Sean FergusonPSY101 Lab Section #Spring 2013Blair, R. J. R.docx

Sean Ferguson
PSY101 Lab Section #
Spring 2013
Blair, R. J. R., Mitchell, D. G. V., Richell, R. A., Kelly, S.,
Leonard, A. & Newman, C. (2002). Turning a deaf ear to fear:
Impaired recognition of vocal affect in psychopathic
individuals. Journal of Abnormal Psychology, 111, 682-686.
doi: 10.1037/0021-843X.111.4.682.
Introduction
Psychopathy is a severe personality disorder marked by a
distinct pattern of antisocial behavior and emotional
characteristics. These include “callousness, a diminished
capacity for remorse, and superficial charm as well as
impulsivity and poor behavioral controls” (Blair, Mitchell,
Richell, Kelly, Leonard, & Newman, 2002, p. 682). Perhaps
most importantly, psychopaths seem to lack an intrinsic sense of
morality. As a result, many are capable of horrific crimes for
which they feel no guilt. Although psychopathic individuals
have been extensively studied, they are still not well
understood.
Recent studies have attempted to explain why psychopaths
exhibit such extreme emotional dysfunction. Currently, there
are two popular perspectives used to address this question. One
explanation, the low-fear model, suggests that much of a
psychopath’s aberrant behavior can be attributed to an impaired
ability to experience fear (Blair et al., 2002). Basically,
psychopaths never learn to avoid dangerous situations because
they fail to feel fear in dangerous situations. They tend to put
themselves in threatening positions (by starting a fight, for
example) because they do not fear the consequences for
themselves or others. In support of this explanation, previous
studies have suggested that psychopathic individuals lack
appropriate fear and startle reflexes in comparison with normal

individuals. The second explanation, the violence inhibition
mechanism (VIM) model, posits that the ability to read
expressions of fear or sadness on other people’s faces is what
allows people to develop morality. Normal people learn to
avoid behaviors that tend to cause other people to feel and
appear sad or afraid. The VIM model argues that psychopaths
have an impaired ability to identify sad and fearful expressions,
and so they do not learn to avoid immoral behaviors that cause
others to feel negative emotions (Blair et al., 2002).
Many previous studies have looked into psychopaths’
ability to identify facial expressions. However, none have
investigated the ability of psychopathic individuals to identify
the emotional intonation of spoken words. The purpose of this
study was “to explore the ability of psychopathic individuals to
recognize emotional vocal intonalities” (Blair et al., 2002, p.
683).
Methods
The study took place in a London prison. Potential
participants were screened using the Psychopathy Checklist -
Revised, a measure of psychopathic tendencies. Nineteen men
were identified as psychopaths. Twenty other men who did not
meet the criteria for psychopathy also took part in the study
(Blair et al., 2002).
Each participant took the Vocal Affect Recognition Test,
which consisted of 60 neutral stimulus words spoken in an
emotional vocal tone. Each tone reflected happiness, disgust,
anger, sadness, or fear. Participants were asked to listen to
each of the words and then identify the emotional tone of the
word. The independent variable in this study was psychopathy
(whether or not psychopathy was present in the individual), and
the dependent variable was performance on the Vocal Affect
Recognition Test (Blair et al., 2002).
Results/Discussion
The results showed that the psychopathic participants were
far less able to correctly identify fearful voices than the
nonpsychopathic participants. They were also less accurate

than the nonpsychopathic participants at identifying sad voices.
These findings correspond with previous findings that
psychopathic individuals have difficulty recognizing facial
expressions of fear and sadness. The findings also show that
psychopathic individuals’ inability to recognize these negative
emotions applies to auditory information in addition to visual
information (Blair et al., 2002).
The authors do not explicitly mention any weaknesses of their
study, but the small sample size is a drawback and should be
considered. In addition, the authors mentioned that these
results relate to previous findings of dysfunctional activity of
the amygdala in the brains of psychopathic individuals. They
suggest that further research involving brain imaging should be
done to discover more about the structural brain abnormalities
that may contribute to psychopathy (Blair et al., 2002).
How Quickly They Forget: The Relationship Between
Forgetting
and Working Memory Performance
Donna M. Bayliss
University of Western Australia
Christopher Jarrold
University of Western Australia and University of Bristol
This study examined the contribution of individual differences
in rate of forgetting to variation in
working memory performance in children. One hundred and
twelve children (mean age 9 years 4 months)
completed 2 tasks designed to measure forgetting, as well as
measures of working memory, processing
efficiency, and short-term storage ability. Individual differences
in forgetting rate accounted for unique

variance in working memory performance over and above
variance explained by measures of processing
efficiency and storage ability. In addition, the nature of the
variation in forgetting was more consistent
with a nonexecutive forgetting parameter than an executive
ability associated with resistance to inter-
ference. These findings indicate that individual differences in
the rate at which information is lost from
memory is an important constraint on children’s working
memory performance, which has implications
for current models of working memory that do not incorporate
such a factor.
Keywords: working memory, forgetting rate, executive ability
The construct of working memory is of considerable interest to
researchers because of the well-established relationship between
performance on tasks designed to assess the capacity of working
memory and cognitive skills such as reasoning ability (Kyllonen
&
Christal, 1990), language comprehension (Daneman & Merikle,
1996), reading and mathematics ability (Hitch, Towse, &
Hutton,
2001), and general fluid intelligence (Oberauer, Schulze,
Wilhelm,
& Süß, 2005). Recent research has explored this relationship
both
directly, by examining the factors that influence the predictive
relationship between working memory and cognition (Friedman
&
Miyake, 2004; Lépine, Barrouillet, & Camos, 2005; Unsworth &
Engle, 2005, 2007b), and also indirectly, by identifying the
factors
that constrain working memory performance and thus are likely
to
be important for higher level cognitive skills (Barrouillet,

Portrat,
& Camos, 2011; Bayliss, Jarrold, Gunn, & Baddeley, 2003;
Kane,
Bleckley, Conway, & Engle, 2001; Unsworth & Engle, 2007a).
This has led to the development of a number of theories about
the
nature of working memory and its relationship to higher order
cognition.
Many of these theories have postulated the involvement of a
central executive or attentional control system in working
memory
(Cowan, 1999; Engle, Kane, & Tuholski, 1999). For example,
Engle and colleagues (Engle, Kane, & Tuholski, 1999; Kane et
al.,
2001) argued that working memory consists of a short-term
stor-
age component and a controlled attention component, which
they
likened to the central executive in Baddeley and Hitch’s (1974)
original working memory model. The controlled attention
compo-
nent was thought to be a limited-capacity mechanism
responsible
for focused, goal-directed processing in the face of interference
or
distraction. Engle and colleagues (Engle, Kane, & Tuholski,
1999;
Kane, Bleckley, Conway, & Engle, 2001) argued that individual
differences in the capacity for controlled attention were
responsi-
ble for the strong relationship between working memory perfor-
mance and higher level cognition. In support of this, Engle,
Tuhol-
ski, Laughlin, and Conway (1999) showed that residual variance
from a working memory variable that remained once variance

common to short-term memory was removed was significantly
correlated with a fluid intelligence variable (see also Conway,
Cowan, Bunting, Therriault, & Minkoff, 2002; Towse &
Houston-
Price, 2001). They suggested that this residual variance in
working
memory performance reflected the controlled attention or
execu-
tive component of working memory (though see Colom,
Rebollo,
Abad, & Shih, 2006). Bayliss, Jarrold, Gunn, and Baddeley
(2003)
have also shown that residual variance in working memory span
performance that remains once variance associated with the pro-
cessing and storage operations involved in the working memory
span task is removed reliably predicts reading and mathematics
performance in both children and adults (see also Towse &
Houston-Price, 2001). These findings indicate that this residual
variance does not simply reflect measurement error (see also
Jarrold & Bayliss, 2007) but instead indexes an additional
factor
that is important for higher level cognitive performance. In line
with the suggestion of Engle and colleagues, Bayliss et al.
attrib-
This article was published Online First August 4, 2014.
Donna M. Bayliss, Neurocognitive Development Unit, School of
Psy-
chology, University of Western Australia; Christopher Jarrold,
Neurocog-
nitive Development Unit, School of Psychology, University of
Western
Australia, and School of Experimental Psychology, University
of Bristol.

