2013. Vol.4, No.10A, 29-33
Published Online October 2013 in SciRes (http://www.scirp.org/journal/psych) http://dx.doi.org/10.4236/psych.2013.410A006
Copyright © 2013 SciRes. 29
The Effects of Hand Preference on Attention
Sergio L. Schmidt1, Eunice do Nascimento Simões1, Guilherme J. Schmidt2,
Ana Lucia Novais Carvalho3
1State University of Rio de Janeiro, Rio de Janeiro, Brazil
2Institute of Neurology Deolindo Couto, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
3Fluminense Federal University, Niteroi, Brazil
Received August 3rd, 2013; revised September 5th, 2013; accepted September 26th, 2013
Copyright © 2013 Sergio L. Schmidt et al. This is an open access article distributed under the Creative Com-
mons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, pro-
vided the original work is properly cited.
Handedness is associated with cerebral hemispheric differences. Normal patterns of brain asymmetries are
needed for the neural processing of attention. In order to identify ADHD (Attention Deficit Hyperactive
Disorder) children, the use of checklists allows a greater level of accuracy. Here, we will review our data
on this subject. Our first study investigated the psychometric properties of a scale developed to assess at-
tention disorders. Our second study investigated the relationship between handedness and attention disor-
ders using the factors derived from the scale. Our third study included the use of a continuous visual test
of attention (CVAT) and examined the relationship between handedness and CVAT variables. For the
first and second study, 239 students were included. From this sample, 42 students were selected to parti-
cipate in the third study. Forty-five teachers rated the children. Four factors were extracted: hyperactiv-
ity/impulsivity (explained variance = 36.3%); inattention (11.4%); social isolation (5.2%) and self-confi-
dence (explained variance = 3.3%). Sixty-eight children were included in the ADHD group. We found a
higher number of consistent left-handers in the ADHD group as compared to the normal group and a sig-
nificant effect of handedness on factor hyperactivity/impulsivity. This indicated that left-handers showed
greater problems in the hyperactivity-impulsivity domain as compared to right-handers. Considering the
data derived from CVAT, a significant handedness effect was found only for the variable commission er-
rors. Left-handers with attention problems showed the greatest number of errors and normal dextrals the
lowest number of errors. Normal left-handers made significantly more errors than normal dextrals. Com-
mission error is a parameter that is commonly viewed as a measure of impulsivity. Our data show that
hyperactivity/impulsivity is related to handedness, because left-handers present more problems in impul-
sive behavior than right-handers and suggest that consistent left-handed subjects show greater probability
to develop ADHD as compared to right-handed subjects.
Keywords: ADHD; Handedness; Laterality
The presence of primary disorder of inattention and/or hy-
peractivity/impulsivity is a diagnostic criterion for Attention
Deficit Hyperactive Disorder (ADHD), which is the most
common childhood psychiatric disorder, affecting 5% of the
school population. According to the Diagnostic and Statistical
Manual of Mental Disorders-5th Edition (2013), these behav-
ioral changes must be present in more than one venue fre-
quented by children, and their behavior at home and at school
are commonly rated through by parents and teacher. As sug-
gested by Mares, McLuckie, Schwartz & Saini (2007) and Tripp,
Schaughency & Clarke (2006), it is essential to collect data from
these two sources, considering that parents and teachers em-
phasize different aspects during the evaluation. Such differ-
ences are commonly described in the literature (for example:
Mitsis, McKay, Shultz, Newcorn, & Halperin, 2000). Cho et al.
(2011), in a recent study that aimed to compare data obtained
from scale for teachers and parents in the assessment of cogni-
tive performance in children, confirmed these data. These authors
find that teachers are more skilled in assessing hyperactive/
impulsive behavior, which facilitates the identification of chil-
dren with low cognitive performance. Such a facility by profes-
sionals is probably related to the fact that teachers know about
child development and deal with a large number of children.
