The development of two types of inhibitory control in

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C 2008 Cambridge University Press doi:10.1017/S1366728907003227
Bilingualism: Language and Cognition 11 (1), 2008, 81–93 The development of two types
of inhibitory control in
monolingual and bilingual
children∗
81
M I C H E L L E M . M A RT I N - R H E E
Harcourt Assessment/The Psychological Corporation
E L L E N B I A LY S TO K
York University
Previous research has shown that bilingual children excel in tasks requiring inhibitory control to ignore a misleading
perceptual cue. The present series of studies extends this finding by identifying the degree and type of inhibitory control for
which bilingual children demonstrate this advantage. Study 1 replicated the earlier research by showing that bilingual
children perform the Simon task more rapidly than monolinguals, but only on conditions in which the demands for inhibitory
control were high. The next two studies compared performance on tasks that required inhibition of attention to a specific cue,
like the Simon task, and inhibition of a habitual response, like the day–night Stroop task. In both studies, bilingual children
maintained their advantage on tasks that require control of attention but showed no advantage on tasks that required
inhibition of response. These results confine the bilingual advantage found previously to complex tasks requiring control over
attention to competing cues (interference suppression) and not to tasks requiring control over competing responses (response
inhibition).
Research by Bialystok and her colleagues has shown that
early bilingualism and constant daily use of two or more
languages leads to precocious development of certain cognitive processes for children (review in Bialystok, 2001),
advantages that persist across the lifespan (Bialystok,
Craik, Klein and Viswanathan, 2004; Bialystok, Craik and
Ryan, 2006). Importantly, these processing differences
between monolinguals and bilinguals are not confined
to linguistic tasks but have been found for a variety
of nonverbal problems, such as the paper-and-pencil
version (Pascual-Leone, 1969) of Piaget’s water level task
(Bialystok and Majumder, 1998), the dimensional change
card sort (DCCS; Zelazo, Reznick and Pinon, 1995)
examining knowledge–action differences in a classification task (Bialystok, 1999; Bialystok and Martin, 2004,
Study 1), the ability to see the alternate image in a
reversible figure (Bialystok and Shapero, 2005), and
the “reality question” in the appearance–reality problem
(Flavell, Flavell and Green, 1983, 1987), for which
the correct answer contradicts the current perception
(Bialystok and Senman, 2004). In all these studies, tasks or
conditions that were similar to the experimental conditions
but were not embedded in a misleading context that
created a conflict were solved equivalently by children
in both language groups.
* The research was funded by a grant from the Natural Sciences and
Engineering Research Council (NSERC) to the second author. We are
grateful to Jonathan Lipszyc for his assistance in Study 3.
The difference between children in the two language
groups in these studies was in their ability to resolve
perceptual conflict and respond on the basis of a nonsalient target cue. In the water level task, the angle of the
line defining the bottom of the beaker must be ignored in
order to draw a line perpendicular to the table to indicate
the gravitational horizontal; in the DCCS, the redness
of the stimulus that was just relevant for sorting and
provided the name, “the red one” must be overruled
to reinterpret the stimulus as “the round one”; in the
ambiguous figure reversal task, the interpretation of the
drawing as “duck” needs to be ignored in order to see
the same drawing as “rabbit”; and in the appearance–
reality problem, the perceptual cues that signal that the
object looks like a rock must be disregarded in order to
respond that the item is actually a sponge. Therefore, the
processing advantage for bilinguals occurs in problems
that require cognitive control to attend to the relevant
property and ignore a misleading property that is perceptually salient and presented with the target feature. This
ability to control attention is part of the executive function
that is developing gradually in preschool in children.
These results suggest that the development of executive
functioning broadly and inhibitory control in particular
is influenced by bilingualism. Children’s development of
inhibitory control is well documented (Diamond, 2002,
for review) and is a central feature of many theories
of cognitive development (e.g., Dempster, 1992; Tipper,
1992; Harnishfeger and Bjorklund, 1993; Diamond
Address for correspondence:
Ellen Bialystok, Department of Psychology, York University, 4700 Keele Street, Toronto, Ontario, M3J 1P3, Canada
[email protected]
82
M. M. Martin-Rhee and E. Bialystok
and Taylor, 1996). Moreover, inefficient inhibition has
been linked to such developmental psychopathologies
as attention deficit hyperactivity disorder, obsessivecompulsive disorder, Tourette syndrome, and autistic
spectrum disorder (Ozonoff, Pennington and Rogers,
1991; Ozonoff and Jensen, 1999). Therefore, if bilingualism influences the development of inhibitory control in
children, the results would be an important contribution
to understanding an essential developmental process.
The purpose of the present series of studies is to extend
these earlier results to provide a more precise measure
of inhibitory control and a more detailed interpretation
of potential processing differences between monolingual
and bilingual children. In these studies, the concept of
inhibitory control is examined through tasks that demand
different levels (Study 1) and types (Studies 2 and 3) of
inhibitory control.
The Simon task has been studied extensively, largely
as a measure of stimulus–response incompatibility,
but has also become the basis for a wide range of
research investigating attentional processes and executive
functions (Lu and Proctor, 1995). In a typical Simon
task, colored stimuli presented on the left or right side
of the display are associated with a left or right key
press. When the correct key press corresponds to the
position of the stimulus in the display, the trial is congruent
because both color and position information converge on
the same response; when the correct key and stimulus
position conflict, the trial is incongruent. In this case, the
position must be ignored because the correct response is
determined only by the color of the stimulus. The reliable
increase in response time to an incongruent trial relative
to a congruent trial is the Simon effect (Simon, 1969).
Although there is debate concerning the source of the
Simon effect, most investigators attribute it to conflict
during response selection. Once stimulus identification
has occurred (a red square), the response selection phase
ensues (hit left key). The Simon effect is the result of interference between the stimulus’ spatial code and the spatial
code of the associated response (Simon and Craft, 1970).
The Simon task meets the criteria for the type of
paradigm in which bilingual children have been shown
to outperform monolinguals. Two stimulus cues, one relevant but less salient, and one irrelevant but more salient,
compete for the child’s attention. To efficiently resolve the
conflict between the two cues, the more salient stimulus
feature must be ignored in favor of the less salient correct
option. Although the Simon paradigm has not been used
extensively with children, Diamond, O’Craven and Savoy
(1998) presented evidence from a directional Stroop task,
a paradigm similar to the Simon task. In that task, children
were told to press one key if a stimulus circle is shaded
and a different key if the circle is striped. The keys were at
opposite sides of the screen, and the stimuli were presented
on the right or the left of the screen, resulting in congruent
and incongruent trials as in the Simon task. The results
showed that children between the ages of 41/2 and 6 years
committed more errors and produced longer reaction
times to the incongruent trials than to congruent trials,
indicating a reliable Simon effect. There is evidence, however, that inserting a delay between stimulus presentation
and response simplifies tasks requiring inhibitory control
(Gerstadt, Hong and Diamond, 1994; Diamond, Kirkham
and Amso, 2002). On the DCCS and the day–night Stroop
task, the brief opportunity for reflection allowed children
to overcome the habitual response and perform correctly.