This research was supported by Economic and Social Research
Council
(ESRC) Grant RES-000-22-0606 and Australian Research
Council (ARC)
Discovery Project DP0988288. We would like to thank all the
schools and
children who made this research possible and Klaus Oberauer,
Nelson
Cowan, and Emily Elliot for comments and suggestions on an
earlier
version of the manuscript.
Correspondence concerning this article should be addressed to
Donna M.
Bayliss, School of Psychology, Mailbag M304, The University
of Western
Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
E-mail:
[email protected]
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Journal of Experimental Psychology:
Learning, Memory, and Cognition
© 2014 American Psychological Association
2015, Vol. 41, No. 1, 163–177

0278-7393/15/$12.00 http://dx.doi.org/10.1037/a0037429
163
mailto:[email protected]
http://dx.doi.org/10.1037/a0037429
uted this residual variance to an executive ability that is
involved
in working memory span performance (see also Bunting, 2006;
Conway et al., 2002; Towse & Houston-Price, 2001; Unsworth
&
Spillers, 2010).
However, the interpretation of this residual variance as
executive
has been purely speculative, and to date, there have been few
direct
attempts to specify exactly what it is that this residual variance
captures. One possibility is that it does indeed reflect domain-
general executive attention as Engle and his colleagues
suggested.
In support of this, Kane et al. (2004) derived a single domain-
general executive-attention factor and two domain-specific
storage
factors from a battery of verbal and visuospatial working
memory
and short-term memory tasks and showed that the executive-
attention factor was closely associated with a fluid intelligence
variable. The executive-attention variable elicited high loadings
from the verbal and visuospatial working memory tasks and
lower
loadings from the short-term memory tasks, providing support
for
the claim that it represented a domain-general factor associated

with higher level cognition. Kane et al. argued that the variance
captured by this factor reflected the ability to maintain
information
in an active state, particularly in the presence of interference
and/or
competition between response alternatives that must be
resolved.
The finding that individuals with low working memory capacity
suffer from proactive interference to a greater extent than
individ-
uals with high working memory capacity when asked to recall a
series of lists with overlapping memory items is consistent with
this executive-attention account (Kane & Engle, 2000). More
recent versions of this account have argued that the extent to
which
executive attention is required to maintain and/or recover access
to
memoranda is determined by the amount of conflict, distraction,
or
interference present in the task context (Kane, Conway,
Hambrick,
& Engle, 2007). Thus, the residual variance captured by
working
memory tasks could be thought of as reflecting the executive-
attention resources required to prevent the deleterious effects of
interference on working memory performance.
A potentially related suggestion is that the residual variance in
working memory performance is associated with individual
differ-
ences in the degree to which information is lost during the
working
memory task due to forgetting. Forgetting from short-
term/work-
ing memory has typically been attributed to one of two main
causes, namely, a passive process of decay over time

(Barrouillet,
Bernardin, & Camos, 2004; Barrouillet, Bernardin, Portrat, Ver-
gauwe, & Camos, 2007; Barrouillet, De Paepe, & Langerock,
2012; Ricker & Cowan, 2010) or some form of interference that
could be either retroactive, as in interference from subsequent
events within the task (Lewandowsky, Duncan, & Brown, 2004;
Lewandowsky, Geiger, Morrell, & Oberauer, 2010), or
proactive,
as in interference that builds up between memoranda across suc-
cessive trials (Bunting, 2006; Keppel & Underwood, 1962). Re-
gardless of which of these factors is responsible for forgetting
from
working memory, there is some evidence to suggest that
individ-
uals may indeed vary in the rate or degree to which they forget
information. For example, Cowan and colleagues (Cowan,
Nugent,
Elliott, & Saults, 2000; Saults & Cowan, 1996) have shown
age-related differences in the rate of forgetting of auditory
mem-
ory. Using an ignored speech paradigm, Cowan et al. (2000)
found
that younger children showed more rapid forgetting of
unattended
information across a filled retention interval than older
children.
Crucially, however, this difference was limited to the last item
in
the unattended list, with no such age differences found for
earlier
serial positions or for the attended speech condition. Cowan et
al.
argued that the final serial position was free from retroactive
interference from other list items, and so, age differences in
degree

of forgetting localized to this serial position were best
accounted
for in terms of a developmental increase in the retention of
audi-
tory sensory memory. Moreover, this aspect of memory
develop-
ment was argued to be independent of attention. In adults, Un-
sworth, Brewer, and Spillers (2011) have also shown that
individual differences in working memory capacity are
associated
with differences in forgetting. In their study, high working
mem-
ory capacity participants showed better memory for paired asso-
ciates than low working memory participants across a range of
retention intervals but performed comparably when tested
imme-
diately after presentation of a given pair. Unsworth et al. argued
that variation in working memory capacity could be explained
in
terms of differences in controlled retrieval processes that act to
limit the size of the search set at retrieval and ultimately
influence
the amount of information that individuals forget across a
retention
interval. Thus, there is some evidence that individuals may vary
in
the rate at which they lose information from memory.
One might ask whether this variation in forgetting rate is simply
a reflection of variation in the opportunity to engage in
refreshing
or reactivation of memory traces that in turn follows from
differ-
ences in the speed with which individuals complete processing
operations. Barrouillet and colleagues (2004, 2007; Barrouillet,
Gavens, Vergauwe, Gaillard, & Camos, 2009; see also Bayliss,

Jarrold, Baddeley, Gunn, & Leigh, 2005; Jarrold & Bayliss,
2007)
argued that engaging in the processing activity of the working
memory span task prevents individuals from carrying out active
maintenance of the to-be-remembered items (cf. Barrouillet &
Camos, 2001; Towse, Hitch, & Hutton, 2002). As a consequence
of this, the speed with which individuals complete the
processing
operations leads to variation in the time during which forgetting
can occur while maintenance activities are prevented. Evidence
to
support this suggestion comes from a recent study by
Barrouillet et
al. (2012), who showed that lengthening the duration of the pro-
cessing activity while maintaining a constant time between the
end
of each processing activity and presentation of the subsequent
storage item (i.e., the time available for restoring or refreshing
the
memory trace) resulted in poorer memory performance,
consistent
with the idea that longer processing leads to greater forgetting
(see
also Bayliss et al., 2005, who showed that age-related changes
in
a speed of processing variable accounted for unique variance in
working memory span performance). In addition, by systemati-
cally manipulating the amount of time during which children
were
engaged in processing and the time they had available for
refresh-
ing memory items, Barrouillet et al. (2009) were able to show
that
the slope relating the time available for refreshing memory
items
with working memory span performance was steeper in older

relative to younger children. They argued that this provided evi-
dence of a faster rate of reactivation in older children (see also
Bayliss et al., 2005; Gaillard, Barrouillet, Jarrold, & Camos,
2011;
Tam, Jarrold, Baddeley, & Sabatos-DeVito, 2010).
However, variation in the time available for forgetting and the
time available for refreshing cannot explain the residual
variance
found by Bayliss et al. (2003), as the variation in working
memory
span associated with individual differences in processing speed
and storage ability was statistically removed in this earlier
work.
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164 BAYLISS AND JARROLD
Similarly, Ricker and Cowan (2010) argued that models that
propose an equilibrium between forgetting and reactivation pro-
cesses cannot explain the pattern of forgetting observed in their
study. They presented adult participants with either three
uncon-
ventional visual characters or six English letters in a memory

array, followed by a retention interval of either 1,500, 3,000, or
6,000 ms. The retention interval was either unfilled (i.e., a no-
load
condition) or filled with a distractor activity that varied in diffi-
culty (i.e., in Experiment 1, repeating digits vs. performing sub-
traction). For the English letter condition, no forgetting across
retention intervals was evident for the no-load condition, in
which
participants were free to use maintenance strategies, whereas
sig-
nificant forgetting was observed across retention intervals when
maintenance strategies were blocked by the inclusion of a
distrac-
tor activity. Crucially, in the unconventional character
condition,
while introducing a distractor activity significantly impaired
per-
formance in the load conditions relative to the no-load
condition,
the rate of forgetting that was observed across the measured
retention intervals was equivalent for all conditions. Ricker and
Cowan suggested that for certain stimuli—in this case, the
uncon-
ventional visual stimuli—some features of the stimulus are
inev-
itably lost over time and cannot be refreshed via attentional or
rehearsal mechanisms. This finding is significant as it demon-
strates a time-based loss of information that is independent of
any
cognitive load. In relation to the Bayliss et al. study, this leads
to
the possibility that individuals may vary in the extent to which
they
forget information while engaged in the processing activity of a
working memory task and that this is what the residual variance
in

