Assessing Selective Attention
in ADHD, Highly Creative,
and Normal Young Children
via Stroop Negative Priming Effects
Verena E. Pritchard, Dione Healey, and Ewald Neumann
Selective attention is conventionally taken to indicate the selection of one set
of sensory inputs over others. The selection of relevant over irrelevant stimuli is
fundamental for efficient interaction with the visual world. Such interaction relies
on selection mechanisms that allow for the direction of action to behaviourally
relevant items. Attention is influenced by both stimulus-driven (bottom-up) and
goal-directed (top-down) processes. According to one view of selective attention,
along with the enhancement of selected targeted information, there is a screening-
out or gating of unwanted, competing non-target stimuli (e.g., Cohen, Dunbar, &
McClelland, 1990; Desimone & Duncan, 1995). An alternative view regarding
such non-targets holds that they are not simply screened out, but implicitly regis-
tered and subjected to active inhibition (see Tipper, 2001, for a review). The
current study looks for evidence of active inhibition in groups of children with
potential differences relating to attentional processing.
Negative Priming and the Stroop Colour-Word Task
The active inhibition view can be traced to the seminal work of Dalrymple-
Alford and Budayr (1966) using Stroop stimuli. Stroop tasks typify a class of
interference effects whereby the introduction of task-irrelevant stimulus char-
acteristics slows reaction time. In Stroop interference tasks the naming of hues
is slowed by the presence of a word that consists of a task-irrelevant colour
name that differs from the ink colour of the task-relevant target stimulus. For
example, it takes longer to say ‘red’ to a red-coloured word when the word is
incongruent (e.g., green), than if it consists of a neutral stimulus comprising
random letters (e.g., iiiii).
While examining the effect of Stroop stimuli sequencing on interference,
Dalrymple-Alford and Budayr (1966) discovered an increased delay and greater
error rate for items appearing in the hue that had been the ignored word of the
previous Stroop stimulus. More specifically, response time was slower for a related
condition in which the colour specified by the colour-word in the preceding trial
matched the hue of the subsequent target than for an unrelated condition in
which the target hue was unrelated to the colour specified by the colour-word in
the preceding trial. This phenomenon is now called negative priming (Tipper,
1985) and refers to the finding that when a distracting, non-target stimulus is
ignored, a subsequent response to that stimulus (or a conceptually similar
stimulus) is typically slowed or less accurate, or both. Although negative priming
(NP) tasks have been used extensively to understand the nature of inhibitory
mechanisms underlying visual selective attention in adults, they have been under-
utilised in the assessment of these abilities in children. A primary goal of the
present chapter was to redress the neglect of this tool for investigating potential
inhibitory capacities in different populations of children. We thus employed a
Stroop negative priming task modeled on the early work of Dalrymple-Alford and
Budayr to measure attentional processing in three distinct populations of children:
30 diagnosed with attention-deficit/hyperactivity disorder (ADHD); 30 desig-
nated highly creative; and 30 matched controls.
The Active Inhibition Explanation of Negative Priming
In initial interpretations, the response cost associated with an ignored item was
attributed to the active suppression or inhibition of the ignored item’s representation
or to suppression of the access from that item to action (Tipper & Cranston, 1985).
This account of the NP phenomenon stems from activation–suppression models of
attention emphasising the operation of a dual mechanism during selection (e.g.,
Neill & Westberry, 1987; Neumann & DeSchepper, 1991; Tipper, 1985). According
to these models selection is postcategorical; initial analysis of both attended and
unattended stimuli takes place in parallel prior to selection. For a response to be
directed towards the target, an excitatory mechanism functions to enhance or
maintain the internal representation of the target, while an inhibitory mechanism
acts to suppress the competing distractor representation. From this perspective, inhi-
bition functions to enhance response to the target on a trial containing a specified
target and distractor by reducing potential interference from the distractor.