Therefore, children’s control over these processes can be
improved by reducing other task demands.
The Simon task has been used as a means of examining
executive function differences between monolingual and
bilingual adults. In research using young (20–30 years
old) (Bialystok, 2006), middle-aged (30–60 years old),
and older (60–80 years old) adults (Bialystok et al., 2004),
bilinguals completed the Simon task more efficiently than
monolinguals and demonstrated a smaller Simon effect.
However, in the study with young adults, faster bilingual
performance was only found for the most demanding
condition in which the stimuli created the most perceptual
conflict and the task imposed the greatest processing demands through the need for rapid switching between trials.
In the study with middle-aged and older participants, in
contrast, the bilinguals performed better than monolinguals in all conditions and the size of the advantage
increased with age, indicating a less severe decline in
performance with aging for the bilinguals. Importantly,
in all studies in which the bilinguals performed more
rapidly than the monolinguals, the difference was equally
significant for both congruent and incongruent trials. In
other words, the control processes required to perform
the Simon task are involved in all trials, not just those
explicitly containing conflict. This is likely because the
mixed blocks of congruent and incongruent trials that are
essential in presenting the Simon task require that the participant constantly hold the two rules in mind and anticipate switching between responses on each trial. Supporting
this interpretation, Lu and Proctor (2001) point out that the
irrelevant feature in mixed blocks influences responses in
all trials, including congruent ones. In a study using a behavioral version of an anti-saccade task, blocks with mixed
congruent and incongruent trials were performed more
rapidly by bilinguals than monolinguals with faster bilingual RTs on both types of trials, but blocks with single trial
types produced different results. In that case, monolinguals and bilinguals performed the same on blocks of congruent trials but bilinguals were faster than monolinguals
on blocks of incongruent blocks (Bialystok et al., 2006).
In young adults, reaction time differences are not
always evident in comparing performance across the
two language groups (Bialystok, 2006). In a study using
magneto-encephalography (MEG) with young adults
Inhibitory control
performing the Simon task, monolingual and bilingual
participants did not differ in the speed of response but
employed different frontal regions (Bialystok et al.,
2005). Specifically, the activation for the bilinguals
included regions overlapping with Broca’s area while
those for monolinguals did not. Again, the differences
between monolinguals and bilinguals were found equally
for congruent and incongruent trials of the Simon task.
Together, these studies show that the Simon task is
performed differently by monolinguals and bilinguals,
with more efficient performance by the bilinguals. The
present studies investigate whether these processing
differences are also found in children.
The present paper reports three studies in which the Simon paradigm was used to investigate executive functions,
in particular inhibitory control, in young monolingual
and bilingual children, and to identify the processes that
are different for children in these two language groups.
The primary hypothesis was that bilingual children will
perform the Simon task better than monolinguals as evidenced by faster reaction times. Following earlier research,
this advantage should be found for both congruent and
incongruent trials. Reducing the processing demands by
inserting a delay before responding should produce equal
performance by monolingual and bilingual children.
Study 1
The processing demands of the Simon task were manipulated by creating three versions of the task that differed
in the delay between the presentation of the stimulus and
the opportunity to respond. The delay reduces the saliency
of the misleading cue (Diamond et al., 2002) and should
therefore reduce as well the difference between children
in the two language groups. The prediction was that
bilinguals will outperform monolinguals in an immediate
response task, but a short delay will reduce the bilingual
advantage and a longer delay will eliminate it completely.
83
indicated that English was the main language spoken
between siblings in the home, but that the children were
read to and watched TV both in French and in English.
The experimenter was French–English bilingual, and in
addition to assessing their receptive vocabulary, conversed
with the children in both languages prior to testing to ensure competency in both French and English. According to
parental reports, all children were read to on a regular basis
and had similar exposure to television and films. All the
children lived in similar neighborhoods and had similar
social backgrounds. All the children were born in Canada
so there was no difference between children in the two
groups in immigration status. The only apparent difference was that the bilingual children spoke French at home.
Materials and procedures
FORWARD DIGIT SPAN. This test was used as an assessment
of short-term memory to ensure comparability of the
two groups. Children were presented with a random
string of digits and were required to repeat the string
back in the same order. The strings began with two
digits and increased by one digit every two trials. One
point was awarded for every correctly re-produced
sequence, producing the possibility for two points at each
string length. Testing ended when the child incorrectly
reproduced both sequences at a given string length.
PEABODY PICTURE VOCABULARY TEST REVISED (PPVTR). This task was used to compare the English receptive
vocabulary of the children in the two language groups.
Children were shown a plate consisting of four pictures
and pointed to the one named by the experimenter.
Testing continued until children made six errors in eight
consecutive trials. The number of correct responses is
calculated as the raw score, and converted to a standard
score by means of age-related norms.
Method
EĢCHELLE VOCABULAIRE EN IMAGES PEABODY (EVIP).
This is a standardized test of receptive vocabulary in
French and was administered to the bilingual children.
The testing procedures and scoring criteria are the same
as those for the PPVT English test.
Participants
There were 34 children, half of whom were monolingual.
The monolinguals (6 boys and 11 girls; mean age 4;7
years) were English-speaking children recruited from
childcare centers. The bilingual children (8 boys and 9
girls; mean age 5;0 years) were fluent speakers of French
and English recruited from after-school programs within a
French school board. The French school system provides
instruction exclusively in French to children who typically
speak French at home to at least one parent. English is not
introduced into the curriculum until the third grade, when
children are eight years old, although children are exposed
to English during extracurricular activities, such as sports
teams or classes. All parents of the bilingual children
SIMON TASK. The Simon task was instantiated on an
IBM laptop computer. Children were instructed to press
the red button if a red square appeared and the blue button
if a blue square appeared. The left and right shift keys were
labeled with a red sticker and a blue sticker respectively.
Half the trials were incongruent, so the colored square
appeared on the side opposite to the appropriate shift key.
