, & Bowyer, 1983; Johnston, 1982). This
result is generally attributed to the abandonment
of a phonological strategy (Baddeley, 2007; Johnston, 1982). Such an interpretation has also been
offered for data from adults, whereby phonological variables that are present at short list lengths
may not be found with longer lists, particularly
when other variables such as irrelevant speech or
articulatory suppression are involved. For example, Salamé and Baddeley (1986) studied the
combined effects of phonological similarity and
irrelevant speech across a range of list lengths,
finding additive effects of both variables that
disappeared as list length increased, suggesting
the absence of phonological coding with longer
lists. A similar interaction between phonological
coding and list length occurs when auditory
presentation is used under articulatory suppression (Baddeley & Larsen, 2007; Jones, Macken, &
Nicholls, 2004), resulting in a claim by Jones et al.
that their data are inconsistent with the concept
of a short-term phonological store. However,
Baddeley and Larsen (2007) suggest that the
results of Jones et al. simply reflect the abandonment of phonological coding as level of difficulty
increases.
Preliminary empirical evidence for the potential importance of strategy comes from Logie
et al. (1996). In this study, participants were
interviewed after a series of verbal STM tasks in
order to determine the strategies that they had
employed. Results revealed that participants
classified as using a semantic strategy showed
weaker phonological effects (phonological similarity and word length) than the great majority of
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CAMPOY AND BADDELEY
participants who reported adopting a phonological strategy. A more direct approach to strategy
was taken by Hanley and Bakopoulou (2003),
Experiment 2), in a study involving the immediate serial recall of phonologically similar or
dissimilar letter sequences. They left one group of
participants free to select any strategy, instructed
a second group to encode phonologically, while a
third group was asked to use each item as the
initial letter of a word, instructing them to link
the words to form a sentence. They obtained the
standard phonological similarity effect in the
baseline group, a more marked phonological
similarity effect when phonological coding was
encouraged, and an absence of a phonological similarity effect under their lexical-semantic
instructions.
The experiments that follow aim to build
on this observation in the hope of developing
methods within which strategy can be controlled
and manipulated, so as to facilitate a resolution of
controversies based on the possibility of strategy
switching. We chose to study the consequences of
attempting to induce a phonological or semantic
strategy on the presence or absence in serial
verbal STM of two well-established effects,
the previously described phonological similarity
effect, and the word-length effect, the finding that
immediate recall is worse for lists of long words
than for short words (Baddeley, Thomson, &
Buchanan, 1975).
The precise mechanism underlying the word
length effect remains a matter of controversy.
According to the working memory model, the
effect is a consequence of a faster rehearsal rate
for short words, so that a larger number of short
words can be reactivated before they are lost
because of decay (Baddeley, 1986; Burgess &
Hitch, 1999; Mueller, Seymour, Kieras & Mier,
2003). Other authors, however, have suggested
that the word-length effect is a result of differences in the phonological complexity of the
items (Campoy, 2008; Caplan, Rochon, & Waters,
1992; Hulme, Suprenant, Bireta, Stuart, & Neath,
2004; Romani, McAlpine, Olson, Tsouknida, &
Martin, 2005; Service, 1998), with more complex
words having been proposed to result in less
distinctive traces (Hulme et al., 2004; Hulme et
al., 2006). Despite the differences, these explanations attribute the effect to phonological factors
rather than to semantic coding, a view that is
consistent with the self-report data collected by
Logie et al. (1996). It could be predicted, therefore, that the induction of a semantic strategy
would result in the reduction of the word length
effect.
EXPERIMENT 1
In Experiment 1 we presented lists of five words
for immediate serial recall. Three conditions were
studied: a control condition in which no strategy
was suggested, a second condition in which
participants were instructed to employ a semantic
strategy (‘‘Try to think of the word meanings and
link them’’), and a third phonological strategy
condition (‘‘Try to maintain and rehearse the
word sounds’’). Experiment 1 investigated the
effect of these strategies on the phonological
similarity effect.
Method
Participants. A total of 60 undergraduates from
the University of Murcia were tested, 20 in each
strategy condition.
Stimuli. Two sets of Spanish words were used,
one comprising eight phonologically similar
nouns and the other containing eight phonologically dissimilar nouns (see Appendix A). The
word sets were individually matched for word
frequency, familiarity, imageability, and concreteness using the LEXESP database (Sebastián,
Martı́, Carreiras, & Cuetos, 2000). All the words
comprised two consonantvowel syllables (two
phonemes per syllable) with the stress on the
penultimate syllable. Words in the similar set
shared at least the two vocalic sounds. Phonological similarity in the dissimilar set was minimised
by ensuring that no words shared more than
one phoneme in the same position. A computer program generated by E-Prime (Schneider,
Eschman, & Zuccolotto, 2002) was used for
stimulus presentation and response storage.