This finding does not exclude the need for data collection
though filling out scales by parents. The study makes clear that
parents and teachers point out different but important aspects
on child behavior.
Previous studies have shown that psychologists who rely
only on their clinical judgment may experience difficulties in
identifying children with behavioral problems (Barkely, 1990;
Schmidt, Snyder, Rouget, & Gray, 2000). The use of checklists
completed by teachers or parents allows a greater level of ac-
curacy, even when considering the limitations of the instru-
ments (Greenhill, 1998; Schatz, Ballantyne & Trauner, 2001;
Ulloa, Narváez, Arroyo, del Bosque, & de la Peña, 2009). Stud-
ies have demonstrated that, in some cases, behavior rating
scales are even more effective in classifying children with
learning and cognitive disorders than traditional psychological
S. L. SCHMIDT ET AL.
tests (Dewey, Crawford, & Kaplan, 2003). The results demon-
strated that the scale was more efficiently in classifying chil-
dren with ADHD than the psychometric measures alone. Still
on the use of scales, an American research with 401 pediatri-
cians and family practice physicians, in a prospective cohort
study of 22.059 children from 4 to 14 years, showed that 53.5%
of them used school reports to diagnose attentional or hyperac-
tivity problems (Carey, 1999).
Our first study describes a scale developed by us to assess
hyperactive/impulsive behavior and inattention to be filled by
teachers. This study was performed to provide information
about the psychometric properties of this scale, including the
analysis of its reliability and validity, which was essential char-
acteristics of an instrument that is to be used clinically (Glascoe,
Martin, & Humphrey, 1990; Meisels, 1989).
Our second study will provide some information about
handedness which is an important issue that psychologists must
take into account in their assessments. Language lateralization
is associated with handedness in children. In fact, there is an
atypical language lateralization in left-handed children similar
to that reported in adults (Szaflarski et al., 2012). The finding
that handedness may be associated with structural and func-
tional differences has led many researchers to study a possible
relationship between handedness and neuropsychiatric diseases.
Several studies have demonstrated that among children with
learning disabilities, such as dyslexia, autism, and develop-
mental coordination disorder, left-handedness is more common
than in the general population (Cairney et al., 2008; Eglinton &
Annett, 1994; Goez & Zelnik, 2008). Abnormal brain connec-
tivity has recently been reported in Obsessive Compulsive Dis-
order (Di Paola et al., 2012). Regarding ADHD, the conclu-
sions are not clear. Rodriguez and Waldenström (2008) studied
the possible relationship between handedness and mental health
in a sample of 1714 children. They found a higher than ex-
pected proportion of left-handedness in children with impulsive
and/or hyperactivity behavior. Although Rodriguez and Wal-
denström (2008) reported handedness in a large sample, its
assessment was done by means of a questionnaire answered by
the mothers. Several studies (Mitsis, Mckay, Schulz, Newcorn,
& Halperin, 2000; Schmidt, Snyder, Roget, & Gray, 2000) have
shown that data derived from parents’ reports must be inter-
preted with caution. In contrast, Reid and Norvilitis (2000)
directly observed the hand used by the children, a procedure
known to be much more reliable than parents’ report. They
concluded that ADHD was not exclusively related to the preva-
lence of non-right-handedness. However, the sample size was
too small, especially regarding the expected number of left-
handers. More recently, Rodriguez et al. (2010) demonstrated
that mixed-handedness was associated to increased risk for lan-
guage difficulties and ADHD in late adolescence. From the
above mentioned studies, we concluded that the relationship
between handedness and attention disorder was still controver-
sial. Therefore, we investigated this controversial relationship
using direct observation of handedness.