Three versions of the Simon task were administered
to children. In the immediate task, the child was told
to respond as quickly as possible when the stimulus
appeared. Trials timed out after 5000 ms and the next
trial appeared, leaving any missed trial as an error. In the
two delay tasks, children were told they could not respond
until a cue appeared. In the short delay task, the cue was
84
M. M. Martin-Rhee and E. Bialystok
presented 500 ms after the stimulus and remained on the
screen for 800 ms, and in the long delay task the cue
appeared after an interval of 1000 ms. The response could
be made as soon as the cue appeared but prior to that point
the response keys were locked. The cue was an icon of a
hand shown in the middle of the screen with the first finger
pointing downwards. The child was instructed not to press
any button while waiting for the cue. Each task was administered separately with its own set of instructions and
preceded by four practice trials. Children were required
to achieve 100% accuracy on the practice trials before
proceeding to the experimental trials for each task. The
tasks were presented in the fixed order described above.
Results
The mean score on the forward digit span was 6.1
(SD = 1.3) for the monolingual children and 5.9
(SD = 1.7) for the bilingual children, a difference that
was not significant, t < 1. In contrast, the monolinguals
obtained a mean score of 111.4 (SD = 10.9) on the
PPVT-R standard score and the bilinguals obtained a
mean score of 89.6 (SD = 24.4), which was significant,
t(32) = 3.36, p < .01. A paired-samples t-test indicated
that the bilingual children’s scores on the English
PPVT-R (M = 89.6, SD = 24.4) and on the French EVIP
(M = 98.8, SD = 14.8), t(17) = 1.36, n.s., were equivalent.
Children made very few errors in the three Simon
tasks, with the mean percentage of errors ranging from
2% to 5%. There were no differences between groups
in error rate on any of these tasks, all Fs < 1. The mean
RT for the correct trials in each of the Simon tasks is
presented in Figure 1. There was not sufficient power
in the design for the three tasks to be analyzed together
(because of the sample size, the number of conditions,
and the number of trials in each condition) so given the
different hypotheses for each task, a two-way analysis
for language group and congruence was conducted
separately for each. In the immediate task, congruent
trials elicited faster reaction times than incongruent trials,
F(1, 32) = 4.19, p < .05, and bilingual children responded
more rapidly than monolinguals, F(1, 32) = 7.40, p < .01,
with a power of .71. There was no language group by trial
type interaction, F < 1, indicating that the reaction time
difference between congruent and incongruent trials was
the same for both language groups. In both the short delay
and long delay tasks, there were no differences between
congruent and incongruent trials, and no differences
between monolingual and bilingual children, all Fs < 1.
Another way to consider performance is to calculate
the Simon effect, namely, the RT difference between
congruent and incongruent trials. In spite of large
differences in this value, the difference between groups
was not significant for any of the tasks. For the immediate
task, the monolinguals (M = 264, SD = 881) and
bilinguals (M = 306, SD = 739) did not differ, F < 1;
2500
2000
1500
1000
500
0
Congruent
Monolingual
Incongruent
Bilingual
Figure 1a. Reaction times in ms and standard deviations on
the Immediate Response task by language group and trial
type in Study 1.
2500
2000
1500
1000
500
0
Congruent
Monolingual
Incongruent
Bilingual
Figure 1b. Reaction times in ms and standard deviations on
the Short Delay Response task (500 ms) by language group
and trial type in Study 1.
2500
2000
1500
1000
500
0
Congruent
Monolingual
Incongruent
Bilingual
Figure 1c. Reaction times in ms and standard deviations on
the Long Delay Response task (1000 ms) by language group
and trial type in Study 1.
for the short delay task, the monolinguals (M = 77,
SD = 701) and bilinguals (M = 412, SD = 1159)
produced a larger gap but were still not significantly
different, F(1,32) = 1.08, n.s., and for the long delay task,
the monolinguals (M = 72, SD = 790) and bilinguals
(M = 43, SD = 719) again produced similar results, F < 1.
Discussion
Monolingual and bilingual children performed the same
on a simple test of memory span, but monolinguals scored
Inhibitory control
higher on a standardized measure of receptive vocabulary.
This difference in vocabulary size is commonly found for
monolingual and bilingual children (review in Oller and
Eilers, 2002). Moreover, the vocabulary score in English
and French was the same for the bilingual children,
supporting the claim that they were balanced bilinguals.
The bilingual children performed the immediate Simon
task more rapidly than monolingual children. In contrast,
the children in the two groups performed equivalently
when a delay allowed them to reflect briefly on the
response, so there were no group differences in either the
short delay or long delay tasks. Although it was hypothesized that the short delay would reduce the bilingual advantage without eradicating it, both delays were long enough
to allow all the children to resolve the perceptual conflict.
The bilingual advantage in the immediate task was
found for both the congruent and incongruent trials,
replicating the pattern in our previous research with
the Simon task (e.g., Bialystok et al., 2004, 2005). The
consistency of the group responses to both types of
trials was confirmed by the lack of significant group
differences for the Simon effect in any of the tasks. Even
though the absolute size of the Simon effect appeared to
be different for the two groups, especially in the short
delay condition, the small sample size and large variance
prevented any such differences from being considered
significant. For these reasons, it is especially notable that
the group difference in reaction time for the immediate
task emerged as strongly reliable.
Study 2
The results of Study 1 add to our previous evidence for
bilingual advantages in the Simon task without identifying
the source of that advantage. An important distinction
between types of inhibitory control has been proposed by
Bunge and her colleagues (Bunge, Dudukovic, Thomason,
Vaidya and Gabrieli, 2002). The distinction is based on the
difference between bivalent displays which are comprised
of two potentially conflicting dimensions, and univalent
displays in which only a single feature is presented. The
two features of bivalent displays can either converge on
a single response, creating congruent trials, or conflict
by indicating different responses, creating incongruent
trials. Bunge et al. (2002) call the inhibition required in
this case “interference suppression”. In univalent tasks,
the conflict is between two response options to the same
stimulus feature, creating a conflict between the habitual
response and a less familiar arbitrary response that must
override and replace it. According to Bunge et al., these
problems require “response inhibition”. Bunge et al.
(2002) have demonstrated that each of these kinds of
inhibition shows a different developmental trajectory and
engages different areas of the prefrontal cortex.
This distinction between interference suppression and
response inhibition is useful for identifying potential
85
processing differences in inhibitory control between
monolingual and bilingual children. For bilinguals,
their two linguistic systems function as bivalent
representations, offering different, potentially competing
response options to the same intention or goal. To manage
this conflict, bilinguals must attend to the relevant
language system and ignore the unwanted system to
assure fluency in speech production (e.g., Kroll and
Stewart, 1994; Green, 1998; La Heij, 2005). This is
comparable to the Simon task in which bivalent displays
require children to attend to one feature (color) and
ignore the other (position). Therefore, tasks requiring
interference suppression to selectively attend to one of
two stimulus cues should be solved better by bilinguals.
The inhibition associated with univalent displays
seems to be less relevant to the bilingual experience.