Procedure. Participants were tested individually in a sound-attenuated booth. The experiment
consisted of three blocks of 16 trials, 8 trials with
phonologically similar words and another 8 trials
with dissimilar words. The order of presentation
of similar and dissimilar lists within a block was
determined at random. Lists were constructed by
selecting words from the specific set at random,
with the constraint that every word appeared in
five trials per block, once in each of the five
possible positions of the lists. Four practice trials
were presented before the experimental trials.
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STRATEGIES AND IMMEDIATE SERIAL RECALL
Instructions about the strategy to be employed
were given after the second practice trial, once
participants were familiar with the procedure.
Participants were told that the objective of the
experiment was to test different memory strategies and that it was therefore crucial that they
used the specified strategy even though they
thought that a different strategy could lead to
better performance. They were reminded of
strategy instructions before each of the three trial
blocks.
The sequence of events in each trial was the
following. First, a row of dashes appeared indicating that a mouse button had to be pressed to
initiate the trial. One second after the mouse
click, a plus sign was presented in the centre of
the screen for 1 second, followed by a five-word
list. Items were presented at a rate of one item
per second (950 ms on, 50 ms off). After the list
presentation, the 16 experimental stimuli appeared on the computer screen and participants
employed the mouse to click on the five list words
in their presentation order (clicked words appeared in bold). Participants were instructed to
click on a question mark in place of any word
they did not remember. A restart button labelled
‘‘BBB’’ could be used in case of error. When
they had finished list reconstruction, they were
required to press an unlabelled black button. The
basic screen configuration during list reconstruction is illustrated in Figure 1. The arrangement of
the 16 experimental stimuli within this configuration was established at random at the beginning
of the experiment for each participant.
333
Results and discussion
Raw data were scored according to a strict serial
recall criterion, by which a response was counted
as correct when the right item was recalled in the
correct position. The mean percentage correct
recall is presented in Table 1. A 2 (word
similarity)3 (induced strategy) mixed analysis
of variance revealed a main effect of word
similarity, F(1, 57)58.90; MSe58.87; pB.01;
h2 p 0.51, with the phonologically dissimilar
words being better recalled. The main effect of
strategy was not significant, F(2, 57) 1.88;
MSe322.90; p.16; h2 p 0.06, but there was
a significant strategy by similarity interaction,
F(2, 57)6.48; MSe58.87; pB.01; h2 p 0.19.
Further analysis indicated a significant effect of
phonological similarity for the uninstructed control group, F(1, 57)30.01; MSe117.74; pB.01;
h2 0.34, and for the group instructed to use
phonological coding, F(1, 57) 39.51; MSe 117.74; pB.01; h2 0.41, but not for the group
instructed to encode semantically, F(1, 57)2.34;
MSe117.74; p.13; h2 0.04. When similar
and different sequences were analysed separately
to investigate the interaction further, there
proved to be no difference between the three
strategy groups on dissimilar items, F(2, 57)B1;
h2 0.00, whereas the groups did differ on similar
word performance, F(2, 57)5.00; MSe193.04;
p.01; h2 0.15, with the semantic group showing significantly better performance than either
the control or phonological groups: respectively,
F(1, 57)7.77 and 7.20; MSe193.04; pB.02;
h2 0.12 and 0.11, which did not differ.
Some idea of the consistency of the phonological similarity effect can be obtained by the
number of participants showing an overall effect (cf. Logie et al, 1996). This was 18 out of 20
for the control group, 20 out of 20 for the
TABLE 1
Experiment 1
Induced strategy
Semantic
Phonological
Control
Dissimilar words 70.37 (14.02) 69.67 (13.54) 68.17 (13.93)
Similar words
66.67 (15.54) 54.42 (12.41) 54.88 (13.55)
Difference
3.71 (11.12) 15.25 (8.53) 13.29 (12.52)
Figure 1. Example of screen configuration during list reconstruction.
Means (and standard deviations) of the percentages of
correct responses as a function of phonological similarity and
induced strategy in Experiment 1.
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CAMPOY AND BADDELEY
phonological group, and 12 out of 20 for the
semantic group.