Our third study included the use of a continuous performance
test (CPT) developed by one of us. The CPTs are usually used
to objectively assess attention (DuPaul, Anastopaulos, Shelton,
Guevremont, & Metevia, 1992). Rosvold et al. (1956) demon-
strated that CPTs were highly sensitive to brain damage or dys-
function. In particular, the CPTs have been shown to differenti-
ate ADHD from normal groups (Epstein et al., 2003). Several
variables may be derived from the CPTs, including errors of
omission and commission, mean hit reaction time (RT), mean
hit RT standard error, and signal detection measures (Epstein et
al., 2003). The interpretation of each CPT parameter (Conners,
Epstein, Angold, & Klaric, 2003; Riccio, Cohen, Hynd, &
Keith, 1996; Tinius, 2003) has largely been based upon clinical
assumptions and the face validity of each measure (e.g. omis-
sion errors measure inattention, commission errors measure
impulsivity). In general, the parameters can be divided into
three types: inhibition of response, inattention to stimuli, and
stability of processing time (Epstein et al., 2003; Riccio et al.,
2002). Functional neuroimaging studies are consistent with
models of sustained attention that involve the interaction of
cortical (frontal, temporal, parietal) and subcortical (limbic,
basal ganglia) structures (Riccio et al., 2002). An extensive
neural network is activated during the execution of the task that
includes the frontal, cingulate, parietal, temporal, and occipital
cortices; the cerebellum and the basal ganglia (Honey et al.,
2005). Moreover, significant differences between the left and
the right hemisphere have also been reported (Riccio et al.,
2002). In particular, ventral frontal region and parietal lobe
activation were greater in the right hemisphere (Honey et al.,
2005). Asymmetry favoring the activation of the right hemi-
sphere is reported by many researches (Riccio et al., 2002).
These studies support the view that execution of the CPT is
associated with cerebral asymmetric activation. Therefore, our
third study attempted to examine a possible relationship be-
tween handedness and CPT variables in normal and ADHD
children. We should mention that handedness will be measured
by direct observation and attention problems will be assessed
by a valid teacher scale for attention disorders (Carvalho, Man-
hães, & Schmidt, 2012).
A total of 239 students participated in the first and the second
study (validity of a teacher scale and relationship between
handedness and factors derived from the scale, respectively).
The sample consisted of 120 boys (mean age = 9.17 years, SD
= 2.51 years, minimum = 5 years, maximum = 18 years) and
119 girls (mean age = 9.11 years, SD = 2.76 years, minimum =
6 years, maximum = 17 years), from elementary schools.
From this sample, a total of 42 students were selected to par-
ticipate in the third study. The sample consisted of 25 boys
(mean age = 10.88 years, SD = 4.08 years, minimum = 5 years,
maximum = 18 years) and 17 girls (mean age = 10.31 years, SD
= 3.68 years, minimum = 6 years, maximum = 15 years). There
was no difference regarding male and female age (t = −0.44; df
= 40; p > 0.40). The selection was designed to pair handedness
matched by age, gender, and behavioral observations.
Forty-five teachers rated the children. The teacher selected to
rate a particular child was the one that spent most of the time
with the child.
The child’s participation in the research was voluntary. Par-
ents and school principals signed informed consents regarding
the voluntary participation of the children in the research. The
participation of the teachers was also voluntary. These studies
were approved by all local Ethics Committees.
The scale is composed of 58 questions with information
about behavior in the classroom, peer group, and disruptive
Copyright © 2013 SciRes.
S. L. SCHMIDT ET AL.
behavior. These questions are rated on an oral assessment scale
ranging from 1 to 3 reflecting problem prevalence (1 = not true;
2 = somewhat or sometimes true; 3 = very true or often true).
The internal consistency of the 58 scorable items scale was
evaluated using Cronbach’s alpha. Alpha is a correlation coef-
ficient and ranges in value from −1 to 1. If Cronbach’s alpha
drops below 0.7, the hypothesis of internal reliability cannot be
accepted (Barret & Kline, 1981; Cattell, 1966). To evaluate
how each individual item affects the reliability of the scale,
alpha was calculated removing each of the items of the scale.