Bilinguals do not REFRAIN from speaking in the manner
indicated by response inhibition, but must select
between two competing linguistic systems for language
production. Further, Costa, Miozzo and Caramazza
(1999) have shown that there is no evidence that the
unwanted language is actually inhibited in the sense of
becoming unavailable. Therefore, there is no reason to
expect a bilingual advantage on tasks assessing response
inhibition to univalent displays. However, in a previous
study, younger and older adults who were monolingual
or bilingual performed in a behavioral version of an
anti-saccade task, in which anti-saccade trials constitute a
univalent condition. The task is to avoid responding on the
side in which a target is flashed and replace that habitual
response by responding on the OPPOSITE side. Young
monolinguals and bilinguals performed equivalently, but
older bilinguals (approximately 65 years old) were more
able than older monolinguals to override the habitual
response in those trials (Bialystok et al., 2006). Therefore,
the prediction is that there is no reason to expect a bilingual
advantage in responding to univalent task conditions, but
there may be factors that mitigate that prediction.
Most of the research comparing executive processing
by monolinguals and bilinguals has been based on bivalent
displays and the need for interference suppression. The
present study includes a task based on response inhibition
with univalent displays. Performance on the standard
condition of the Simon task using immediate response
and more trials than in Study 1 and on a modification of
the day–night Stroop task (Gerstadt et al., 1994; Diamond
et al., 2002) is compared to assess the relation between
these two aspects of inhibitory control in young children
who are monolingual or bilingual. The hypothesis is
that bilinguals will outperform monolinguals on tasks
using bivalent displays (both congruent and incongruent
trials in the Simon task) because these tasks mirror the
processing required to manage two language systems, but
monolinguals and bilinguals will perform the same on
tasks using univalent displays (Stroop picture naming)
because these do not obviously correspond to the kind
86
M. M. Martin-Rhee and E. Bialystok
of inhibitory control used in managing two language
systems.
Method
Participants
There were 41 four-year-old children, including 20
monolinguals and 21 bilinguals, involved in the study.
The monolingual children (10 boys, 10 girls; mean age 4;
5 years) understood and spoke only English. The bilingual
children (12 boys, 9 girls; mean age 4;6 years) had three
different backgrounds. Fourteen of these children were
French–English bilinguals recruited from after-school
programs in the French school board, as in Study 1.
In addition, four Chinese–English and three Spanish–
English bilinguals were recruited from the same daycare
as the monolingual children. These children are exposed
entirely to English at daycare but speak Chinese or
Spanish at home. There was no difference between the
results of the 14 French–English bilinguals and the seven
remaining bilinguals, so no distinction between them is
made in the presentation of the results.
Materials and procedure
The Forward Digit Span and Peabody Picture Vocabulary
Test-Revised (PPVT-R) were used following the same
procedures as in Study 1.
SIMON TASK. This task was instantiated on a Dell laptop
computer using DMDX software. Blue and red squares
were presented on either side of the computer screen,
centered between the top and bottom. The instruction was
to press the blue button when a blue square appeared and
the red button when a red square appeared. The right and
left shift keys were marked with a blue and red sticker,
respectively.
The experimenter explained the instructions to the
child, followed by a set of 8 practice trials. If the child
made more than 2 errors on these practice trials, the
instructions and all 8 trials were repeated until children
reached this criterion level. The task consisted of 40
experimental trials with a brief break after 20 trials. Each
trial began with a cross fixation for 500 ms, followed by
the stimulus, which remained on the screen for 5000 ms,
or until the child responded. Due to an error in the
programming of the task, there were 19 incongruent trials
and 21 congruent trials.
STROOP PICTURE NAMING TASK: The task was adapted
from one developed by Gerstadt et al. (1994). The child is
told to say “night” when presented with a picture showing
a bright sun and to say “day” when shown a picture of a
dark moonlit sky. There is no conflict between competing
perceptual cues (because each picture only shows one
kind of display) but there is a need to overcome the
habitual response which is to name the display.
This was also instantiated on a Dell laptop computer
using DMDX software and voice response technology.
The verbal response is recorded into a wave file for each
trial. Response accuracy was determined by listening to
each wave file and manually recording the response as
correct, incorrect, or incomprehensible. Response latency
was recorded from the onset of the stimulus to the onset
of the child’s voice.
There were two conditions used in this task, day–night
and cat–dog, with two trial types for each, same name
and opposite name. In the same name trials, children
named the picture as quickly as possible, and in the
opposite name trials, gave the name of the other picture,
for example, “day” for the picture of night, and “night” for
the picture of day. Children were told to answer as quickly
as possible without making errors. The task was explained
using laminated cards depicting the pictured stimuli. Four
computerized practice trials preceded the start of the experimental trials. The practice trials repeated until children
demonstrated 100% accuracy. The image remained on the
screen for 2000 ms, regardless of whether the child had
responded. Each condition was presented in two blocks of
24 trials each, one consisting of same name trials and the
other of opposite name trials. The order of the conditions
(day–night and cat–dog) was counterbalanced across
children, but same name trials were always presented first.
Results
The mean score on the forward digit span was 5.5 for
children in both groups, t < 1. The mean PPVT standard
score was 96.4 for the monolinguals (SD = 15.0) and
86.4 for the bilinguals (SD = 15.6), a difference that was
significant, t = 2.08, p < .05, as in Study 1.
The mean percentage of errors on the Simon task
ranged from 5% to 15%, with no difference between
groups, F(1, 39) = 1.68, n.s. However, more errors were
committed in the incongruent (13%) than congruent (8%)
trials, F(1, 39) = 73.26, p < .0001, with no interaction
between language group and congruence, F < 1. The
mean reaction times for the correct trials in the Simon task
are plotted in Figure 2 by trial type and language group.
A two-way ANOVA revealed a main effect of trial type,
where congruent trials elicited faster response times than
incongruent trials, F(1, 39) = 52.97, p < .0001. There
was a main effect of language group, in that bilingual
children responded more rapidly across both trial types
than monolingual children, F(1, 39) = 4.19, p < .05, with
a power of .55, and no group by trial type interaction, F(1,
39) = 2.17, n.s. The Simon effect was 185 ms (SD = 140)
for monolinguals and 122 ms (SD = 131) for bilinguals,
a difference that was not significant, F(1,39) = 2.17,
p = .14. There were no speed-accuracy trade-offs in
performance, all rs < .15.
Inhibitory control
87
2000
Mean RT (ms)
1800
*
1600
*
1400
1200
1000
800
600
Congruent
Incongruent
Trial type
Monolingual
Bilingual
* Denotes significant differences
Figure 2. Reaction times in ms and standard deviations on the Simon task by language group and trial type in Study 2.