The results of Experiment 1 are straightforward. Both the control and phonological strategy
groups showed the expected effect of phonological similarity, while the semantic strategy group
did not. Strategy appeared to have no effect on
retention of dissimilar words, but semantic coding
appeared to protect participants from the effects
of phonological similarity, leading to enhanced
performance on these items. Experiment 2 extends our investigation of strategy effects to their
influence on word length.
EXPERIMENT 2
Method
Participants. Participants were 75 undergraduates from the University of Murcia, 25 in
each strategy condition.
Stimuli and procedure. Two sets of Spanish
words were used, one comprising eight disyllabic
nouns and the other containing eight trisyllabic
nouns (see Appendix B). The word sets were
matched for word frequency, familiarity, imageability, and concreteness using the LEXESP
database (Sebastián et al., 2000). All the words
consisted of consonantvowel syllables with the
stress on the penultimate syllable. Phonological
similarity was minimised by ensuring that no two
words from a set shared a syllable or more than
any two phonemes in the same position. Procedure was the same as in Experiment 1.
Results and discussion
Table 2 shows the mean percentage of items
correctly recalled. A 3 (strategy)2 (word
length) ANOVA showed a main effect of length,
F(1, 72)41.15; MSe27.92; pB.01; h2 p 0.36,
no main effect of strategy, F(2, 72)B1; h2 p 0.02,
and a marginally significant interaction, F(2,
72)2.49; MSe27.92; p.09; h2 p 0.06, with
all three groups showing a significant overall
word length effect*for the phonological, control,
and semantic groups, F(1, 72)29.14, 11.79, and
5.19 respectively; MSe55.84; pB.04; h2 0.29,
0.14, and 0.07. The number of participants showing a word length effect was 23 out of 25 for the
phonological strategy group, 20 out of 25 for the
TABLE 2
Experiment 2
Induced strategy
Short words
Long words
Difference
Semantic
Phonological
Control
70.64 (14.92)
67.23 (13.78)
3.41 (7.90)
74.47 (13.94)
66.40 (15.12)
8.07 (6.60)
75.90 (15.65)
70.77 (14.18)
5.13 (7.85)
Means (and standard deviations) of the percentages of
correct responses as a function of word length and induced
strategy in Experiment 2.
control group, and 16 out of 25 for the semantically instructed group.
Despite this suggestion of reduced robustness
of the word length effect under semantic encoding instructions, we failed to observe the clear
interaction with strategy we found for phonological similarity. On the other hand, we clearly
could not assert the absence of such an effect with
any degree of conviction. We suspect that one
problem with Experiment 2 might be that of
processing the longer words at the rapid one per
second rate employed. We therefore decided to
replicate both studies at a rate of 2 seconds per
word, which we felt would make it easier for
participants to perform the somewhat complex
recoding required for the semantic strategy (see
Shulman, 1970, 1971). Experiment 3, therefore,
examines the effect of phonological similarity as
in Experiment 1, except for rate of presentation,
which occurs at a slower rate of 2 seconds per
word.
EXPERIMENT 3
Method
Participants. Participants were 42 undergraduates from the University of Murcia, 14 in
each strategy condition.
Stimuli and procedure. Stimuli were the phonologically similar and dissimilar words used in
Experiment 1. The procedure was identical, except that lists were presented at a rate of one item
every 2 seconds (950 ms on, 1050 ms off).
Results and discussion
Means of percentage correct recall are shown in
Table 3. A 2 (word similarity)3 (induced
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STRATEGIES AND IMMEDIATE SERIAL RECALL
TABLE 3
Experiment 3
335
observe clearer effects of strategy at the slower
2-second rate.
Induced strategy
Semantic
Phonological
Control
EXPERIMENT 4
Dissimilar words 78.51 (10.89) 73.10 (16.43) 75.12 (12.67)
Similar words
76.73 (12.31) 61.61 (13.83) 65.12 (16.37)
Difference
1.79 (6.35) 11.49 (10.20) 10.00 (10.32)
Method
Means (and standard deviations) of the percentages of
correct responses as a function of phonological similarity and
induced strategy in Experiment 3.