Inhibition-based theories of NP suggest that the NP effect may reflect inhi-
bition elicited as part of the selection process. Impaired or delayed response to
the target on the subsequent trial of an ignored repetition (IR) pair (whereby a
distractor becomes the subsequent target) in a NP task is attributed to inhibitory
processes associated with the distractor on the prior trial (Houghton & Tipper,
1994; Neumann & DeSchepper, 1992; Strayer & Grison, 1999). Such NP effects
are reliably demonstrated by young adults in a variety of NP tasks employing a
wide range of stimuli such as pictures, letters, words, novel shapes, structurally
possible and impossible three-dimensional shapes, and numbers (Driver & Tipper,
Cognition and Language
1989; Neumann, 1999; Tipper, 1985; Tipper & Cranston, 1985; Treisman &
DeSchepper, 1996). The observation of NP across such a wide range of stimuli
suggests that the associated inhibitory mechanism may be a general property of the
selection process in situations with intensively clashing target and concurrent
non-target information. It should be noted, however, that a competing explana-
tion for NP, known as episodic retrieval theory,denies any role for an inhibitory
selective attention mechanism (Neill, 1997; Neill & Mathis, 1998; Neill &
Valdes, 1992). Because findings from most recent studies suggest an inhibition-
based explanation remains the most influential account of NP (Buchner &
Steffans, 2001; Conway, 1999; Fuentes, Humphreys, Agis, Carmona, & Catena,
1998; Hughes & Jones, 2003; Khurana, 2000; Kramer & Strayer, 2001; Lavie &
Fox, 2000; Neumann, McCloskey, & Felio, 1999; Strayer & Grison, 1999; Wong,
2000), episodic retrieval theory will not be dealt with further. For a more detailed
discussion, however, see Pritchard and Neumann (2004).
Negative Priming and Attentional Deficits
Negative priming procedures are currently deemed the best available index for
investigating inhibitory processes in visual selective attention. Research exam-
ining NP effects in atypical adult populations has found that generalised cogni-
tive failures (Tipper & Baylis, 1987), certain brain pathologies such as
schizophrenia (Beech, Powell, McWilliam, & Claridge, 1989; Laplante, Everett,
& Thomas, 1992), aging (Hasher, Stoltzfus, Zacks, & Rypma, 1991; McDowd &
Oseas-Kreger, 1991; Tipper, 1991), and Alzheimer’s syndrome (Sullivan, Faust,
& Balota, 1995) are associated with a reduced or reversed NP effect. This
suggests that the efficiency of the distractor inhibition mechanism has direct
ramifications for attentional processing. Absent or reversed NP effects, for
instance, might imply a dysfunctional inhibitory processing mechanism, which
may in turn account for variability in cognitive performance.
Recent research investigating NP effects in varying age ranges of typical
children has shown that conceptual (i.e., identity or semantic) NP effects occur
in children as young as 5 years old (Pritchard & Neumann, 2004). These
findings contradict earlier work that suggested deficiencies in the inhibitory
mechanism of children (Tipper, Bourque, Anderson, & Brehaut, 1989). The
present study used a Stroop negative priming task to investigate and compare
potential differences in inhibitory processing in three distinct populations of
children (ADHD versus Highly Creative versus Control) between the ages of 10
and 12 years. Our primary objectives were (a) to assess whether conceptual NP
is a replicable phenomenon in children, (b) to investigate inhibitory processing
in children with recognised deficits in attentional processing in an attempt to
resolve discrepancies in the existing literature in this area, and (c) to investigate
the contribution of cognitive inhibition to the information processing style of
highly creative children. In the sections that follow, we provide a brief overview
of existing NP studies concerned with inhibitory function in children with
ADHD and creative individuals.
Assessing Selective Attention
Negative Priming Effects in Children With ADHD
ADHD has become one of the most common developmental disorders of child-
hood affecting 3% to 6% of children from varied cultures and geographical regions
(Hart, Leahy, Loeber, Applegate, & Frick, 1995). The core behavioural symptoms
of ADHD are inattention, impulsivity, and hyperactivity (American Psychiatric
Association, 2000). A deficit in behavioural inhibition (impulsiveness) is the
most distinguishing characteristic. This involves a failure to inhibit or delay a
behavioural response and is associated with a significant disruption in the ability
to control and regulate response and behaviour (Barkley, 1998; Tannock, 1998).
Many studies point to a dysfunction in inhibitory control as the cause for the
major deficits in children with attention deficit disorder (Barkley, 1997; Quay,
1988; Schachar & Logan 1990). Inhibitory control is classified as the ability of an
individual to delay a response, to interrupt an initiated response, to withhold a
planned response, and to protect an ongoing activity from interference (Rubia,
Oosterlann, Sergeant, Brandeis, & Leeuwen, 1998). Deficits in behavioural inhi-
bition and inhibitory control in ADHD may relate to a dysfunction associated
with the neurotransmission of dopamine (a neurotransmitter implicated in the
brain’s braking or inhibiting system) in the prefrontal cortex (Hynd et al., 1993).