The accuracy scores for the picture naming task
were analyzed in a three-way ANOVA for condition,
trial type, and language group. There were no effects
of condition (day–night = 87% correct; cat–dog = 86%
correct) or language group (monolinguals = 87% correct;
bilinguals = 89% correct), but there was a main effect of
trial type in which the opposite name blocks (M = 84%
correct) were more difficult than the same name blocks
(M = 89% correct), F(1, 37) = 4.29, p < .05 for both
tasks. There was no condition by language group
interaction, F < 1.
Because of the sensitivity of the voice response
technology, loud noises such as school bells, laughing, or
coughing often interfered with the voice onset, so these trials were deleted when they were checked against the wave
file. Approximately 30% of the RT data were eliminated
for this reason so the analyses should be interpreted
with caution. The remaining RT data were analyzed
in a three-way ANOVA for condition, trial type, and
language group. There were no differences for condition
(day–night = 858 ms, cat–dog = 803 ms; F = 1, n.s.), trial
type (same name = 822 ms, opposite name = 841 ms;
F < 1, n.s.), or language group (monolingual = 870 ms,
bilingual = 798 ms; F = 1.93, n.s.), and no interactions
between any of the factors. There was no correlation
between the RT and the accuracy score for any condition
in this task, all rs < .19, ruling out speed-accuracy tradeoff
as a factor in performance.
Discussion
Bilingual children who were comparable to monolingual
children on a measure of short-term memory but less
proficient in English receptive vocabulary were faster to
respond on both congruent and incongruent trials of the
Simon task, replicating the results of Study 1. The greater
number of trials in this study reduced the mean RTs
overall, but the difference between the language groups
remained. In contrast, there was no difference between the
two groups on either the response latencies or accuracy
scores in the Stroop picture naming task. This pattern
confirms the prediction that the processing demands of the
Simon task and Stroop naming task are different and that
bilingual children show an advantage only in the former.
It is possible that the bilingual children faced an
additional challenge in the univalent task because
the response was based on rapid retrieval of a verbal
label. In both studies, the bilinguals scored lower than
monolinguals on the test of receptive vocabulary. More
importantly, however, bilinguals have been shown to be
slower than monolinguals in rapid picture naming, and
also experience more frequent tip-of-the-tongue states
88
M. M. Martin-Rhee and E. Bialystok
than monolinguals (Gollan and Kroll, 2001; Gollan and
Silverberg, 2001). Therefore, the equivalent performance
by monolinguals and bilinguals in the univalent task based
on picture naming may mask an underlying difference
between the groups in response inhibition. In other words,
a potential bilingual advantage in response inhibition may
have been mitigated by a bilingual disadvantage in lexical
retrieval. This possibility was examined in the next study.
Study 3
To control for the role of facility in lexical access, the
Simon task was adapted to create bivalent and univalent
displays that did not rely on verbal ability. The stimuli
were directional arrows instead of colored squares. In
the bivalent condition, an arrow appeared on one side
of the screen and children pressed the key to indicate
the direction in which the arrow was pointing; in the
univalent condition, an arrow appeared in the center of
the screen and children pressed the key to indicate either
the same direction the arrow was pointing or the OPPOSITE
direction. In both conditions, the stimuli are identical,
except for their location on the computer screen. The first
condition corresponds to the standard bivalent Simon task
and the second parallels the demands of the univalent
Stroop naming task. If there is a bilingual advantage for
interference suppression, as indicated in Studies 1 and
2, then bilinguals will again respond more rapidly than
monolinguals on the congruent and incongruent trials of
the bivalent conditions. If there is a bilingual advantage
in response inhibition, contrary to the results of Study 2,
then bilinguals will also respond more rapidly than monolinguals on the opposite trials in the univalent condition.
Method
Participants
In the previous studies, the children were about 41/2 years
old, and although they could perform the task to a high
level of accuracy, they produced long RTs with large
variances. Therefore, Study 3 examined children who
were slightly older in order to observe whether there
were performance differences between monolinguals and
bilinguals a few years later when response times were
more stable.
There were 32 participants with a mean age of 8;0
years. The monolingual and bilingual children attended
the same school and lived in the same neighborhood.
The school provided two hours of instruction each day in
Hebrew to all the students. The monolingual students were
those who did not use Hebrew outside the classroom and
never used it for conversational purposes. In spite of some
formal study of Hebrew, their proficiency in the language
was extremely limited and the language was essentially
never used for communication. This group consisted of
19 children (10 boys, 9 girls). The bilingual children
were those who spoke another language at home. There
were 13 children (5 boys, 8 girls) in this group, of whom
nine spoke Russian and four spoke Hebrew. The bilingual
children were completely fluent in both languages and
used both languages every day. Some of these children
were born outside Canada and immigrated as very young
children with their families. However, there were no
apparent social, educational, or cultural differences that
distinguished between the children in the monolingual
and bilingual groups. The primary factor determining
membership in the two language groups was the children’s
knowledge and use of a non-English language.
Materials and procedures
CORSI BLOCKS (CORSI, 1972). This task is used to measure
short-term spatial capacity (Kolb and Wishaw, 2001).
Children are shown a set of eight blocks arranged in
an uneven pattern fixed to a platform. The experimenter
points to a predetermined sequence of the blocks, and
the child is required to point to the same blocks in the
same order. Testing begins with a series of two blocks
and increases by one block after every two trials; testing
ends when the child is incorrect on both trials of the same
sequence length. The scores were calculated in terms of
correct adjacent pairs. A child was awarded one point for
every correctly identified block, provided it was adjacent
to another correctly identified block. For example, if the
sequence was 4 2 6 5 7, and the child pointed to 4 6 2 5 7,
the child was awarded two points, one each for the 5 and 7
blocks. If the sequence was 4 2 8 6 3, and the child pointed
to 4 2 8 5 7, the child was awarded three points.
PEABODY PICTURE VOCABULARY TEST III. This is a more
recent version of the same receptive vocabulary test used
in Studies 1 and 2. The procedures and scoring system
are the same as those used for PPVT-R.
UNIVALENT AND BIVALENT ARROWS TASK. This task was
instantiated on a Dell laptop computer and programmed in
Superlab software. One mouse was fixed to each side of the
computer display, and the left key on each mouse was the
response button. Each mouse was mounted on a black platform that covered the laptop’s keyboard and anchored at
either end to align it with the left or right end of the screen.