working memory span performance represents. To our
knowledge,
the extent to which individual differences in the rate with which
individuals forget information contribute to working memory
per-
formance, independently of storage and processing ability, has
never been studied before.
The first aim of this study was, therefore, to examine whether
residual variance in working memory span performance, which
remains once variance associated with the processing and
storage
operations has been removed, is related to individual
differences in
rate of forgetting. Evidence to support this claim would have
important implications for current theories of working memory,
most of which do not incorporate a forgetting rate factor
indepen-
dent of other storage and processing abilities. If an independent
contribution of forgetting rate to working memory span perfor-
mance can be established, the next logical question is what
under-
lies this variation in forgetting rate. The literature offers a
number
of possible answers to this question that could be broadly
classified
into either controlled, strategic, executive-type factors on the
one
hand or more basic, automatic, nonexecutive factors on the
other.
For example, Engle and colleagues would suggest that variation
in
rate of forgetting is mediated by an executive ability associated
with resisting interference either from subsequent events that
occur
within the trial (i.e., distractor activity) or from similar memory

items presented in previous trials (i.e., proactive interference;
see
also, Unsworth et al., 2011). However, other possible causes of
variation in forgetting rate include individual differences in
more
basic parameters such as decay or interference effects that are
not
executive in nature. It has certainly been suggested that
individuals
may vary in the rate at which information decays from memory
during processing (Barrouillet et al., 2009; Cowan, Saults, &
Nugent, 1997; Hitch, Towse, & Hutton, 2001; Oberauer &
Kliegl,
2001; Portrat, Camos, & Barrouillet, 2009), and the rate of such
trace decay could vary between individuals independently of
any
attentional control processes that might serve to offset it.
Similarly,
it is plausible that individuals may differ in their susceptibility
to
interference effects, such as feature overwriting (e.g., Nairne,
1990), that occur simply by virtue of representations sharing
overlapping features. The second aim of this research was,
there-
fore, to systematically manipulate the factors expected to
contrib-
ute to the rate of forgetting to examine which, if any, of these
possibilities best accounted for the residual variation in working
memory span performance.
To address these goals, two interpolated tasks were designed to
measure rate of forgetting in children. Children were the chosen
sample for this study for two reasons. First, there is
considerable
variation in working memory and executive abilities in a sample

of
children, partly because these processes are still undergoing de-
velopment. As a result, the range of abilities evident in a
sample of
children is usually larger than in a typical sample of
undergraduate
students, which makes a child sample ideal for individual-
differences studies. Second, in our previous work, we
successfully
developed a method for fractionating the sources of variance
contributing to working memory performance in children
(Bayliss
et al., 2003, 2005), and we employed the same approach here.
This
study extends that work by including additional measures of
for-
getting. In these forgetting rate tasks, participants were
presented
with three to-be-remembered words and were then required to
complete a continuous processing activity for either a short or
long
duration before recalling the to-be-remembered items. These
tasks
were designed to measure the amount of information that people
forget when maintenance activities are prevented by a
continuous
processing activity. It was expected that recall performance
would
be poorer in the long-duration conditions relative to the short-
duration conditions as maintenance activities would be
prevented
for longer, thus allowing more forgetting to occur (cf. Brown,
1958; Peterson & Peterson, 1959; Towse et al., 2002). If
residual
variation in working memory span performance reflects
individual

differences in forgetting, then we would expect to see a
relation-
ship between the residual variance derived from working
memory
span tasks and performance on the two forgetting tasks.
To address the second aim of this study and to characterize the
nature of any variation in forgetting rates that might be related
to
residual variance in working memory, the amount of
interference
encountered in the two forgetting tasks was manipulated by (a)
systematically varying the interpolated processing activity in-
volved in each task and (b) deriving measures of proactive
inter-
ference effects by contrasting performance on the first half
versus
the second half of trials. The relationship between each of these
measures and residual variation in working memory span was
then
examined. If the residual variation in working memory span re-
flects variation in an executive factor associated with resistance
to
interference, then we would expect to see a stronger association
between the residual variance and performance on the forgetting
task that involved a greater degree of interference, whether that
was from increased interference from the interpolated distractor
activity or from increased interference from previous trials (i.e.,
proactive interference). In contrast, if the residual variance best
reflects a basic forgetting rate parameter, then the association
between the residual variance and the measures of forgetting
should be comparable.
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165FORGETTING AND WORKING MEMORY SPAN IN
CHILDREN
Method
Participants
A total of 117 children participated in the study with full
parental consent. Of these children, the data from four children
were excluded because they did not complete all the tasks in the
battery due to absence on the final days of testing or to moving
out
of the area. The data from one additional child were excluded
because the school identified the child as having difficulties
asso-
ciated with an autistic spectrum disorder. The mean age of the
remaining 112 participants was 9 years 4 months (range 8;9 –
10;2).
Design
Each child completed the battery of tasks in four separate
sessions on different days. In the first session, each child com-
pleted the object speed task followed by the object working
mem-
ory span task. The order of presentation of the forgetting tasks

was
counterbalanced across participants in the second and third ses-
sions. Half of the children completed the color forgetting task
and
the digit span task in the second session and the object
forgetting
task and the counting speed task in the third session. For the
remaining participants, the order of presentation of these
sessions
was reversed. In the fourth session, all children completed the
counting working memory span task followed by the word-span
task.
Tasks and Procedure
All tasks were presented on a 15-in. Elo USB Touchscreen
controlled by a laptop computer.
Forgetting tasks. Each participant completed two forgetting
tasks: the color forgetting task and the object forgetting task. In
both tasks, a trial commenced with the sequential presentation
of
three to-be-remembered words in black 48-point Helvetica font
on
a white background. Each word was presented for 1 s, followed
by
a 300-ms interstimulus interval during which the screen was
blank.
To counteract any difficulties with word reading, each word was
simultaneously presented auditorily in a female voice.
Following
the presentation of the last word, the display screen changed to
signal the beginning of the continuous processing activity. The
display screen used for the processing activity consisted of nine
different colored squares (red, blue, green, yellow, pink,
orange,

purple, white, and brown) measuring 35 mm each side,
presented
in a random arrangement on a grey background.
In the color forgetting task, the processing activity involved the
auditory presentation of color names in a male voice. The
children
were required to locate the appropriately colored square and
touch
it as quickly as they could. In the object forgetting task, the
processing activity involved the auditory presentation of object
names that reliably cued one of the nine colors (i.e., banana �
yellow). The children were asked to think of the color typically
associated with the object and then touch the appropriately
colored
square on the screen as quickly as possible. As soon as the child
responded by touching the screen, the next processing item was
presented. To prevent articulatory rehearsal, the children were
also
required to name the color of each square as they touched it.
Once
the processing activity had been performed for a specified dura-
tion, the children were presented with a blank screen,
simultane-
ously heard a brief tone to signal the end of the trial, and were
then
asked to recall the three to-be-remembered words in correct
serial
order.
Each forgetting task consisted of 16 trials, half of which were
presented with a short-duration processing activity of 4,000 ms
(short) and half of which were presented with a long-duration
processing activity of 8,000 ms (long). However, as the
continuous

processing activity did not end until the child made a response
to
the final processing item, these processing durations varied
slightly
(mean duration � 4,020.39 ms and 7,950.64 ms in the short and
long conditions, respectively). The trials were counterbalanced
so
that there were two short-duration and two long-duration
process-
ing activities presented within each consecutive set of four
trials.
The order of presentation of the trials was the same for each
participant. An additional four trials were presented at the start
of
each task as practice.
A pool of 60 single-syllable concrete nouns were selected from
the MRC Psycholinguistic Database on the basis that they were
high frequency (Kucera-Francis written frequency [K-F Freq] �
20) and had low age of acquisition (AOA � 500), high concrete-
ness (Conc � 400), and high imageability (Imag � 400) ratings
(see the Appendix). In addition, all words had a frequency
rating
from the Celex database of greater than 20. These words were
used
to form two pools of 30 words that were closely matched on the
variables above, Celex, t(58) � .52, K-F Freq, t(58) � .19,
AOA,
t(58) � �.01, Conc, t(58) � �.02, Imag, t(58) � .37, p � .10 in
all cases. One of these pools of words was assigned to the short-
duration condition, and the other was assigned to the long-
duration
condition. The same words were used in both the color and the
object forgetting tasks, but the order of presentation of these
words
varied.