Raw data from the questionnaire were factor analyzed. To
find the simplest possible factor structure, an orthogonal vari-
max rotation that maximizes the variance of the squared load-
ings for each factor was used. Only factors that account for
variances greater than 1 (eigenvalue greater than 1) were in-
cluded. With regard to the factor loadings, we considered only
the most highly correlated variables (greater than 0.50) for each
Evaluation of Hand Preference
Hand preference was assessed by direct observation of three
tasks: 1) hand to write; 2) hand to take a sheet of paper on the
table; 3) hand to open a lid of a bottle. The choice of the three
tasks derived from a previous empirical study of handedness in
1600 subjects (Schmidt & Höfke, 1989).The observer that rated
the children was blind with respect to the presence or absence
of behavioural problems. Then, each child was classified as
right-consistent, left-consistent, or non-consistent. To be con-
sistent, the child had to perform the three tasks with the same
Continuous Visual Attention Test (CVAT)
The CVAT computer program was developed by Schmidt
and Manhães (2001) and approved for clinical use. The subjects
are required to press the space bar of a microcomputer when a
specific visual target stimulus appears. The test starts with in-
structions and a practice session. The respondents press the
space bar for the correct target as fast as they can. There are 6
blocks, with 3 sub-blocks each of 20 trials (two figures pre-
sented, whether targets or not). For each block, the sub-blocks
have different inter stimulus time intervals (ISI): 1, 2, or 4 sec-
onds. The order of the ISIs varies between blocks. Each stimu-
lus is displayed for 250 milliseconds. The total test takes 15
minutes to complete. The types of measures include: omission
errors (OE), commission errors (CE), reaction time of correct
responses (RTC), and variability of reaction time (VRT). This
standardized test has a number of advantages over other tests,
especially in relation to the norms of the variables derived from
the test. Recently the CVAT was applied as an activation tool in
a functional neuroimaging study (Schmidt et al. 2008).
First Study: Validit y of a Teacher Scale for Attention
The checklist presented high internal reliability as indicated
by Cronbach’s alpha coefficients (α = 0.96). Elimination of any
of the items from the scale caused little change in α. Four fac-
tors were extracted: Factor 1—Hyperactivity/Impulsivity (ex-
plained variance = 36.3%); Factor 2—Inattention (explained
variance = 11.4%); Factor 3—Social isolation (explained vari-
ance = 5.2%); Factor 4—Self-confidence (explained variance =
Second Study: H andedness and Attention Prob lems
Sixty-eight children (28% of the total sample) were included
in the behavioral/attention problem group. The comparison
group included 171 children. The two groups did not differ with
regard to age (t = 0.99; df = 159; p = 0.32). In contrast, the
number of males was found to be greater in the ADHD group as
compared to the comparison group (qui-square = 42.956; df = 1;
p < 0.001).
There was not any significant association (qui-square = 0.558;
df = 1; p = 0.27) between the presence of behavioral problems
and the number of right-consistent and non-right-handers (left
consistent and non-consistent children). However, when the
analysis was done considering only right-consistent and left-
consistent children, the association reached significant levels
(qui-square = 4.664; df = 1; p = 0.03). This result can be ex-
plained by the higher number of consistent left-handers in the
ADHD group as compared to the comparison group. Therefore
all subsequent analyses were done considering only right and
left consistent children. The ANOVAS on the indices for each
factor showed a significant effect of handedness on F1 (F =
5.449; df = 1/159; p = 0.02), but not on the other factors: F2 (F
= 0.996; df = 1/159; p = 0.32); F3 (F = 0.731; df = 1/159; p =
0.39); F4 (F = 2.639; df = 1/159; p = 0.11). These data indi-
cated that left-handers show greater problems in the impulsive-
hyperactivity domain as compared to right-handers.