In the univalent arrows task, a black arrow on a white
background appeared in the center of the screen and
children pressed a key indicating either the direction
the arrow was pointing (same direction condition) or the
opposite direction (reversal condition). These conditions
were presented in separate blocks of trials. The instructions were presented on the screen with examples, and the
experimenter read the instructions to the child. There were
8 practice trials with feedback before each block. Trials
began with a 150 ms inter-stimulus interval (ISI) followed
by presentation of the arrow in the center of the screen
Inhibitory control
89
1000
Mean RT (ms)
900
800
700
600
500
400
Same Direction
Reversal
Condition
Monolingual
Bilingual
Figure 3. Reaction times in ms and standard deviations on the univalent Arrows task by language group and condition in
Study 3.
that remained until a response was made. Children were
told to go as fast as possible without making mistakes.
There were 24 same direction trials and 48 reversal trials,
half of which pointed to the right and half to the left.
For the bivalent Simon arrows task, the arrow appeared
at one side of the screen and the instruction was to press the
mouse button showing the direction the arrow was pointing. Half of the trials were congruent because the stimulus
position and direction corresponded and half were
incongruent where the position and direction conflicted.
There were 12 practice trials with feedback. If more than
3 mistakes occurred, then the instructions and practice
trials were repeated. The experimental block began with
a 150 ms ISI, followed by presentation of the stimulus,
which remained on the screen until a response was made.
There were 48 trials of which half were congruent and half
incongruent, presented in random order within the block.
Results
The mean score on the Corsi blocks for the monolingual
children was 32.47 (SD = 10.39) and for the bilingual
children, 36.08 (SD = 11.69), a difference that was not
significant, t < 1. The standard scores on the PPVT-III
were 100.89 (SD = 12.15) for the monolingual children
and 95.53 (SD = 8.45) for the bilinguals, but this was
not significant, t(32) = 1.47, p = .18. It is possible that
vocabulary gap has begun to close for children of this age.
The mean percentage of errors in the univalent task
ranged from 3% to 6%, with no differences between
condition or language group, and no interaction. For
the bivalent task, the mean percentage of errors ranged
between 3% and 8%, with fewer errors on the congruent
trials (4%) than incongruent trials (7%), F(1, 29) = 16.83,
p < .0003. However, there was no difference between the
language groups and no interaction, Fs < 1.
The mean RTs for the univalent arrows task are plotted
in Figure 3. Response latencies were analyzed with a
two-way ANOVA for condition (same direction, reversal)
and language group. The same direction responses
(603 ms, SD = 148) were faster than reversal responses
(766 ms, SD = 189), F(1, 29) = 54.16, p < .0001, with
no effect of language group, F < 1, and no interaction of
condition and language group, F(1, 29) = 2.62, p = .12.
Figure 4 depicts the RTs in the congruent and incongruent trials of the bivalent Simon arrows task by language
group. A two-way ANOVA revealed a significant effect of
trial type, F(1, 29) = 24.37, p < .0001, as congruent trials
were faster than incongruent trials, and language group,
F(1, 29) = 5.95, p < .02, showing faster responding by
the bilingual children, with no interaction, F(1,29) = 1.48,
n.s. This was confirmed by calculating the mean Simon
effect for children in the two groups. This score was not
different for the monolingual (M = 113, SD = 113) and
bilingual (M = 65, SD = 95) children, F(1,30) = 1.48, n.s.
Finally, there was no significant correlation between errors
and RT for any of the conditions, all rs < .15, so there was
no speed-accuracy tradeoff.
Discussion
The results of the present study replicate those of Study
2 using tasks that removed the demands for verbal
90
M. M. Martin-Rhee and E. Bialystok
1100
*
Mean RT (ms)
1000
*
900
800
700
600
500
400
Congruent
Incongruent
Trial type
Monolingual
Bilingual
* Denotes significant differences
Figure 4. Reaction times in ms and standard deviations on the bivalent Simon Arrows task by language group and trial type
in Study 3.
proficiency. The bilingual children responded more
rapidly than the monolinguals in the Simon arrows
task, which consisted of a bivalent display requiring
interference suppression, but not in the univalent
direction task, which consisted of a univalent display
requiring response inhibition. The task effects were as
expected: Congruent trials were faster than incongruent
for the bivalent task and same direction responses
were faster than reversal responses for the univalent
task. Nonetheless, bilingual children completed the
bivalent task more easily than the monolinguals. Also
replicating previous results, the faster response times for
the bilinguals were found equally for the congruent and
incongruent trials. The children in this study were almost
four years older than those in the previous two studies,
better matched on vocabulary levels, and produced faster
and more stable response times with smaller variance.
General discussion
In three studies, a reliable advantage for bilingual children
was found on the Simon task under a specific set of task demands. The main criterion for demonstrating this bilingual
advantage is that the task is based on a bivalent display in
which two presented features potentially indicate different
responses. Efficient performance requires resolving the
contradictory response cues while holding two possible
response options in mind through a set of mixed trials. For
example, to perform efficiently on the incongruent trials,
children must control attention to the color of the square
(Studies 1 and 2) or direction of the arrow (Study 3) and
ignore the position of the stimulus on the screen. This is
a challenge for all children, and incongruent trials always
produced longer response latencies than congruent trials.
The need to respond immediately upon seeing the
stimulus increases the demands of the task because the
perceptual competition between the two cues is enhanced.
The task becomes simpler if a delay is imposed between
the stimulus and response because it offers the child some
time to resolve the competition, resist the immediate
association, and respond in a more controlled manner.
This manipulation made the task easier, and performance
was similar for all the children in the two delay tasks.
Therefore, the differences between the monolinguals and
bilinguals in this type of conflict task based on interference
suppression occur at an early stage of processing
and are probably associated with the initial ability to
control attention to complex stimuli. This supports the
interpretation that the irrelevant spatial information in the
Simon task is processed immediately (Hommell, 1994).
For these reasons, bilinguals outperformed monolinguals on the immediate Simon task. The bilingual
advantage, however, was found equally for congruent
and incongruent trials, as in our previous research (e.g.,
Bialystok et al., 2004), but unlike the results with adults,
the size of the Simon effect was the same for all the
children. Regarding the first, point, the majority of our
research with these conflict tasks that are presented mixed
block trials have produced bilingual advantages for both
trial types, making these results consistent with previous
Inhibitory control
research. The second point about the relative size of
the Simon effect is less clear. One possibility is that the
longer latencies required by children to respond diminish
the importance of the difference between congruent and
incongruent latencies as a proportion of overall response
time. In other words, because the latencies are long,
the differences between latencies, and by extension, the
variance associated with those RTs, are not sufficiently
sensitive to detect differences between groups. Another
consequence of this finding is that it is unlikely that the
bilingual advantage is simply or exclusively in some
aspect of inhibition but more likely in the ability to
monitor competing cues over a set of conflicting trials
and direct attention appropriately for the response.
In contrast to these tasks, those based on univalent
displays require overriding a habitual or familiar response
to a stimulus and replacing it with a contrary response.