To manipulate the amount of interference encountered in the
two forgetting tasks, the items used for the processing activity
of
each task varied (cf. Conlin, Gathercole, & Adams, 2005). The
items used in the processing activity of the color forgetting task
were the nine color names already described above, which were
expected to be relatively distinct from the storage items. In con-
trast, the processing items used in the object forgetting task
con-
sisted of 69 object names, which were expected to interfere with
the retention of the storage items to a greater extent as both sets
of
items were concrete nouns. The object names were selected
from
those used in Bayliss et al. (2005) on the basis that they reliably
cued one of the nine colors presented in the display screen (i.e.,
snow � white). In the color forgetting task, a nonexhaustive list
of
color names was created by randomizing consecutive lists of the
nine color names. Similarly, for the object forgetting task, a
nonexhaustive list of object names was created by randomizing
consecutive lists of the 69 object names. The same list of color
names and list of object names were then presented to all partic-
ipants. However, as the presentation of the processing items was
determined by the speed of each child’s responses, some
children
were able to complete more of these processing items within
each
processing activity than others. The timing and accuracy of re-
sponses to each processing item were recorded by the computer,
and participants’ recall responses were recorded by the experi-
menter. Items were scored correct if they were recalled in the
correct serial position, and the overall proportion correct was
calculated for each duration condition within each task.

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Working memory span tasks. Two working memory span
tasks were completed by each participant: the object working
memory span task and the counting working memory span task.
Both tasks involved a series of processing and storage episodes.
In
the object working memory span task, participants were
presented
with a display screen similar to that used in the processing
activity
of the forgetting tasks. Nine different colored squares
measuring
35 mm each side were presented on a grey background, with the
numbers 1 to 9 presented in the center of the squares in black.
At
the start of each processing episode, participants were presented
with a verbal object name that reliably cued one of the nine
colors
and were required to think of the color typically associated with
that object and then touch the appropriately colored square on
the
screen as quickly as possible. As they touched the square,

partic-
ipants were required to verbalize the number that was in the
center
of the square and remember that number for recall at the end of
the
trial. Following a set number of processing and storage
episodes,
participants were asked to verbally recall the numbers that they
had named during the trial in correct serial order. Trials
increased
from two to a maximum of six processing and storage episodes,
with four trials at each span length. Testing continued until a
child
failed all four trials at a given span length. An additional three
trials at Span Length 2 were given at the start of the task as
practice.
The 86 processing items used in the object working memory
span task were taken from Bayliss et al. (2003). All items were
recorded in a male voice and adjusted to 1 s in length by adding
silence to the start of the shorter items. To control for
differences
in processing difficulty across span lengths, trials were
organized
so that the mean reaction time to items within each span length
was
equated across span lengths, F(4, 220) � .57, p � .10, based on
response times to each item taken from previous work (Bayliss
et
al., 2003). In addition, each colored square in the display was
cued
approximately equally often in each serial position, and each of
the
digits 1–9 was cued approximately equally often in each serial
position.

The counting span task was adapted from one used by Towse,
Hitch, and Hutton (1998). The display screen consisted of an
array
of blue squares and red triangles presented in a random arrange-
ment in a white rectangle measuring 144 mm � 108 mm that
was
centered on the screen. To the left and right of this rectangle,
two
smaller rectangles measuring 47 mm � 65 mm were displayed
with the words Odd and Even presented in the center of the left
and
right rectangles, respectively. At the onset of each processing
and
storage episode, participants were presented with one of these
screens and were required to count the number of blue squares,
pointing to each square as they counted it, and to decide
whether
the total number of squares was an odd or even number. They
then
responded by touching the odd or even rectangle on the screen,
at
which point the squares and triangles disappeared and a digit
between 1 and 9 was presented in the center of the screen in
black.
Participants were asked to name the digit and remember it for
later
recall. After a series of processing and storage episodes, the
children were asked to recall the digits that they had named in
correct serial order. As with the object working memory span
task,
trials increased from two to a maximum of six processing and
storage episodes in length, with four trials at each span length
and
three additional trials presented at the start of the task as
practice.

Testing was terminated when a child failed all four trials at a
given
span length.
Eighty-six different counting arrays were created with 20 arrays
each consisting of 2, 3, 4, or 5 blue squares presented among
eight
red triangles, plus an additional six arrays that were created for
practice. An equal number of each of these array sizes were
presented at each span length, and the number of times an odd
counting array was followed by an odd or even digit and vice
versa
was approximately equal. In addition, each digit was presented
approximately equally often in each serial position.
The timing of the processing and storage episodes in both tasks
was carefully controlled. Participants were given 4,000 ms to
respond to the processing episode of each task (i.e., to find the
appropriately colored square or to count the blue squares and
make
an odd or even judgment). If a participant responded within this
time, the storage item was presented and remained on the screen
until a total of 5,000 ms had elapsed, at which point the next
processing episode was presented. If a child failed to respond
within 4,000 ms, the storage item was automatically presented
for
a further 1,000 ms before the presentation of the next
processing
episode. The accuracy and timing of participants’ responses to
the
processing items were recorded by the computer, and
participants’
recall responses were recorded by the experimenter at the time
of
testing. Trials were scored correct if items were recalled in the
correct serial position, and span scores were calculated by aver-

aging the last four correctly recalled trials (i.e., two trials
correctly
recalled at 2, one at 3, and one at 4 would give a span score of
2.75).
Storage tasks. Each participant completed two storage tasks:
a digit span task (which corresponded to the storage
requirements
of the working memory span tasks) and a word-span task. In the
digit span task, participants were visually presented with digits
between 1 and 9 in the center of the screen in black. The digits
were presented for 1,000 ms, followed briefly by a blank screen
before the presentation of the next digit. Participants were
asked to
name each digit as it was presented and then recall the digits in
correct serial order at the end of the trial. Trials increased from
three to a maximum of eight digits in length, with four trials at
each length. An additional two trials were given at the start of
the
task as practice. Each digit was cued approximately equally
often
in each serial position. Testing continued until a child failed all
four trials at a given span length. Span scores were calculated
as an
average of the last four correctly recalled trials.
In the word-span task, participants were visually presented with
words in black 48-point Helvetica font on a white background.
Each word was presented for 1,000 ms, followed by a blank
screen
for 300 ms and then the next word. As with the forgetting tasks,
each word was simultaneously presented auditorily in a female
voice. Trials increased from two to six words in length, with
four
trials at each span length and an additional two trials given at
the

start of the task as practice. The 84 words used in the word-span
task consisted of the 60 words used in the forgetting tasks plus
an
additional 24 words that also met the criteria described above.
Trials were organized so that any semantic associations between
the words within each trial were avoided as much as possible.
Testing continued until a child failed all four trials at a given
span
length, and span scores were calculated in the same way as in
the
digit span task.
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CHILDREN
Processing-efficiency tasks. Independent measures of pro-
cessing efficiency were taken using an object association task
and
a counting speed task. In the object association task,
participants
were presented with a display screen similar to that used in the
working memory span task but without any digits on the screen.
To

provide a measure of each child’s color knowledge and also as a
check for color blindness, participants were first presented with
each of the nine color names auditorily and were required to
touch
the appropriately colored square as quickly as possible. Once a
response was made, the screen was cleared, and a start button
was
presented. Children were asked to touch the start button when
they
were ready to proceed to the next trial. Following this, 36 of the
object names used in the working memory span task (four of
each
color) were presented auditorily, and participants were asked to
think of the color typically associated with each object and then
touch the appropriately colored square as quickly as possible.
This
corresponded to the processing activity of the working memory
span task, but without any storage requirements. Participants
were
then presented with each of the color names again and were
asked
to touch the correct square as quickly as possible.
In the counting speed task, participants were presented with 36
of the counting arrays (nine of each array size) used in the
counting
working memory span task and were asked to count the number
of
blue squares, ignoring the red triangles, and decide if the
number
was odd or even. They were then required to indicate their re-
sponse by touching either the Odd or Even button as quickly as
possible. If they responded correctly, they heard a boing noise,
the
screen was cleared, and a start button was presented to enable
them

to continue to the next trial. If they responded incorrectly, they
heard a low pitch tone, and the count array remained on the
screen
until they had responded correctly. Accuracy and response times
were recorded by the computer. Instructions and practice
examples
were given prior to the task using a card displaying a count
array.
Results
Preliminary Analysis
Response times in the processing-efficiency tasks were trimmed
to remove any extraneous responses. Initially, any response
times
greater than 10 s were removed. The remaining response times
were then Windsorized, in line with the recommendations of
Ratcliff (1993), by replacing any response times more than 2.5
standard deviations above the mean for each individual item
with
the cutoff value for that item. Participants’ response times to
the 36
object names in the object association task were then averaged
to
provide a measure of each individual’s object processing effi-
ciency. In the counting speed task, response times were
averaged
across the 36 counting arrays.
To ensure that the fixed list length of three items presented in
the forgetting rate tasks was within the capacity of each partici-
pant, an estimate of immediate recall performance was
calculated
from the four trials presented at List Length 3 as part of the
word-span task (i.e., a baseline measure of immediate recall