The prefrontal cortex is assumed to modulate executive functions involved in
complex goal-directed behaviour and play a paramount role in the mediation of
various types of inhibitory function. Barkley (1994) assigns a central role to
inhibitory control in executive function, arguing that impairments in inhibitory
function in ADHD children may cause deficits typically shown by these children
across a range of executive tasks designed to tap or assess prefrontal function
(Barkley, Grodzinsky, & DuPaul, 1992; Pennington & Ozonoff, 1996; Ross,
Hommer, Breiger, Varley, & Radant, 1994). Effective performance on executive
function tasks often demands the ability to screen out, or in some way eliminate or
reduce, intrusion from task-irrelevant information via inhibition and attentional
control (Roberts & Pennington, 1996). A good example of this is the Stroop colour-
naming task where the salient feature is the prepotent–alternative response
dynamic. The prepotent tendency is to read the word while the alternative (correct)
response is to identify the colour of the ink. Children with ADHD typically demon-
strate heightened Stroop interference in comparison to typical children (see
Harnishfeger & Bjorklund, 1994, for a review). Researchers using the NP paradigm
to investigate central or cognitive inhibitory mechanisms in children with ADHD
have proposed that poor behavioural inhibition and inhibitory control, along with
increased susceptibility to interference in these individuals, may show up as a
reduced NP effect in comparison to NP effects in typical children.
Results from the few studies that have investigated NP effects in children with
ADHD are contradictory. Marriott (1998) used a letter-matching NP task to assess
possible deficits in underlying attention mechanisms in hyperactive and ADHD
children aged 10 to 12 years. Stimuli in this task consisted of a five-letter array
(e.g., TVTVT). The first, third, and fifth letters are always classified as distractors
and always identical to each other, while the second and fourth letters always
Cognition and Language
function as targets, and may differ from one another. On half of the trials, target
letters do not match (e.g., FTFXF), while on the remaining trials the target
letters are the same (e.g., FTFTF). The task requires participants to judge
whether the target letters are ‘same’ or ‘different’. Two conditions are compared;
unrelated (distractor and target letters are novel for consecutive trials) and IR
(one or both target letters appear as distractors on the immediately preceding
trial). Negative priming scores are calculated by taking the difference in reaction
time or error rate between the two conditions. Marriott (1998) found, that in
comparison to age-matched peers, hyperactive and ADHD children demon-
strated a significantly reduced NP effect on such a task. Diminished NP effects
have also been reported for 11- and 12-year-old children with Tourette
syndrome with comorbid ADHD on a letter NP task similar to that used by
Marriott, in comparison to age-matched children with Tourette syndrome but
without ADHD comorbidity and typical children (Ozonoff, Strayer, McMahon,
& Filloux, 1998). According to Ozonoff et al., these findings suggested that the
presence of ADHD in individuals with Tourette syndrome impairs performance
on select variables indicative of a specific inhibitory deficit.
In contrast, a study by Gaultney, Kipp, Weinstein, and McNeill (1999)
employing a Stroop NP task found significant NP effects for both ADHD and
typical children matched in age (9 to 12 years) and IQ. Participants in their
study were all required to complete two identical versions of the Stroop NP task.
Because Gaultney et al. were also interested in assessing the effects of stimulant
medication on NP effects, children with ADHD were required to complete
double administrations of the Stroop NP tasks: one session while medicated and
one session while unmedicated. These sessions were counterbalanced. Typical
children in their study were only required to complete one session. Gaultney and
colleagues predicted that because ADHD is associated with deficits in behav-
ioural inhibition and inhibitory control, a deficit in cognitive inhibition may
also be implicated. Thus, children with ADHD may present with a diminished
NP effect. An additional prediction made by these authors was that NP effects
for ADHD participants would increase when these individuals were medicated.
Neither hypothesis was supported. Negative priming effects were invariant
across the two versions and both sessions of the Stroop NP task for the ADHD
participants. More importantly, while children with ADHD demonstrated a sig-
nificant increase in response latency on both unrelated and IR priming condi-
tions on the second version of the two Stroop NP tasks relative to typical
children in the first session, the critical NP effect was significant and invariant
across the two groups on both the first and second versions of the task.