Participants. Participants were 45 undergraduate volunteers from the University of Murcia,
15 in each strategy condition.
strategy) mixed analysis of variance revealed a
main effect of phonological similarity, F(1, 39)
30.23; MSe41.81; pB.01; hp 2 0.44, no effect
of strategy, F(2, 39)2.29; MSe344.84; p.11;
hp 2 0.11, and a significant interaction between
these two factors, F(2, 39)4.57; MSe41.81;
p.02; hp 2 0.19. This interaction was investigated by tests of simple main effects. These
showed significant effects of phonological similarity for the phonological and control groups,
respectively, F(1, 39)22.10 and 16.74; MSe
83.62; pB.01; h2 0.36 and 0.30, but not for the
semantic group, F(1, 39)B1; h2 0.01. As in
Experiment 1, therefore, results showed that the
induction of a semantic strategy resulted in the
elimination of the phonological similarity effect.
Again there was no effect of strategy with
dissimilar words, F(2, 39)B1; h2 0.03, but there
was a strategy effect for similar words, F(2, 39)
4.30; MSe203.70; p.02; h2 0.18. This effect
was due to the fact that similar words were better
recalled in the semantic group than in the
phonological and control groups, respectively,
F(1, 39)4.63 and 7.86; MSe203.70; pB.05;
h2 0.11 and 0.17, revealing that the elimination
of the phonologically similarity effect in the
semantic group was mainly due to better recall
of similar words.
A total of 11 of the 14 participants showed
impaired recall for phonologically similar words
for both the control and the phonological strategy
groups compared to the 8 out of 14 under
semantic coding instructions. Our results therefore suggest that both control and phonological
groups continue to encode phonologically at this
slower rate. Our final experiment is concerned
with the word length effect. If, as we speculated,
the inconclusive results of Experiment 2 reflect
the difficulty of processing longer words presented at a rapid rate, then we might expect to
Stimuli and procedure. These were the same as
in Experiment 2, except that the presentation rate
was one item every 2 seconds (950 ms on, 1050 ms
off).
Results and discussion
Means of the percentage of correct recall are
presented in Table 4. A 2 (word length)3
(induced strategy) mixed analysis of variance
showed a main effect of strategy, F(2, 42)5.29;
MSe327.12; p.01; hp 2 0.20, no overall effect
of word length, F(1, 42)1.76; MSe27.46; p
.19; hp 2 0.04, and a significant interaction between strategy and word length, F(2, 42)7.46;
MSe27.46; pB.01; hp 2 0.26. This interaction
was studied by tests of main effects. These tests
revealed that there was a main effect of word
length in the phonological condition, F(1, 42)
9.66; MSe54.92; pB.01; h2 0.19, whereas the
main effect of word length in the control group
was not significant, F(1, 42)2.02; MSe54.92;
p.16; h2 0.05. Unexpectedly, the main effect
of word length was significant in the semantic
condition, but in the direction of better performance on long words, F(1, 42)5.00; MSe
54.92; p.03; h2 0.11. In contrast to Experiment 2, therefore, results showed that strategy
induction had a marked impact on the effect of
TABLE 4
Experiment 4
Induced strategy
Short words
Long words
Difference
Semantic
Phonological
Control
74.22 (11.95)
78.50 (9.17)
4.28 (8.18)
73.50 (16.63)
67.55 (15.32)
5.95 (6.40)
86.95 (12.10)
84.22 (13.39)
2.72 (7.54)
Means (and standard deviations) of the percentages of
correct responses as a function of word length and induced
strategy in Experiment 4.
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CAMPOY AND BADDELEY
word length, an effect that was significant for
both short and long words; respectively, F(2,
42)4.55 and 6.48; MSe188.57 and 166.01;
pB.03; h2 0.18 and 0.24. Short words were
better recalled in the control group than in the
semantic or phonological groups, respectively,
F(1, 42)6.44 and 7.19; MSe188.57; p.01;
h2 0.13 and 0.15, whereas long words were
worse recalled in the phonological group than in
the semantic or control groups, respectively, F(1,
542)5.41 and 12.55; MSe166.01; pB.03; h2 0.11 and 0.23. As predicted, a majority of
phonologically instructed participants showed
better performance for short words (12 out of
15). The opposite effect was shown in the
semantic group with 12 of the 15 showing a long
word advantage, while in the control group 8 of
the 15 showed a short word advantage.
GENERAL DISCUSSION
Results throughout this study showed that strategy
instructions had marked consequences on the
phonological similarity and word-length effects.
With respect to the effect of phonological similarity, Experiment 1 showed better recall of dissimilar
words in both phonological and control groups,
while in accordance with our initial expectations
the induction of the semantic strategy resulted in
the elimination of the phonological similarity
effect. Results were equivalent in Experiment 3,
in which the presentation rate was slowed from
one item per second to one item every 2 seconds.