per-
formance at 0 ms). Only those participants who showed perfect
recall on these trials were included in the subsequent analyses
(n �
88).1 This has the added advantage of making sure that
estimates
of forgetting were derived relative to the same baseline level of
immediate recall across participants (see below). Of course,
indi-
viduals who are performing at ceiling on the baseline measure
may
have immediate recall capacities that extend beyond three items,
and so, even at this level of performance, there may be
differences
in the strength of encoding of the memory items across
individuals.
However, we would assume these to be collinear with individual
differences in storage capacity, which has been controlled for in
the subsequent analyses. Descriptive statistics for all measures
are
presented in Table 1.
Forgetting Tasks
Recall scores on the two forgetting tasks were subjected to a 2
�
2 repeated measures analysis of variance, with task (color,
object)
and duration (short, long) as the factors. This revealed a
significant
effect of task, F(1, 87) � 60.03, p � .001, �p2 � .41, reflecting
poorer performance on the object task relative to the color task.
There was also a significant effect of duration, F(1, 87) �
215.12,
p � .001, �p2 � .71, indicating that recall performance was

better
in the short conditions than the long conditions, and no
significant
interaction between task and duration, F(1, 87) � 0.05, p � .82,
�p
2 � .00. Thus, recall performance in the color and object condi-
tions was not differentially affected by the increase in retention
duration from 4,000 ms to 8,000 ms.
As the duration of the processing activity involved in the color
and object forgetting tasks varied slightly depending on the
point
at which participants made their final response within the pre-
scribed time window, it is possible that the task effect may have
been inflated by differences in the actual retention interval in
each
task. To examine this, a second analysis was conducted in which
slope and intercept values were derived for each participant,
based
on their average processing durations in the short and long
condi-
tions of both tasks, respectively. Processing durations were
taken
as the time between the onset of the processing activity and the
child’s response on the final processing item immediately prior
to
recall. The intercept values for the color and object forgetting
tasks
were then subjected to a paired-sample t test, which was signifi-
cant, t(87) � 2.43, p � .02, indicating that even when any
differences in processing duration were taken into account,
recall
performance in the object forgetting task was still worse than in
the

1 Analyses performed with the sample as a whole produced the
same
pattern of results. Specifically, the analysis of performance on
the forget-
ting rate tasks showed significant effects of task, F(1, 111) �
59.24, p �
.001, and duration, F(1, 111) � 253.04, p � .001, and no
interaction
between task and duration, F(1, 111) � 1.66, p � .20. Analysis
of the first
half of trials compared to the last half also revealed significant
effects of
trials, F(1, 111) � 15.30, p � .01, and task, F(1, 111) � 74.60,
p � .01,
and no interaction between task and trials (F � 1). An
exploratory factor
analysis showed a similar four-factor structure and, importantly,
a struc-
tural equation modeling analysis showed that the model
presented in Figure
1 also provided a good fit to the data from the larger sample,
�2(14) �
12.52, p � .57, with the storage ability, processing speed, and
forgetting
rate variables all significantly predicting the working memory
variable (all
ps � .05). Finally, the 0 – 4,000-ms object forgetting measure
did not
contribute any additional variance to the object or counting
working
memory span tasks (all ps � .10) over and above the significant
contri-
bution of the color forgetting measure but did contribute
significant vari-
ance when entered on the first step of the analyses, F(1, 108) �
5.65 and

10.29, p � .05, respectively. The only difference identified was
that the
unique contribution of the low proactive interference measures
to the
counting working memory span task was significant. Data are
available
from the first author on request.
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color forgetting task. In addition, analysis of the slope values
derived for each task revealed a nonsignificant difference,
t(87) � �0.28, p � .78, confirming the previous finding that
there
was no difference between the two tasks in the rate of forgetting
between 4,000 ms and 8,000 ms.
To provide a measure of the degree or rate of forgetting
across each task, two proportional difference scores were ob-
tained for each task by calculating the proportion decrease in
recall performance from a baseline measure (calculated as the
proportion correct on the four trials presented at List Length 3
as part of the word-span task) to performance at 4,000 ms

(0 – 4,000) and the proportion decrease in recall performance
from performance at 4,000 ms to performance at 8,000 ms
(4,000 – 8,000).2 Analysis of the estimates of forgetting (i.e.,
the
proportional difference scores) revealed a significant difference
between the 0 – 4,000-ms estimates from the color and object
tasks (Ms � .38 and .50, respectively), t(87) � �5.83, p �
.001, and between the 4,000 – 8,000-ms estimates from the
color
and object tasks (Ms � .35 and .45, respectively), t(86) � 2.35,
p � .02.
To provide an estimate of the amount of forgetting experi-
enced due to the buildup of proactive interference, two addi-
tional scores were obtained for each forgetting task by calcu-
lating the proportion correct on the first half of trials and
proportion correct on the second half of trials. Any evidence of
greater forgetting in the second as opposed to the first half of
trials would be consistent with the suggestion that proactive
interference builds up over trials and is maximal at the end of
the task. Consistent with this idea, a 2 � 2 repeated measures
analysis of variance, with task (color, object) and trials (first
half, second half) as the factors, revealed a significant effect of
trials, F(1, 87) � 12.14, p � .01, �p2 � .12, with poorer
performance in the second half of trials (M � 0.42, SD � 0.17)
relative to the first half of trials (M � 0.47, SD � 0.17). There
was also a significant effect of task, F(1, 87) � 82.80, p � .01,
�p
2 � .49, but no significant interaction between task and trials,
F(1, 87) � 0.51, p � .48, �p2 � .01.
Is Performance on the Forgetting Tasks Related to
Residual Variance in Working Memory
Span Performance?

To examine this initial question, we first explored the pattern of
correlations between the estimates of forgetting for each task,
the
working memory span measures, the storage measures, and the
measures of processing speed (see Table 2). The correlations
presented in Table 2 show that the two 0 – 4,000-ms forgetting
measures were closely related to each other, indicating that
there
was some shared variance between these two variables. These
two
forgetting measures were also associated with the working
mem-
ory span measures, suggesting that there may be a relationship
between these indices of performance. The two 4,000 – 8,000-
ms
forgetting measures were significantly correlated with each
other
but showed no reliable associations with the two 0 – 4,000-ms
forgetting measures or the two working memory span measures.
Finally, the working memory span measures showed significant
correlations with the independent measures of storage ability
and
the independent measures of processing efficiency.
These relationships were further examined by an exploratory
factor analysis performed using a maximum-likelihood
extraction
on the data from the four forgetting measures, the two working
memory span tasks, the two storage tasks, and the two measures
of
processing efficiency. This revealed a four-factor structure that
accounted for 71.01% of the total variance. The four-factor
solu-
tion was rotated using a direct oblimin procedure to facilitate
the
interpretation of the factors. The loadings from the pattern

matrix
are presented in Table 3. The two 0 – 4,000-ms forgetting
measures
loaded on the first factor, suggesting that this factor
corresponded
to a forgetting rate factor associated with the first 4,000-ms
period
of the forgetting tasks. The second factor appeared to represent
a
forgetting rate factor associated with the 4,000 – 8,000-ms
period,
2 A 4,000 – 8,000-ms forgetting rate estimate could not be
calculated for
one child as this child failed to recall any items correctly in the
short
condition of the object forgetting rate task. Thus, all analyses
involving this
variable are based on 87 participants.
Table 1
Summary of Descriptive Statistics for All Measures
Measure M SD Minimum Maximum Reliability Skew Kurtosis
Forgetting rate tasks
Color short .62 .20 .25 1.00 .64 �0.11 �1.06
Color long .39 .19 .00 .92 .68 0.54 0.21
Object short .50 .20 .00 .96 .68 �0.22 �0.06
Object long .27 .18 .00 .79 .64 0.49 �0.40
Working memory span
Object 4.32 0.77 2.25 5.75 .74 �0.43 �0.29
Counting 4.23 0.92 2.00 6.00 .76 �0.32 �0.44
Storage tasks