This type of control, response inhibition, is concerned
less with attentional control and more with the execution
of motor responses to familiar stimuli. These tasks
were solved equivalently by children in both language
groups. Nothing in the bilingual experience appears to
benefit children in demonstrating this type of inhibitory
control. In Studies 2 and 3, monolinguals and bilinguals
performed equivalently on such a task. In a previous study,
however, older bilinguals outperformed monolinguals on
an anti-saccade type task that required a key press to a
position opposite to one that had been cued (Bialystok
et al., 2006). Two factors can explain this disparity. First,
it was shown in Study 1 that changes in task demands
that affect the degree of conflict influence the relative
performance between the groups. The stimuli used in
the study by Bialystok et al. (2006) consisted of rapidly
flashing target cues on one side of the display monitor,
and this is presumably a more compelling cue to attract
attention to one side than is a directional arrow passively
pointing one way or the other. Second, the older adults
who were the participants in the study by Bialystok et al.
(2006) had reduced resources for executive processing,
a normal consequence of aging (Daniels, Toth and
Jacoby, 2006). This reduction in resources enhances
the processing demands of the task and increases the
relative advantage of the bilinguals. As shown in other
research, the decline of executive processing in aging is
reduced for bilinguals (Bialystok et al., 2004). Therefore,
the expectation is that there is a bilingual advantage in
response inhibition only when processing demands of the
task are particularly high or processing resources of the
participants are particularly low. Otherwise, monolinguals
and bilinguals solve these problems equivalently.
It is tempting to believe that the bilingual advantage
found in these three studies is not due to the language
experience of these children but to some other factor that
may be correlated with bilingualism. For example, it is
well known that socioeconomic status affects children’s
91
abilities in these types of tasks (e.g., Rescorla, 1989;
Arriaga, Fenson, Cronan and Pethick, 1998). However,
there is no evidence that the socioeconomic status of the
children in the two groups tested in the present studies
was different. All the children were selected from demographically equivalent areas of the city and in many cases
attended the same schools. Moreover, the young bilingual
children in Studies 1 and 2 scored significantly below
the monolinguals on a measure of receptive vocabulary,
indicating that if different at all, their English language
skills were inferior to those of the monolingual children.
In most cases, the children were born in the same country
– only a few of the children in Study 3 were immigrants.
The non-English language spoken by the bilinguals across
three studies – French, Chinese, Spanish, Hebrew, and
Russian – never made any difference in the results. Finally,
the monolingual and bilingual children across all three
studies achieved comparable scores on rough measures of
short-term memory. Therefore, there is no evidence that
some factor other than bilingualism is responsible for the
group differences found in the three studies.
The participants in the three studies were different in
several ways – the bilinguals in the three studies spoke
different home languages and the children in Study 3 were
older than those in the first two studies. More importantly,
the monolinguals in Study 3 were receiving formal
classroom instruction in another language, although
they did not use that language for conversation. In that
sense, these children had some knowledge of another
language but were functionally monolinguals. In spite of
these differences, the pattern of results were identical:
all the bilingual children performed more efficiently than
monolinguals on tasks based on interference suppression
and all the monolinguals and bilinguals performed
the same on tasks based on response inhibition. This
replication across the different participant groups
establishes the generalizability of the interpretation for a
bilingual advantage in one aspect of attentional control.
It also highlights the importance of being functionally
bilingual for cognitive effects to emerge.
In sum, the results of these three studies support the
conclusion that the development of attentional control
that is part of executive functioning and is used to
selectively attend to target cues in conflicting situations is
more advanced in bilingual children than in comparable
monolinguals. These results are consistent with previous
research but go beyond those earlier studies and contribute
to a more detailed understanding of the source of that
bilingual advantage. The advantage is not simply in
inhibition – tasks that required inhibition of a habitual
response were not solved better by bilinguals. Our explanation is that bilinguals must constantly control attention
between two active and competing language systems so
that communication can proceed fluently in the one that
is required. A large body of research has documented the
92
M. M. Martin-Rhee and E. Bialystok
conclusion that both languages are simultaneously active
when a bilingual is using one of them (e.g., Grainger and
Beauvillain, 1987; Brysbaert, 1998; Kroll and Dijkstra,
2002). The experience of controlling attention between
these two languages is a source of practice that boosts
those control processes and makes them available for
other tasks, such as the perceptual decision tasks used
in these experiments. In contrast, the Stroop naming
task does not replicate the bilingual experience; being
bilingual does not entail withholding or replacing habitual
responses. Therefore, the processes involved in response
inhibition that are required to process tasks based on
univalent stimuli are developed equally in monolingual
and bilingual children. This distinction between two types
of inhibitory control contributes to our understanding of
these crucial developing processes in young children and
the effect that a common experience, bilingualism, can
have on that development.
References
Arriaga, R. I., Fenson, L., Cronan, T. & Pethick, S. J. (1998).
Scores on the MacArthur Communicative Development
Inventory of children from low- and middle-income
families. Applied Psycholinguistics, 19, 209–223.
Bialystok, E. (1999). Cognitive complexity and attentional
control in the bilingual mind. Child Development, 70, 636–
644.
Bialystok, E. (2001). Bilingualism in development: Language,
literacy, and cognition. New York: Cambridge University
Press.
Bialystok, E. (2006). Effect of bilingualism and computer video
game experience on the Simon task. Canadian Journal of
Experimental Psychology, 60, 68–79.
Bialystok, E., Craik, F. I. M., Grady, C., Chau, W., Ishii, R.,
Gunji, A. & Pantev, C. (2005). Effect of bilingualism on
cognitive control in the Simon task: Evidence from MEG.
NeuroImage, 24, 40–49.
Bialystok, E., Craik, F. I. M., Klein, R. & Viswanathan,
M. (2004). Bilingualism, aging, and cognitive control:
Evidence from the Simon task. Psychology & Aging, 19,
290–303.
Bialystok, E., Craik, F. I. M. & Ryan, J. (2006). Executive
control in a modified anti-saccade task: Effects of aging
and bilingualism. Journal of Experimental Psychology:
Learning, Memory, and Cognition, 32, 1341–1354.
Bialystok, E. & Majumder, S. (1998). The relationship between
bilingualism and the development of cognitive processes in
problem solving. Applied Psycholinguistics, 19, 69–85.
Bialystok, E. & Martin, M. M. (2004). Attention and inhibition in
bilingual children: Evidence from the dimensional change
card sort task. Developmental Science, 7, 325–339.
Bialystok, E. & Senman, L. (2004). Executive processes in
appearance–reality tasks: The role of inhibition of attention
and symbolic representation. Child Development, 75, 562–
579.