Results regarding the word-length effect were
more complex. In Experiment 2, strategy had only
a marginal effect, showing a tendency in the
predicted direction of a smaller word-length effect
in the group instructed to use a semantic strategy.
With a slower presentation rate in Experiment 4,
however, the effect in the semantic group was not
only eliminated but reversed, whereas the
standard word length effect was found in the
phonological group. Although this result was unexpected, reverse word-length effects have been
described previously in the literature by Romani
et al. (2005).2 In that study a reverse effect was
2
A reverse word-length effect has also been found by
Caplan and collaborators (Caplan & Waters, 1994; Caplan et
al., 1992), but this effect was probably a consequence of
problems with the word sets, such as differences in
phonological similarity (see Baddeley & Andrade, 1994;
Mueller et al., 2003).
found when words were presented under articulatory suppression, a procedure in which participants were instructed to articulate an irrelevant
word or phrase repeatedly in order to prevent
subvocalisation. According to Romani et al.
(2005) this reverse effect could be a consequence
of the fact that, under suppression, redintegration
processes become more relevant, given that participants tend to rely on lexical-semantic representations in this situation. They suggest that long
words would benefit more from redintegration
because, being longer, they could provide more
fragments of phonological information, reducing
the number of suitable candidates in long-term
memory (Brown & Hulme, 1995). However, this
account raises the question of why a number of
previous articulatory suppression experiments
resulted in the mere elimination of the length
effect rather than in its inversion (Baddeley,
Chincotta, Stafford, & Turk, 2002; Baddeley,
Lewis, & Vallar, 1984; Neath & Surprenant,
1995; Neath, Surprenant, & LeCompte, 1998).
An alternative, and perhaps more parsimonious,
explanation could be that the reverse effect in the
present experiment, and possibly that of Romani
et al. (2005), was a consequence of some uncontrolled characteristic of the stimuli. While long
and short words were matched on word frequency,
rated familiarity, imageability, and concreteness,
further examination of the two sets suggested the
possibility that our longer words might be easier to
relate to each other semantically.
We explored this possibility by asking a group
of 48 undergraduates from the University of
Murcia to rate, on a scale of 1 to 7, the level to
which the words from each set could be semantically related to each other. The mean rating for
long words was 4.15 (SD1.64) and for short
words, 2.98 (1.36), a statistically significant difference (M difference1.17; SD difference1.78);
t(47)4.54; pB.01. Although it was clearly undesirable that our long and short word sets differ
in this way, it does in fact strengthen the evidence
for the effectiveness of our two strategic instructions, leading to diametrically opposite word
length effects based on phonological versus semantic strategy instructions. The absence of a
clear effect in either direction in the control
group, in contrast to a clear standard word length
effect at the 1-second presentation rate, suggests
that slower presentation leads to a wider range of
strategies, with some participants still relying on
phonological coding, while others were presumably using an alternative, possibly semantic code.
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STRATEGIES AND IMMEDIATE SERIAL RECALL
Table 5 shows the effect size of the phonological similarity and word length effects across the
four experiments, expressed in terms of Cohen’s
d. The effect size for both phonological similarity
and word length was consistently greatest under
phonological instruction, and least under semantic coding. Under control conditions we observed
a substantial effect of phonological similarity at
both rates of presentation, and a rather weaker
word length effect at the 1-second rate, that was
further reduced at the slower 2-second rate,
probably because the reduced rate of presentation gave more scope for developing and using a
wider range of strategies. Under semantic coding
instructions, the effects of phonological similarity
were weaker at both rates of presentation, while
in the case of word length a modest decrement for
long words at the faster rate reverses when more
time is allowed. These results are consistent with
the assumption that phonological coding is relatively easy at rapid rates of presentation, but may
become less common when presentation rate
decreases, allowing other strategies to develop.
Our results have implications at both a methodological and theoretical level. Methodologically, they indicate that the same material may
be encoded semantically or phonologically, and
that the relevant encoding strategies can be
influenced by instruction. However, our results
also indicate that there are limits to such strategic
control, with verbal/phonological coding being
particularly appropriate with rapid presentation,
while effective semantic coding of unrelated
words appears to require slower rates. Placing
these results in the broader context of studies
described in the introduction, phonological coding appears to be particularly appropriate when
serial order is required under rapid presentation
conditions. Provided the material broadly conforms to the speaker’s language habits, rehearsal
is relatively easy and does not impose a demanding executive load. On the other hand, the
phonological code is relatively impoverished
compared to the richness of semantic encoding,
leading to a more limited capacity and poorer
long-term storage and retrieval (Craik & Lockhart, 1972). As such, it is optimal for short lists of
items, where serial order is critical and semantic
coding difficult.