Digit span 4.66 0.62 3.25 7.00 .72 0.97 2.08
Word span 4.08 0.53 3.25 5.50 .69 0.52 �0.14
Processing efficiency
Object 2,680.34 425.24 1,636.57 3,476.79 .83 �0.12 �0.64
Counting 2,130.47 511.12 1,179.63 3,558.51 .92 0.77 0.50
Note. Values are proportion correct for forgetting rate tasks,
span scores for working memory and storage
tasks, and response times in ms for processing-efficiency tasks.
n � 88.
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CHILDREN
with loadings from the two 4,000 – 8,000-ms forgetting
measures,
and the third factor corresponded to a storage-related factor
with
loadings from the two working memory span measures and the
two
measures of storage ability. The fourth factor appeared to
represent

a processing speed factor with loadings from the two measures
of
processing efficiency and a smaller loading from the counting
working memory span task. The 0 – 4,000-ms forgetting rate
factor
showed some association with the storage-related factor (.27)
and
the processing-efficiency factor (�.35), which were themselves
correlated (�.45). However, the 4,000 – 8,000-ms forgetting
rate
factor showed little association with any of the other three
factors
(�.05, .05, and .05, respectively). The fact that the 0 – 4,000-
ms
and the 4,000 – 8,000-ms forgetting measures loaded on
different
factors suggests that they are not measuring the same
constructs.
Moreover, given that the 4,000 – 8,000-ms forgetting rate factor
showed no association with the other factors, which was
consistent
with the correlational analysis, this factor was not included in
any
further analyses.
To examine the extent to which the 0 – 4,000-ms forgetting rate
measures were associated with residual variance in working
mem-
ory span performance, which remained once variation associated
with processing efficiency and storage ability was removed, a
structural equation modeling analysis was performed. In this
model, we specified direct paths from three latent variables rep-
resenting forgetting rates (with loadings from the two 0 – 4,000-
ms
forgetting rate measures), storage ability (with loadings from

the
two storage tasks), and processing speed (with loadings from
the
two processing-efficiency tasks), respectively, to a fourth latent
variable representing working memory (with loadings from the
two working memory span tasks). Model fit was assessed using
a
combination of fit statistics. These indicated that the model pro-
vided a good fit to the data. More specifically, the chi-square
test
was nonsignificant, �2(14) � 15.45, p � .35, indicating that the
estimated covariance matrix was not significantly different from
the observed covariance matrix, and the root-mean-square error
of
approximation (RMSEA), which provides an estimate of the dis-
crepancy between the estimated and observed covariance
matrices,
was less than .05 (RMSEA � .03). In addition, the comparative
fit
index (CFI) and the goodness-of-fit index (GFI), which compare
the fit of the specified model to a baseline independence model,
were both above .95 (CFI � .99, GFI � .96). Parameter
estimates
for this model are presented in Figure 1. As shown in the figure,
both storage ability and processing speed significantly predicted
working memory (p � .05 in both cases), thus replicating the
findings of Bayliss et al. (2003) and showing that processing
efficiency and storage ability are important and distinguishable
constraints on children’s working memory span performance.
Im-
portantly, the path from the forgetting rate variable to the
working
memory variable was also significant (p � .05), indicating that
individual differences in forgetting rate are related to the
residual
variation in working memory span performance that remains

once
variation associated with the processing and storage operations
is
removed.
What Is the Nature of This Residual Variation in
Working Memory Span Performance?
To explore the nature of this residual variation in working
memory span performance in more detail, a series of
hierarchical
regression analyses were conducted. The analysis of the
forgetting
tasks reported above suggested that, as expected, the object for-
getting task involved more interference than the color forgetting
task, leading to more forgetting. Similarly, performance on the
second half of trials was worse than performance on the first
half
of trials, consistent with the suggestion that proactive
interference
constrained performance on the second half of each task. That
being the case, if the residual variance in working memory span
Table 2
Matrix of Pearson Correlation Coefficients for All Measures (n
� 88)
Target measure 1 2 3 4 5 6 7 8 9 10
1. Color forgetting rate 0–4,000 —
2. Color forgetting rate 4,000–8,000 �.20 —
3. Object forgetting rate 0–4,000 .53 .15 —
4. Object forgetting rate 4,000–8,000a .08 .27 �.06 —
5. Object working memory span �.41 .13 �.24 .08 —
6. Counting working memory span �.50 �.05 �.38 .07 .57 —
7. Digit span �.13 �.05 �.12 .03 .41 .37 —

8. Word span �.29 �.21 �.35 .00 .45 .45 .54 —
9. Object speed .23 .05 .31 �.01 �.27 �.42 �.22 �.24 —
10. Counting speed .32 .20 .24 .08 �.29 �.49 �.23 �.25 .54 —
Note. Correlations significant at p � .05 or above are presented
in bold.
a n � 87 for correlations involving this variable.
Table 3
Factor Loadings for the Exploratory Factor Analysis With
Oblique Rotation
Measure
Factor
1 2 3 4
Color forgetting rate 0–4,000 �.985 �.112 .016 .049
Color forgetting rate 4,000–8,000 .242 .976 �.252 .034
Object forgetting rate 0–4,000 �.477 .135 �.233 .019
Object forgetting rate 4,000–8,000 �.125 .320 .122 .021
Object working memory span .212 .212 .494 �.141
Counting working memory span .250 .042 .388 �.363
Digit span �.071 .030 .669 �.086
Word span .110 �.123 .754 .042
Object speed .038 �.050 �.042 .646
Counting speed �.008 .107 .076 .860
Note. Factor loadings greater than .32 are considered
meaningful
(Tabachnick & Fidell, 2007) and are presented in bold.
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performance reflects an executive factor associated with
maintain-
ing information in the face of interference from the processing
activity, then we might expect performance on the object forget-
ting task to be more closely associated with the residual
variance
than the color forgetting task and, consequently, to account for
more variance in working memory span performance. A similar
prediction can be made in relation to the buildup of proactive
interference, with performance on the second half of trials being
expected to account for unique variance over and above
variance
accounted for by performance on the first half of trials.
To examine the first of these predictions, the variance
associated
with the independent measures of storage ability and processing
efficiency was removed by entering the digit span measure and
the
task-specific measure of processing speed on the first step.
Then,
the order of entry of the 0 – 4,000-ms forgetting measures from
the

color and object tasks was systematically varied to identify the
unique contribution associated with each when entered on the
last
step. The results of this analysis are presented in Table 4. The
analyses revealed that the object forgetting measure did not
con-
tribute any additional variance to the object working memory
span
task, F(1, 83) � 0.03, p � .86, or the counting working memory
span task, F(1, 83) � 1.48, p � .23, over and above the
significant
contributions of the color forgetting measure. However, the
object
forgetting measure did contribute significant variance when en-
tered on the first step of the analysis for the counting working
memory span task, F(1, 84) � 9.06, p � .01. This indicates that
most of the variance (i.e., approximately 85%–100%) that the
object forgetting measure contributed to working memory span
performance was shared with the color forgetting measure.
To determine whether high proactive interference forgetting rate
trials were better predictors of residual variance in working
mem-
ory performance than low proactive interference forgetting rate
trials, a similar analysis was performed with the measures of
performance taken from the first half of trials (Low PI) and the
second half of trials (High PI) for each forgetting task. The
order
of entry of these measures was varied to identify the unique
contribution of each when entered on the last step. The results
of
this analysis are presented in Table 5. The analysis revealed that
the High PI variables accounted for significant variance when
entered on the first step of the analysis for the counting working
memory span task, F(2, 83) � 7.57, p � .01, and marginally

significant variance when entered on the first step of the
analysis
for the object working memory span task, F(2, 83) � 2.46, p �
.09. However, the High PI variables did not account for any
unique
variance over and above the Low PI variables for either the
object
working memory span task, F(2, 81) � 0.32, p � .73, or the
counting working memory span task, F(2, 81) � 1.32, p � .27.
Again, this indicates that most of the variance that the High PI
variables contributed to working memory span performance was
shared with the low PI variables (i.e., approximately 80%).
Discussion
This study was designed to (a) examine whether individual
differences in forgetting rate contribute unique variance to chil-
dren’s working memory span performance and (b) examine
poten-
tial sources of this variation by systematically manipulating
factors
thought to contribute to individual differences in the rate of for-
getting. In line with expectations, recall performance on the for-
getting tasks declined with increasing retention duration; recall
was poorer in the long-duration relative to the short-duration
conditions (cf. Towse et al., 2002). This indicates that the
forget-
Figure 1. Structural equation model and parameter estimates for
forgetting rate (FR), storage ability, and
processing speed predicting working memory (WM). The
numbers next to the single-headed arrows leading from
the latent variables to the observed variables are the
standardized factor loadings, and the single-headed arrows
leading from the FR, storage ability, and processing speed
variables to the WM variable are standardized