Contradictions in the literature concerning the relationship between
ADHD and NP effects do not allow for any clear-cut conclusions to be drawn
regarding the ability of these children to inhibit distracting information. Rather
they beg the question — are the inhibitory mechanisms underlying visual selec-
tive attention dysfunctional in children diagnosed with ADHD?
Assessing Selective Attention
Negative Priming Effects in Creative Individuals
There has been some speculation that enhanced creativity may be associated
with reduced cognitive inhibition (Green & Williams, 1999; Stavridou &
Furnham, 1996). By definition, creativity is demonstrated by some sort of novel
outcome, whether it be a solution to a problem, a completed communicable
idea, or something tangible like a work of art or an invention (Akande, 1997;
Bogen & Bogen, 1999; DuBrin, 1994; Parkhurst, 1999; Pearlman, 1983; Piirto,
1998). One prominent thought process involved in creativity is divergent
thinking; the production of a large number of original and unexpected ideas to
form solutions for a given problem.
Stavridou and Furnham (1996) proposed that divergent thinking may relate
to a weakness in cognitive inhibition. This conjecture was loosely based on
research concerning reduced NP effects in individuals diagnosed with schizo-
phrenia. Stavridou and Furnham argued that a deficit in inhibitory selective
attention mechanisms may make individuals with schizophrenia unable to
inhibit irrelevant information and prevent it from entering consciousness.
Consequently, many unrelated ideas become interconnected resulting in
‘widened associative connections’. This then results in more unusual associa-
tions between words and ideas compared with typical individuals. Stavridou and
Furnham go on to suggest that the ‘wide associative horizons’ that typically char-
acterise individuals with schizophrenia are similar to the thought processes that
define creativity; that is, attention to multiple variables of a given stimulus and
the subsequent production of more varied associations. In accordance with this
logic, they predicted that because individuals with schizophrenia present with
reduced NP effects, individuals who score highly on measures of divergent
thinking may also exhibit diminished NP effects. Results from their NP Stroop
task failed to support this hypothesis. Significant and similar NP effects were
obtained for both high and low divergent thinking scorers. However, Stavridou
and Furnham did note that, although not statistically significant, participants
who scored highly on divergent thinking measures did present with a smaller NP
effect in comparison to low scorers. Green and Williams (1999) suggested that
Stavridou and Furnham’s failure to find any significant association between NP
and divergent thinking scores may relate to the small sample size that was used,
or to modifications that were made to the timing of stimulus presentation within
the priming procedure used in the study. Green and Williams (1999) employed
a larger sample size and used a modified version of Stavridou and Furnham’s
(1996) Stroop NP task. Again, the prediction was that high scores in divergent
thinking tasks would associate with a reduced NP effect in comparison to low
scores. This was not supported. In fact, results from Green and Williams’s study
were characterised by an overall absence of NP effects across all participants.
Green and Williams (1999) acknowledge that their failure to achieve NP effects
may relate to problems with the experimental design they employed, such as the
non-randomisation of priming conditions across trials. Green and Williams’s
Stroop NP task consisted of three experimental conditions; neutral, unrelated,
Cognition and Language
and IR. The presentation order for all participants was always IR trials followed
by unrelated trials followed by neutral trials. Because IR trials were never inter-
spersed with unrelated or neutral trials, participants may have noticed the rela-
tionship between prime distractor and probe target stimuli in this condition
(i.e., the distractor colour word on the prime trial names the probe trial target
colour). It is well documented that when participants become aware of the NP
manipulation, they can potentially use this information to predict test targets on
ignored repetition probe trials (Hasher et al., 1991; Neumann & DeSchepper,
1991; Stoltzfus, Hasher, Zacks, Ulivi, & Goldstein, 1993). This may result in a
decreases rather than increases in response latency on IR trials, relative to unre-
lated trials where prime distractor and probe target are never related (see May,
Kane, & Hasher, 1995, for a review). Clearly, the evidence for compromised
inhibition in creative individuals is equivocal. Research by Stavridou and
Furnham (1996) points to the faint possibility of a link between reduced NP
effects and divergent thinking. Attempts to follow up this study have been
unsuccessful, marred by potential methodological problems (Green & Williams,
1998). There is no conclusive evidence to suggest that divergent thinking,
possibly a dominant feature of the creative process, is associated with a deficit in
In the present experiment, children ranging in age between 10 and 12 years
old were tested to see if they would produce NP in the present Stroop NP task.