In contrast, semantic coding is richer leading to
better long-term encoding. As a result, it is
advantageous in situations where the retention
of item information is crucial, for example when
large or open sets of words are used, rather than
the small closed sets that characterise studies
based on digits, letters, or limited word pools. It is,
however, less easy to encode serial order semantically when arbitrary sequences of items are
used, hence the need for more encoding time.
However, this is not the case when sequences are
able to take advantage of language habits, as in
sentence recall (Baddeley & Ecob, 1970; Baddeley, Hitch, & Allen, 2008). Semantic coding is
therefore likely to be helpful for sequences that
exceed the optimal length for phonological encoding, and for tasks where item information is
critical. Finally, one should note that, given
appropriate material, both semantic and phonological encoding can proceed in parallel, with
both enhancing performance (Baddeley & Ecob,
1970; Baddeley et al., 2008).
What of the theoretical implications of our
results? They do not, and were not intended to,
decide between theoretical options, but they do
have implications for the way in which one might
account for data of critical theoretical significance, namely a number of observations that
phonological coding effects appear to disappear
as list length increases (Hall et al., 1983; Hanley
& Broadbent, 1987; Jones, Hughes & Macken,
2006; Salamé & Baddeley, 1986). One interpretation of this phenomenon is in terms of the
abandonment of a phonological coding strategy
(Baddeley & Larsen, 2007). The potential capacity to control strategy by instruction offers the
possibility of testing this hypothesis directly,
TABLE 5
Effect size (Cohen’s d) of phonological similarity and word length effects in Experiments 14
Induced strategy
Experiment
1
2
3
4
Effect
Similarity
Word length
Similarity
Word length
Presentation rate
1
1
2
2
s
s
s
s
per
per
per
per
item
item
item
item
337
Semantic
Phonological
Control
0.33
0.43
0.28
0.52
1.79
1.22
1.13
0.93
1.06
0.65
0.97
0.36
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CAMPOY AND BADDELEY
against other hypotheses; for example that longer
list lengths simply overload the phonological
system, rendering phonological coding unhelpful
regardless of strategy. The results of such a study
would be particularly relevant to the multicomponent model of working memory (Baddeley,
2007), but would also inform other theoretical
approaches to STM such as the feature hypothesis
(Nairne, 1990) the SIMPLE model (Brown,
Neath, & Chater, 2007) and Cowan’s (2005)
embedded processes model, which do not necessarily assign a separate status to the process
involved in short-term phonological storage.
In conclusion, our results reinforce the results
of Hanley and Bakopoulou (2003) in suggesting
that strategies can be reliably manipulated by
instruction. Second, they provide preliminary
support for the argument that differences in
strategy may underpin some of the apparent
differences in empirical findings within the field.
They do not, of course, demonstrate that such
explanations are in fact correct, but they do
provide a way ahead, both through the direct
manipulation of strategy under the relevant conditions and, in the longer term, through the
development of indirect methods. For example,
if strategy instruction can be used in neuroimaging studies to identify a clear signature for
phonological and semantic strategies, then this
would allow the monitoring of strategies used by
participants in imaging studies, and as such should
benefit both subsequent theoretical interpretation, and the standardisation of methods across
laboratories.
Manuscript received 22 August 2007
Manuscript accepted 14 December 2007
First published online 30 March 2008
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APPENDIX A
Spanish nouns used in Experiments 1 and 3
Dissimilar word Phonetic transcription
BOTE
CIMA
FOCO
MURO
PERA
PINO
RUTA
SOPA
English translation
boat
summit
spotlight
wall
pear
pine
route
soup
Similar word
Phonetic transcription
LAGO
LAZO
MAGO
PALO
PATO
RAMO
SACO
VASO
English translation
lake
bow
magician
stick
duck
bouquet
sack
glass
APPENDIX B
Spanish nouns used in Experiments 2 and 4
Short word
CUBO
FOCO
GOMA
LAGO?
NIDO
PIPA
TAZA
VENA
Phonetic transcription
English translation
bucket
spotlight
rubber
lake
nest
pipe
cup
vein
Long word
GARAJE
JINETE
MALETA
NEVERA
REGAZO
SOTANA
TESORO
ZAPATO
Phonetic transcription
English translation
garage
rider
suitcase
fridge
lap
cassock
treasure
shoe