regression weights. The values next to the curved double-
headed arrows represent correlations, and the values
next to the small single-headed arrows leading to the observed
variables reflect the residual variance or
proportion of unexplained variance for each task. D1 represents
the disturbance term for the latent WM variable.
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CHILDREN
ting tasks, developed for use in this study, were successful at
inducing forgetting (see also, Ricker & Cowan, 2010). In
addition,
the factor analysis revealed that the measures of forgetting
taken
from these tasks were separable from measures of both storage
ability and processing speed. Consistent with this, individual
dif-
ferences in forgetting accounted for unique variance in working
memory span performance over and above variation associated
with the processing and storage operations involved in each
work-
ing memory span task. The fact that the two forgetting rate

estimates taken from the long retention intervals did not
correlate
with working memory span performance as strongly as the esti-
mates taken from the short retention intervals (see Table 2) sug-
gests that individual differences in forgetting rate may be best
captured within the early phase of the forgetting function. This
may be because the greatest loss of information appeared to
occur
during the first four seconds of each task (i.e., given that all
participants had perfect recall on the baseline measure; see
Table
1) and highlights the importance of measuring forgetting across
different retention intervals.
The findings from this study replicate and advance previous
research that identified unique contributions of processing effi-
ciency and storage ability to working memory span performance
(i.e., Bayliss et al., 2003, 2005) by demonstrating that the
residual
variance that remains once variance associated with these
compo-
nent processes is removed is more than just measurement error
and
instead is meaningful variation that can be captured and
described.
This finding is important because it provides evidence that
work-
ing memory span performance can be decomposed into a number
of separable factors and suggests that one of these factors is
associated with the rate at which individuals lose information
from
memory. Crucially, this rate of information loss is separable
from
the rate at which individuals perform the processing components
of the working memory tasks, and so, individual differences in
forgetting rate cannot be reduced to variation in basic speed of

processing.
The results of the factor analysis provide further support for
this
claim and are important for two reasons. First, they replicate
Bayliss and colleagues’ (2005) previous finding of separate pro-
Table 4
Unique Contributions of the Color and Object Forgetting Rate
Measures to Each Working
Memory Span Task
Step Variable(s) R2 Variable(s) R2
Object working memory span
1 Object speed, digit span .20�� Object speed, digit span
.20��
2 0–4,000 color forgetting rate .11�� 0–4,000 object forgetting
rate .02
3 0–4,000 object forgetting rate .00 0–4,000 color forgetting
rate .09��
Counting working memory span
1 Counting speed, digit span .31�� Counting speed, digit span
.31��
2 0–4,000 color forgetting rate .12�� 0–4,000 object forgetting
rate .07��
3 0–4,000 object forgetting rate .01 0–4,000 color forgetting
rate .06��
Note. The proportion of the variation that the object forgetting

measure contributed to working memory
performance that was also shared with the color forgetting
measure was estimated by subtracting the unique
variance accounted for by the object forgetting measure on the
last step of the regression analyses from the total
variance accounted for by the object forgetting measure on the
second step of the regression analyses and then
dividing the result by the total variance accounted for by the
object forgetting measure on the second step of the
regression analyses. For example, for the counting working
memory span task above, the resultant equation using
three decimal places would be .067 � .010 � .057; (.057/.067)
� 100 � 85%. A similar procedure was used
to calculate the proportion of shared variance for the proactive
interference measures shown in Table 5.
�� p � .01.
Table 5
Unique Contributions of the Proactive Interference Measures to
Each Working Memory
Span Task
Step Variable(s) R2 Variable(s) R2
Object working memory span
1 Object speed, digit span .20�� Object speed, digit span
.20��
2 Low PI color, low PI object .06� High PI color, high PI
object .05
3 High PI color, high PI object .01 Low PI color, low PI object
.02
Counting working memory span

1 Counting speed, digit span .31�� Counting speed, digit span
.31��
2 Low PI color, low PI object .11�� High PI color, high PI
object .11��
3 High PI color, high PI object .02 Low PI color, low PI object
.02
Note. PI � proactive interference.
� p � .05. �� p � .01.
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cessing and storage factors. Coupled with the finding that
process-
ing efficiency and storage ability each contribute unique
variance
to working memory span performance, these results again
suggest
that both factors need to be incorporated into any account of
working memory performance. Second, the finding that the for-
getting measures and the working memory span tasks load on

separate factors is intriguing given that both the forgetting tasks
and working memory span tasks could be thought to rely on the
same underlying mechanisms (Halford, Maybery, O’Hare, &
Grant, 1994; though see Jarrold, Tam, Baddeley, & Harvey,
2011)
and might have been expected to load together. The fact that
they
load on separate factors indicates that the contribution of the
forgetting measures to working memory span performance
cannot
be explained purely in terms of shared methodological variance.
Indeed, Jarrold et al. (2011) showed that the working memory
span
performance of a sample of adults differed from their
performance
on Brown–Peterson tasks, tasks that were similar in structure to
the
forgetting tasks used in the current study, in terms of both
overall
mean performance and the types of errors made. Intrusion errors
from prior lists occurred significantly more often in the Brown–
Peterson tasks, which is consistent with the view that proactive
interference, due to response competition between plausible re-
sponse alternatives, was operating in these tasks. In addition,
they
argued that this forgetting due to across-trial interference was
independent of the interference occurring between storage and
processing items within each trial of the working memory span
tasks, which they instead attributed to an overlap of representa-
tional features (cf. Nairne, 1990).
Taken together, the current findings indicate that children’s
working memory span performance can be decomposed into at
least three separable factors that individuals may vary on,
namely,
their storage ability, their general speed of processing, and the

rate
at which they forget information. The unique contribution of
processing speed is consistent with models of working memory
span performance in which individual or developmental differ-
ences in processing efficiency lead to variation in the time
during
which maintenance activities are prevented and forgetting can
occur (i.e., Barrouillet et al., 2004, 2007, 2009, 2012; Bayliss et
al.,
2005; see also Towse et al., 1998). Likewise, the unique contri-
bution of storage ability is consistent with models in which
indi-
vidual or developmental differences in reactivation rate
determine
the amount of information that can be successfully maintained
or
refreshed in any unoccupied time windows that occur during the
working memory span task (Barrouillet et al., 2009; Bayliss et
al.,
2005). Consistent with this argument, recent studies have shown
that older children are able to take greater advantage of any free
time during a working memory span task (Barrouillet et al.,
2009;
Gaillard et al., 2011; Tam et al., 2010). However, the novelty of
the current study is that we have identified a third constraint on
working memory performance that is separate from the
constraints
imposed by limitations in processing speed and storage ability.
This constraint is associated with an individual’s susceptibility
to
forgetting, that is, individual variation in the rate or degree to
which information is lost from memory when any form of main-
tenance activities is prevented. For example, one could imagine
two children who have similar processing speeds but vary in
terms
of their rate of forgetting. In the working memory span

paradigm,
both children would complete the processing activity of the task
in
a similar time, meaning that the time available for forgetting is
comparable. However, the child with the faster rate of
forgetting
would experience a greater loss of information during that time
relative to the other child, and consequently, their working
mem-
ory performance would be poorer. While previous researchers
have made suggestions along these lines (Barrouillet et al.,
2009;
Cowan et al., 1997; Hitch et al., 2001; Oberauer & Kliegl, 2001;
Portrat et al., 2009), this is the first study to show evidence
consistent with such a claim.
Moreover, the results of this study go some way toward speci-
fying the source of the residual variation in working memory
span
performance that is associated with forgetting. As expected,
recall
performance was poorer in the object relative to the color
forget-
ting task, suggesting that participants did experience more
inter-
ference in the object task, where the processing and storage
items
were both concrete nouns, than in the color task, where the
processing items were relatively distinct from the storage items
(cf.
Conlin & Gathercole, 2006; Jarrold et al., 2011). In addition,
consistent with the substantial evidence for proactive
interference
effects in Brown–Peterson paradigms (Crowder, 1989; Keppel &
Underwood, 1962), performance on the second half of trials was

poorer than performance on the first half of trials in the
forgetting
tasks. Given these findings, if variation in forgetting is due to
individual differences in the ability to resist interference either
within or across trials, then the contribution from trials
involving
more of these types of interference should be particularly
predic-
tive of working memory performance. However, the object
forget-
ting measure did not contribute any unique variance to working
memory span performance over and above that contributed by
the
color forgetting measure. Instead, between 85% and 100% of
the
variation in working memory span performance accounted for
by
the object forgetting measure was shared with the color
forgetting
measure. This finding provides little support for the claim that
one
of the important contributions to variation in working memory
span performance is from individual differences in an executive
ability associated with resisting interference from competing re-
sponse alternatives (see also Oberauer, 2009). Similarly, the
High
PI measures derived from each forgetting task did not contribute
any unique variance to working memory span performance over
and above the Low PI measures. Again, approximately 80% of
the
variation in working memory span performance accounted for
by
the High PI measures was shared with the Low PI measures.
Taken
together, these results do not appear to be consistent with the
controlled attention model of Engle and colleagues (i.e., Engle,