Bialystok, E. & Shapero, D. (2005). Ambiguous benefits: The
effect of bilingualism on reversing ambiguous figures.
Developmental Science, 8, 595–604.
Brysbaert, M. (1998). Word recognition in bilinguals: Evidence
against the existence of two separate lexicons. Psychologica
Belgica, 38, 163–175.
Bunge, S. A., Dudukovic, N. M., Thomason, M. E., Vaidya,
C. J. & Gabrieli, J. D. E. (2002). Immature frontal lobe
contributions to cognitive control in children: Evidence
from fMRI. Neuron, 33, 301–311.
Corsi, P. M. (1972) Human memory and the medial temporal
region. Dissertation Abstracts International, 34(02),
891B.
Costa, A., Miozzo, M. & Caramazza, A. (1999). Lexical
selection in bilinguals: Do words in the bilingual’s two
lexicons compete for selection? Journal of Memory and
Language, 41, 365–397.
Daniels, K., Toth, J. & Jacoby, L. (2006). The aging of executive
functions. In E. Bialystok & F. I. M. Craik (eds.), Lifespan
cognition: Mechanisms of change, pp. 96–111. New York:
Oxford University Press.
Dempster, F. N. (1992). The rise and fall of the inhibitory
mechanism: Toward a unified theory of cognitive
development and aging. Developmental Review, 12, 45–
75.
Diamond, A. (2002). Normal development of prefrontal cortex
from birth to young adulthood: Cognitive functions,
anatomy, and biochemistry. In D. T. Stuss & R. T. Knight
(eds.), Principles of frontal lobe function, pp. 466–503.
Cambridge, MA: MIT Press.
Diamond, A., Kirkham, N. & Amso, D. (2002). Conditions under
which young children CAN hold two rules in mind and
inhibit a prepotent response. Developmental Psychology,
38, 352–362.
Diamond, A., O’Craven, K. M. & Savoy, R. L. (1998).
Dorsolateral prefrontal cortex contributions to working
memory and inhibition as revealed by fMRI. Society for
Neuroscience Abstracts, 24, 1251.
Diamond, A. & Taylor, C. (1996). Development of an aspect of
executive control: Development of the abilities to remember
what I said and to “do as I say, not as I do”. Developmental
Psychology, 29, 315–334.
Flavell, J. H., Flavell, E. R. & Green, F. L. (1983).
Development of the Appearance/Reality distinction.
Cognitive Psychology, 15, 95–120.
Flavell, J. H., Flavell, E. R. & Green, F. L. (1987). Young
children’s knowledge about apparent/real and pretend/
real distinctions. Developmental Psychology, 23, 816–
822.
Gerstadt, C. L., Hong, Y. J. & Diamond, A. (1994). The
relationship between cognition and action: Performance of
children 3;12–7 years old on a Stroop-like daynight test.
Cognition, 53, 129–153.
Gollan, T. H. & Kroll, J. F. (2001). Bilingual lexical access. In B.
Rapp (ed.), The handbook of cognitive neuropsychology:
What deficits reveal about the human mind, pp. 321–345.
Philadelphia, PA: Psychology Press.
Gollan, T. H. & Silverberg, N. B. (2001). Tip-of-the-tongue states
in Hebrew–English bilinguals. Bilingualism: Language
and Cognition, 4, 63–83.
Inhibitory control
Grainger, J. & Beauvillain, C. (1987). Language blocking
and lexical access in bilinguals. Quarterly Journal of
Experimental Psychology, 39A, 295–319.
Green, D. W. (1998). Mental control of the bilingual lexicosemantic system. Bilingualism: Language and Cognition,
1, 67–81.
Harnishfeger, K. K. & Bjorklund, D. F. (1993). The ontogeny of
inhibition mechanisms: A renewed approach to cognitive
development. In R. Pasnak & M. Howe (eds.), Emerging
themes in cognitive development (vol. 1), pp. 28–49. New
York: Springer Verlag.
Hommel, B. (1994). Spontaneous decay of response-code
activation. Psychological Research, 56, 261–268.
Kolb, B. & Wishaw, I. Q. (2001). An introduction to brain and
behaviour. New York: Worth Publishers.
Kroll, J. F. & Dijkstra, A. (T.) (2002). The bilingual lexicon. In
R. Kaplan (ed.), Handbook of applied linguistics, 301–321.
Oxford: Oxford University Press.
Kroll, J. F. & Stewart, E. (1994). Category interference in
translation and picture naming: Evidence for asymmetric
connections between bilingual memory representations.
Journal of Memory and Language, 33, 149–174.
La Heij, W. (2005). Selection processes in monolingual and
bilingual lexical access. In J. F. Kroll & A. M. B. de
Groot (eds.), Handbook of bilingualism: Psycholinguistic
approaches, pp. 289–307. New York: Oxford University
Press.
Lu, C.-H. & Proctor, R. W. (1995). The influence of irrelevant
location information on performance: A review of the
Simon and spatial Stroop effects. Psychonomic Bulletin
& Review, 2, 174–207.
Lu, C.-H. & Proctor, R. W. (2001). Influence of irrelevant
information on human performance: Effects of S–R
93
association strength and relative timing. Quarterly Journal
of Experimental Psychology A: Human Experimental
Psychology, 54A, 95–136.
Oller, D. K. & Eilers, R. (2002). Language and literacy in
bilingual children. Clevedon: Multilingual Matters.
Ozonoff, S. & Jensen, J. (1999). Specific executive function
profiles in three neurodevelopmental disorders. Journal of
Autism and Developmental Disorders, 29, 171–177.
Ozonoff, S., Pennington, B. F. & Rogers, S. J. (1991).
Executive function deficits in high-functioning autistic
individuals: Relationship to theory of mind. Journal of
Child Psychology and Psychiatry, 32, 1081, 1105.
Pascual-Leone, J. (1969). Water Level Test. York University,
Toronto.
Rescorla, L. (1989). The Language Development Survey: A
screening tool for delayed language in toddlers. Journal of
Speech and Hearing Disorders, 54, 587–599.
Simon, J. R. (1969). Reactions towards the source of
stimulation. Journal of Experimental Psychology, 81, 174–
176.
Simon, J. R. & Craft, J. L. (1970). Effects of an irrelevant
auditory stimulus on visual choice reaction time. Journal
of Experimental Psychology, 86, 272–274.
Tipper, S. P. (1992). Selections for actions: The role of inhibitory
mechanisms. Current Directions in Psychological Science,
1, 105–112.
Zelazo, P. D., Reznick, J. S. & Pinon, D. E. (1995). Response
control and the execution of verbal rules. Developmental
Psychology, 31, 508–517.
Received August 20, 2006
Revision received December 13, 2006
Accepted December 18, 2006
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