In addition, children with ADHD were specifically tested to determine if they
would show evidence for a diminished NP effect, in comparison to control
children. Lastly, the performance of highly creative children was assessed in
order to determine if they would produce a reduced NP effect relative to controls
in light of recent speculations that creativity may be associated with weakened
cognitive inhibition. Because of the variety of discrepancies in the literature, the
present results should enable either verification or disconfirmation of the studies
covered in our review.
Ninety children aged between 10 and 12 years participated in the experiment. The
children were divided into three groups: 30 (23 male, 7 female) were diagnosed
with ADHD, 30 (14 male, 16 female) were identified as highly creative, and 30
(13 male, 17 female) were classified as controls with normal creativity scores and
no indication of ADHD. Hereafter, these will be referred to as the ADHD,
Creative, and Control groups, respectively. The mean age for the respective groups
was 11 years 2 months (SD = 0.82), 11 years 5 months (SD = 0.85), and 11 years
10 months (SD = 0.89). Recruitment was conducted through advertisements in
local newspapers, school notices, an ADD support group newsletter, and a
Gifted Children’s Society newsletter. The ADHD group was established by con-
firming that each child was diagnosed with ADHD by a psychiatrist or registered
psychologist. Participants in the ADHD group were unmedicated on the day of
Assessing Selective Attention
testing. Participants in the ADHD group who were receiving psychostimulant
(dextroamphetamine or methylphenidate) medication discontinued their treat-
ment 24 hours before the day of testing because of the known effects of
methylphenidate on cognitive functioning (e.g., Berman, Douglas, & Barr,
1999). As methylphenidate has an approximate half-life of 4.5 hours (Shader,
Harmatz, Oesterheld, Parmelee, Sallee, & Greenblatt, 1999), a 24-hour elimi-
nation period should have ensured that the majority of the active ingredient had
been eliminated prior to testing. The Creative group was established by con-
firming that each child scored in the 92nd percentile, or higher, on the Torrance
Test of Creative Thinking (TTCT; Torrance, 1962). Participation was voluntary
and included parental consent and child assent. All children had normal colour
vision and normal or corrected to normal visual acuity. Participants were pre-
dominantly Caucasian of varying socioeconomic score (SES) backgrounds
residing in Christchurch, New Zealand.
The study employed a mixed design. The between-subjects variable was group
(ADHD versus Creative versus Control) and the within-subjects variable was
priming condition (Unrelated versus IR). Half the trials in the experiment were
Unrelated (UR) trials (where neither the hue nor distractor colour word in a
display were repeated in the subsequent display) and half IR trials (where the
distractor word in a previous display repeated as the subsequent target hue). See
Figure 1 for a sample of these conditions.
Apparatus and Stimuli
The stimuli were presented on 26 cm ×18 cm laminated cards and consisted of
the words BLUE, RED, PURPLE, PINK, ORANGE, YELLOW, BROWN,
GREEN, WHITE, GREY, and BLACK. These were all printed as a vertical list
and displayed against a light grey background on each UR and IR card. Lettering
measured 1.0 cm in height with each word spaced at 1.0 cm intervals down the
list. The 11 Stroop items in each card were arranged in a single vertical column
with the print of each word presented in one of the 11 corresponding colours.
The first two items on each IR card were unrelated in order to reduce the
saliency of this condition (see Figure 1). Test cards consisted of six IR cards and
six UR cards. Four additional UR cards were used for practice trials. Each word
and each ink colour appeared only once on a given card.1Presentation orders in
the experiment were counterbalanced so that half of the participants began with
a UR card and the remaining half began with an IR card. Subsequent cards were
presented in regular alternation of the two conditions. A stopwatch was used to
measure response latencies to complete the colour naming for each card.
In a double-blind experiment, participants were tested individually in a quiet
room. Prior to the experiment, participants completed a colour vision task
requiring identification of the 11 ink colours used in the experiment. The colours
Cognition and Language
were presented in a vertical column of small squares on a 26 cm ×18 cm laminated
card. This was done both as a test of colour vision and to ensure familiarity with
the entire set of colour names used in the experiment. Participants were then
verbally instructed to name as quickly and accurately as possible the colour of the
ink that each word was printed in from the top to the bottom of the column on a
card. They were asked not to stop if an error was made but to continue until the
colour naming for the card was completed. Each participant encountered four UR
practice cards before the commencement of test cards for the experiment. In the
experiment proper, participants were given the 12 test cards (six per condition pre-
sented in alteration). For each card the experimenter said ‘Ready’ as a warning and
on the word ‘Go’ a blank card covering the test card was removed and the stop-
watch started. The stopwatch was stopped in synchrony with the naming of the
last colour on a card. Error scores for each card were recorded and classified as
either omissions or verbalisations of an incorrect colour.