Third Study: Visual CPT and Handedness
Forty-two participants were matched for the analysis of the
Continuos Performance Tests. Anova (s) on the standardized
scores indicated a significant effect of attention problems on
performance in the following parameters of the CVAT (OE: F
= 8.09; df = 1/24; p = 0.009; CE: F = 5.46; df = 1/24; p = 0.03;
VRT: F = 4.80; df = 1/24; p = 0.04). No significant difference
between the control and the ADHD groups was found for the
reaction time. A significant handedness effect was found only
for the variable CE (F = 4.85; df = 1/24; p = 0.04). In both vis-
ual and audio continuos tests, left-handers with attention prob-
lems showed the greatest number of errors and normal dextrals
the lowest number of errors. Fourteen participants were match-
ed for the analysis of a Continuous Auditory Attention Test.
Anova (s) on the standardized scores indicated a tendency for a
significant effect of attention problems on the performance of
the CAAT, indicating that the presence of attention problems
worsens the performance of the audio CPT as seen in the visual
The first study indicates that the components of the scale can
be viewed as an internally reliable instrument for obtaining
quantified information from teachers. Empirical analysis dem-
onstrates that there is no internal discrepancy in the item con-
tent of the checklist. High internal consistency is a prerequisite
of validity (Guilford, 1956; Nunnally, 1978). Arrindel and En-
dle (1985) claimed that stable factors required the sample to be
approximately 20 times larger than the number of factors. Ac-
Copyright © 2013 SciRes. 31
S. L. SCHMIDT ET AL.
cording to these authors, variable-subject ratio is not important
compared to the ratio of sample size to factors. Therefore, only
if reliable factors are to be considered, a conservative approach
requires that the number of factors in the study never be greater
than 11. As the study shows four factors, the hypothesis that the
factors are reliable is confirmed. In support of the hypothesis of
construct validity, the number of items of each checklist could
be expressed by a smaller number of factors, which are psy-
The second study shows that the number of boys suffering
from ADHD is higher than the number of girls. The same result
has been reported by many other researches (e.g., Gershon,
2002; Quinn, 2008; Stefanatos & Baron, 2007). Moreover, the
data show that hyperactivity/impulsivity is related to handed-
ness, because left-handers present more problems in impulsive
behaviour than right-handers. A similar finding was reported by
Rodriguez and Waldenström (2008). The number of left-hand-
ers is higher than expected in the ADHD problems group. Our
study assesses handedness by direct observation of the children,
which lends much more credence to the handedness data. Fur-
thermore, the assessment of behavioural problems was done by
means of a culturally adapted checklist (Carvalho, Manhães, &
Schmidt, 2012). Therefore, our results suggest that the influ-
ence of consistency of hand use in attention disorders seems to
be a stable finding that is not restricted to western countries.
The handedness effect was confirmed by the data derived
from the CVAT study. Our results show that the presence of
attention problems has a significant effect on the performance
of the visual CPT. All parameters of the CPT were affected by
the presence of attention problems, except reaction time. A
handedness effect was restricted to one parameter, i.e. com-
mission errors. Left-handers with attention problems show
greater impairment in commission errors as compared to right-
handers. Commission error is a parameter that is commonly
viewed as a measure of impulsivity. Moreover, when the nor-
mal group was analyzed separately, the handedness effect still
remained for the commission errors. This may indicate that
even in normal children, consistent left-handers are more im-
pulsive than consistent right-handers.
The influence of handedness on attention can be interpreted
in the context of the asymmetry of the neurobiological sub-
strates of attention. The neural processing of attention is known
to be asymmetrical (e.g., Rolfe, Hausmann & Waldie, 2006;
Schmidt et al., 2008) and left-handers are thought to have less
marked hemispheric asymmetries than dextrals (Bishop, 1990;
Schmidt, Oliveira, Krahe, & Filgueiras, 2000). In particular,
subjects suffering from ADHD were found to show alteration in
the normal pattern of asymmetries in the basal ganglia and
frontal lobes (Castellanos et al., 2002; Swanson et al., 2007).
Therefore, our data suggest that consistent left-handed subjects
show greater probability to develop ADHD as compared to
right-handed subjects since a significant number of them do not
present the normal patterns of brain asymmetries that are
needed for the neural processing of attention.
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