Kane, & Tuholski, 1999; Kane et al., 2001). In this model,
resist-
ing interference from response competition is a central function
of
the controlled attention or executive component of working
mem-
ory, with greater competition within a task context requiring
more
executive-attention resources for successful performance (Kane
et
al., 2007). The object forgetting task used in this study was
explicitly designed to capture individual variation in the ability
to
resist interference from response competition. The fact that per-
formance on this task did not contribute unique variance to
work-
ing memory performance, nor did a measure of performance
taken
under conditions of high proactive interference, presents a chal-
lenge for the influential and widely held view that individual
differences in the ability to resist interference moderate the
extent
of forgetting from working memory.
This begs the question of what is driving the variation in
forgetting captured by the tasks developed in this study. One
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CHILDREN
possibility is that individuals may vary in the rate at which
infor-
mation decays from memory during processing (Cowan et al.,
1997; Hitch et al., 2001; Oberauer & Kliegl, 2001). Indeed, the
finding of Cowan et al. (2000) that younger children showed a
greater loss of auditory sensory information over time than
older
children is consistent with this idea. Cowan et al. argued for the
recognition of attention-independent aspects of memory that
change with development. The variation in forgetting rates cap-
tured in the present study may indeed fall into that category and
could potentially be accommodated by the time-based resource
sharing (TBRS) model of Barrouillet and colleagues (2004,
2009).
In this model, processing and maintenance rely on a single
limited
attentional resource. Items that fall out of the focus of attention
suffer time-related decay but can be refreshed by a rapid
switching
of attention to the memory item. Thus, processing efficiency
and
rate of reactivation are important factors in this model.
Barrouillet
et al. (2009) also suggested that speed of decay may be another
potential factor contributing to developmental differences in
work-
ing memory but as yet have not explicitly included such a factor
in
the TBRS model. The recent study of Ricker and Cowan (2010)

also highlighted the need to incorporate a constraint on working
memory associated with loss of information over time, in
addition
to any effects due to the prevention of attentional refreshing or
reactivation. The results of the present study are consistent with
these ideas and suggest that a modification of the TBRS model
along these lines may be warranted.
An alternative possibility is that the variation captured by the
forgetting tasks does reflect an interference mechanism, but one
that is not related to executive functioning. Oberauer (2009) ex-
amined the mechanisms of interference involved in a working
memory span task by varying the similarity of the processing
and
memory items in various ways. While high phonological and
semantic similarity between processing and memory items did
not
impair recall performance relative to low similarity, high
phoneme
overlap and a fast pace of presentation did. Oberauer argued
that
these findings provided evidence for at least two mechanisms in
the working memory span task, one associated with the
distraction
of attention from maintenance activities, which we assume is
captured in our study by individual differences in processing
speed, and an interference mechanism associated with feature
overwriting (see also Jarrold et al., 2011; Oberauer, Farrell,
Jarr-
old, Pasiecznik, & Greaves, 2012; Saito & Miyake, 2004). As
the
processing and memory items used in the forgetting tasks in the
current study were all words, they are likely to share numerous
phonological features, and so, it is plausible that performance
on
the forgetting tasks reflects the degree of interference caused by

feature overwriting. Thus, the variation captured by the
forgetting
tasks in this study could readily be explained by individual
differ-
ences in a basic memory decay parameter or a form of
interference
associated with an individual’s susceptibility to feature overlap
between the processing and memory items.
Having said this, numerous studies have provided evidence of a
relationship between individual differences in working memory
and
the ability to resist interference (Kane & Engle, 2000;
Unsworth,
2010; see also Bunting, 2006; Gray, Chabris, & Braver, 2003,
who
showed a relationship between performance on trials subject to
inter-
ference from recent stimulus items and general fluid
intelligence), and
the suggestion in the current study that the residual variance in
working memory span performance may reflect a nonexecutive
factor
appears to be at odds with this earlier work. Three points are
relevant
to this issue. The first is to note that we have not explained all
of the
variation in working memory span performance, and so, we are
not
claiming that there is no executive contribution to working
memory
performance. It is always possible that a different measure of
execu-
tive functioning may explain some of this residual variance.
Second,

our study was conducted with a sample of children, and it is
possible
that the nature of the residual variance changes across
development.
Even though our previous work has shown remarkably similar
pat-
terns of relationships across both child and adult samples (e.g.,
Bayliss
et al., 2003), a replication of this study with an adult sample
would be
a worthy avenue for future research. Finally, it is likely that the
storage and processing operations that contribute to working
memory
performance require executive processes to some extent (see
Ang &
Lee, 2008; Miyake, Friedman, Rettinger, Shah, & Hegarty,
2001, for
evidence of this in relation to spatial short-term memory), and
so,
executive abilities may well contribute to individual differences
in
working memory. However, what we have shown is that
individual
differences in forgetting rates do account for significant
variance in
working memory span performance, independently of processing
and
storage, and that in contrast to what is typically assumed with
regard
to residual variance in working memory, this variation in
forgetting
rates may not be mediated by an executive ability. A second
point to
make is that one could argue that performance on both
forgetting tasks
requires some resistance to interference. Although the

executive-
attention account of working memory would presumably predict
that
the object forgetting task involves more response competition
than the
color task, if the color forgetting task does involve a degree of
competition between response alternatives, then performance on
this
task will still be affected by the ability to resist interference. It
then
follows that individual differences in an executive ability
associated
with resisting interference will be captured by measures taken
from
the color forgetting rate task as well. The fact that the object
task did
not contribute any unique variance in working memory
performance
over and above the color task could then be explained by
assuming
that individuals are resisting interference to the best of their
ability on
the color task. Consequently, while adding extra interference in
the
object task does produce a drop in memory performance overall,
it
would not necessarily influence the pattern of individual
differences
captured. Such a suggestion would leave open the possibility
that the
variance captured by the forgetting tasks is executive in nature
but
clearly depends on the assumption that individual differences in
the
ability to resist interference are maximized in the color
forgetting task

and that increasing the executive demands of a task does not
expand
these differences any further. The challenge that these data pose
to
proponents of an executive view of forgetting is whether this is
a
plausible suggestion and whether the variance captured by the
forget-
ting tasks, which is reliable and predictive of working memory,
can be
convincingly shown to be executive in nature.
In conclusion, the results of this study suggest that children’s
working memory performance is best understood in terms of a
num-
ber of separate abilities. That is, children may vary in terms of
their
processing speed, their storage ability, and the extent to which
they
suffer forgetting. The key finding of the current study is that
each of
these components can be reliably measured, and in doing so, we
have
begun to demystify the nature of the residual variation in
working
memory span performance that has commonly been attributed to
an
executive ability associated with controlling attention and
resisting
interference. In contrast to this view, the findings from the
present
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study suggest that at least some of the residual variance in
working
memory span performance may be best conceptualized as a
nonex-
ecutive parameter associated with forgetting. While the cause of
this
forgetting could readily be attributed to either time-based decay
or
interference due to feature overwriting, crucially, neither of
these
mechanisms necessitate any executive involvement. Whether
any
other executive abilities can explain some of the residual
variance in
working memory performance remains to be seen, but
irrespective of
this, current models of working memory that attribute residual
vari-
ance in working memory to an executive ability will need to
carefully
consider what it is that they are referring to as executive and
whether
the balance of evidence supports such a claim.
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Appendix
Memory Stimuli Used in the Object and Color Forgetting Tasks
Pool A Pool B
back men
room home
head face
night saw
door play
girl car
book land
bed line
road cold
sound drink
heat arm

touch fight
smile ball
dress shop
note step
lunch post
nose rain
dog camp
park shape
ring page
gun bag
date trip
bath fruit
lift coat
ship shirt
salt bird
pool band
goal knee
tape coach
jump soap
Received January 31, 2012
Revision received May 8, 2014
Accepted May 19, 2014 �
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CHILDREN
How Quickly They Forget: The Relationship Between
Forgetting and Working Memory
PerformanceMethodParticipantsDesignTasks and
ProcedureForgetting tasksWorking memory span tasksStorage
tasksProcessing-efficiency tasksResultsPreliminary
AnalysisForgetting TasksIs Performance on the Forgetting
Tasks Related to Residual Variance in Working Memory Span
Perfo ...What Is the Nature of This Residual Variation in
Working Memory Span Performance?DiscussionReferences
Article Summary Checklist
Basic APA format:
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