For each participant a mean response time per item (RT) was computed for the
six cards representing the UR condition and the six cards representing the IR
condition. Mean RTs and percentage of errors for the UR and IR conditions are
shown for the three groups in Table 1.
A two-way mixed analysis of variance (ANOVA) was carried out on the mean
RTs. The between-subjects variable was group (ADHD versus Creative versus
Control) and the within-subjects variable was priming condition (UR versus IR).
Assessing Selective Attention
Unrelated Ignored Repetition
Example of unrelated and ignored repetition trials.
Note: Children were asked to name the ink colour of the Stroop item in each column as quickly and accurately as possible from the
top to the bottom of each card.
The between-subjects variable of group was significant, F(2, 87) = 10.57, p< .001.
In order to determine whether there were differences in the overall RTs
between the groups, Newman-Keuls post hoc analyses were conducted. The
results indicated that the ADHD group responded significantly more slowly
than both the Creative and Control groups, (ps < .001), but there was no dif-
ference between the Creative and the Control groups. More critically, the
within-subjects variable of priming condition (UR versus IR) was significant,
F(1, 87) = 6.74, p< .02, and there was no hint of an interaction, F< 1.
Participants responded slower on the IR trials than on the UR trials. The NP
effect was thus similar across the three groups and was unrelated to overall pro-
cessing speed. Additional support for the statistical outcome was evidenced in
the percentage of participants showing NP effects in each group; 60% (ADHD),
63% (Creative), and 63 % (Control).
Similar analyses were conducted for error scores. The between-subjects
variable of group (ADHD versus Creative versus Control) was significant, F(2,
87) = 8.06, p< .001. Newman-Keuls analyses indicated that the ADHD group
made significantly more errors than the other two groups (ps < .01). No other
error effects were significant. Because each of the three groups produced numer-
ically more errors in the IR than the UR condition, there is no indication of
speed-accuracy trade-offs that could compromise the RT analyses.
The specific purpose of this study was to examine potential differences in NP
effects between three distinct populations of children. With regard to earlier
empirical discrepancies and ambiguities in studies with typical, ADHD, and
highly creative children, results from our Stroop NP task revealed conceptual
NP to be both significant and invariant between these groups. Children with
ADHD, however, do appear to encounter significantly more Stroop interference
than either creative or control children, as evidenced by their longer RTs in both
UR and IR conditions. These findings make direct contributions to the existing
literature on NP effects in children and may also have important implications
for research concerned with ADHD. Contrary to the findings from previous
Cognition and Language
Mean Reaction Time in Milliseconds per Item and Percentage of Errors for Each Group Type
as a Function of Priming Condition
ADHD Highly Creative Control
UR IR UR IR UR IR
M1436 1500 1122 1175 1089 1125
SD 423 410 315 354 286 255
ER (%) 5.9 6.9 3.2 4.1 3.5 3.7
studies by Marriott (1998) and Ozonoff et al. (1998) that failed to obtain signif-
icant NP effects in children with ADHD, results from our study showed that
cognitive inhibitory capacity is intact in these individuals. Our results provide
further empirical support for the similar findings reported by Gaultney et al.
(1999). Taken together, the outcome of these later studies afford an opportunity
to discuss potential sources of inhibitory processing in NP tasks, in contrast with
other tasks commonly employed in testing children with ADHD. Much of the
contemporary research literature on ADHD points to a widespread deficit in
inhibitory function in individuals with ADHD. In accordance with this litera-
ture, researchers using the negative priming paradigm to investigate cognitive
inhibition in children with ADHD have predicted, not unreasonably, that a
deficit in cognitive inhibition may also underlie the symptoms of ADHD.
Therefore, children with ADHD should present with a reduced NP effect. This
is questionable on the basis of findings by Gaultney et al. (1999) and the current
study, however. Instead, these studies seem to imply that NP may reflect a
specific type of cognitive inhibition, one that may operate independently of
other inhibitory processes deemed to play a pivotal role in prefrontal function.
Two typical tasks that have been used to assess inhibitory function in ADHD
children are the go/no-go task and the stop-signal task. The go/no-go task taps
behavioural inhibition, requiring either the execution or the inhibition of a
response to a stimulus in a series of sequential trials depending on whether the
stimulus has been previously specified as a ‘go stimulus’ or a ‘no-go stimulus’. The
stop signal task tends to rely on inhibitory control. Participants need to inhibit
or interrupt a planned, but not yet initiated, response to the target stimulus pre-
sented on screen when a stop signal, either auditory or visual, is presented
directly after the onset of the target stimulus. Hyperactive and ADHD children
demonstrate impairments on both of these tasks, usually presenting with an
increased rate of errors in comparison to typical children (Rubia et al., 1998;
Vaidya et al., 1998). From our perspective, the type of inhibition that is impli-
cated in the go/no-go task and the stop signal task are unlikely to relate to the
distractor inhibition that may underlie NP effects. While children with ADHD
demonstrate inhibitory impairment in the go/no-go and the stop signal tasks,
they do not present with any evidence to suggest impairment in inhibitory
processes underlying NP. There is also empirical evidence with adults to suggest
that go/no-go tasks and NP tasks measure distinct types of inhibition. A study
by Kramer, Humphery, Larish, Logan, and Strayer (1994), for example, found no
correlation between NP effects and performance on the go/no-go task.
Although we found NP effects for ADHD children to be equivalent to those
of highly creative and control children, the response latency for both UR and IR
conditions of our Stroop NP task was significantly greater for ADHD children
in comparison to the other two groups. Note that similar trends were found by
Gaultney et al. (1999) for UR and IR priming conditions on both versions of
their Stroop NP task for ADHD children relative to typical children. This dif-
ference between the groups reached statistical significance for the second
Assessing Selective Attention
version of their Stroop NP task. There is some debate as to whether the noted
increase in response latency on the Stroop test for ADHD children relates to
heightened susceptibility to distractor intrusion (see Harnishfeger & Bjorklund,
1994; Pennington & Ozonoff, 1996; Rucklidge & Tannock, 2002, for reviews).
Given that we found intact NP effects for this group, the above conjecture loses
some credibility, at least in the Stroop NP paradigm. Rucklidge and Tannock
(2002) suggested that increased naming latencies for ADHD individuals may
relate to an overall slowness in information processing and name retrieval rather
than to interference effects associated with distractor intrusion. When compar-
ing interference effects on the Stroop Colour and Word Naming test between
adolescents with ADHD and age-matched controls, Rucklidge and Tannock
found that in comparison to controls, while those with ADHD were slower to
name colour words, colours, and incongruent colour-words, there were no group
differences in interference scores. A more recent study by Pritchard, Neumann,
and Rucklidge (in press) lends further empirical support to conjectures arising
from findings in the current study and those by Rucklidge and Tannock (2002)
regarding issues of Stroop interference and NP levels in ADHD individuals.
Pritchard et al. (in press) used a similar technique to Rucklidge and Tannock to
compare Stroop interference levels in addition to comparisons of NP effects
between typical adolescents and those with ADHD. It was found that, while the
ADHD group was consistently slower to name target stimuli in comparison to
the typical group, there were no differences in interference or NP between the
two groups. Increased response latencies in both conditions of the Stroop NP
task in children with ADHD imply a possible maturational lag in some aspects
of information processing. That is, the performance of 10- to 12-year-old
children with ADHD on the Stroop negative priming task mirrors the perform-
ance of five to six year old children on the same task. A developmental study by
Pritchard and Neumann (2004), found that while 5- and 6-year-old children
produce similar magnitudes of NP to children between the ages of 8 and 12
years, overall response latencies for the younger children were significantly
greater compared to those for the older children. Further research is clearly
required to establish the nature of this maturational lag for children with
ADHD, if indeed such a lag exists.
Our final goal was to test hypotheses concerning possible associations
between creativity and cognitive inhibitory function. Recall that Stavridou and
Furnham (1996) and Green and Williams (1999) suggested that compared with
typical individuals, creative individuals may demonstrate a reduced NP effect.
Results from our study failed to support this prediction, at least with children.
Instead, our results imply that the inhibitory process implicated in the NP effect
appears to be invariant across typical and creative children. Thus, the creative
thought processes implicated in divergent thinking do not necessarily appear to
be associated with a deficit in cognitive inhibitory capacity.
Cognition and Language
Toward Resolving Discrepancies
The specific reasons for the discrepancies between the results of the present
experiment and others regarding NP effects with typical children and in
children with ADHD are unclear. It is worth noting, however, that the contra-
dictory results with atypical children emulate previous contradictions in NP
studies with older adults, typical children, and Alzheimer’s disease where early
reports of inhibitory impairment are being supplanted by studies revealing intact
and comparable NP effects in these individuals. A clear example of this trend is
evident in the early developmental NP literature. While Tipper et al. (1989)
failed to find significant NP effects for children between the ages of 7 and 8
years, Pritchard and Neumann (2004) found significant levels of NP in children
as young as 5 years. A similar pattern exists in investigations of NP effects in
older adults and patients with Alzheimer’s (cf. Langley, Overmier, Knopman, &
Prod’Homme, 1998; Sullivan et al., 1995; see also Gamboz, Russo, & Fox 2002).
The specific reasons for discrepancies between the earlier and more recent
studies in these domains remain unresolved.
Given the discrepancies that exist in the ADHD NP literature regarding the
prevalence of this effect, however, it is suggested that NP effects in ADHD pop-
ulations, like those in typical developmental populations, may be sensitive to
variations in task design (see Pritchard & Neumann, 2004). Moreover, the typ-
ically small size of the NP effect coupled with a propensity for increased vari-
ability in ADHD individuals, or the use of too small sample sizes, might help
explain the lack of NP in some of these studies. Buchner and Mayr (2004)
provide a particularly cogent discussion on how these issues apply more gener-
ally to atypical populations engaged in NP tasks. What seems clear, however, is
that generally impaired performance in attentional tasks is not necessarily asso-
ciated with a deficit relating to the inhibition of irrelevant information during
selection. Thus, impaired performance across a range of attentional tasks that
require various sources of inhibition and resistance to distractor intrusion does
not necessarily lead to decreased NP effects.
Cognitive Inhibition: A Rudimentary Information Processing Mechanism?
The negative priming paradigm offers a unique opportunity to investigate dedi-
cated inhibitory mechanisms involved in the selection of relevant over irrele-
vant information. Findings from the current study support the contention that
the inhibitory mechanism underpinning conceptual NP effects may be a basic or
primitive processing resource (Neumann & DeSchepper, 1991, 1992). If so,
negative priming effects may reflect a fundamental information processing
mechanism inherent across a wide range of distinct populations and largely
distinct from other processes implicated in reduced or enhanced cognitive per-
formance. The failure to find any significant variability between the NP effects
for three distinct populations of children supports the view that NP effects
reflect the workings of a primitive and fundamental information processing
mechanism which develops at an early age and is unlikely to become defective
Assessing Selective Attention
even in persons with known attentional deficits. Here the specific cognitive
inhibitory mechanism implicated in NP does not appear to contribute to, or
mediate, individual differences in cognitive performance. This is not to say that
other specific inhibitory functions may not show declines in various populations.
On a more theoretical note, if nontarget information in strong conflict with
concurrent target information undergoes active inhibition, and the resulting
suppression of irrelevant (or unwanted) items produces NP effects, then cogni-
tive psychology’s most influential general models of selective attention
(Desimone & Duncan, 1995) and more particularly Stroop interference resolu-
tion (Cohen et al., 1990) should be questioned. Since these theories do not
contain this type of inhibition-based processing in their frameworks, it is
possible they are missing one of the key information processing mechanisms in
the human repertoire (cf. Cohen, Dunbar, Barch, & Braver, 1997; Schooler,
Neumann, Caplan, & Roberts, 1997a, 1997b).
1 This did not hold for IR cards as the inclusion of one unrelated prime-probe couplet at the
beginning of each IR card meant that one ink colour had to appear twice as a target to the
exclusion of another. Consequently, whereas each control card had 11 different target
colours to be named, an IR card had only 10 with one reappearing to be named for a second
time so that the total number of target colours to be named was the same for both the
control and IR cards. A supplementary control experiment using Stroop stimuli was con-
ducted to determine whether any detrimental artefact could have emerged from presenting
a duplicate colour only in the IR condition. Two conditions were assessed. Naming 11
unique colours once versus naming nine unique colours and one duplicate colour. The
results from that experiment ruled out the possibility that including one duplicated target
colour could yield a delay compared to cards with no duplicated target colours. Thus, it is
unlikely that the interpretation of IR NP effects in the present experiment would be com-
promised by this potential artefact.
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