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RESEARCH PAPER
Perceptual-motor coordination in persons with mild intellectualdisability
ELI CARMELI1, TAMAR BAR-YOSSEF2, CLAUDETTE ARIAV2,3, RAN LEVY2 &
DARIO G. LIEBERMANN1
1Physical Therapy Department, Sackler Faculty of Medicine, Tel Aviv University, 2Neve Ram Institute for People with Special
Needs, Israel, and 3Flieman Geriatric Medical Center, Haifa, Israel
Accepted February 2007
AbstractBackground. There is limited experimental evidence to support the view that individuals with intellectual disabilities (ID)have a deficit in motor control. This work is a first attempt to evaluate their motor coordination.Purpose. The study assessed the relationship between cognitive ability and sensorimotor integration. The clinical hypothesisis that adults with ID fall below non-ID adults in motor skills that involve hand-eye coordination.Method. A group of 42 adults with ID (ID group) was compared to 48 age-matched typical adults (TA) using a mixedexperimental design (‘Task’ as the within-subjects factor and ‘Group’ as the between-subjects factor). Participants performedthe following tests twice: Box-and-Blocks, 25-Grooved-Pegboard, Stick Catching and overhead Beanbag-Throw. Pearsoncorrelations and ANOVAs were used to test the hypothesis (p� 0.05).Results. As expected, TA outperformed the ID group in all tests regardless of the hand used during for the assessment.However, TA individuals scored significantly better with one hand (i.e., the preferred and dominant hand) as opposed topersons with ID, who exhibited no hand preference. Test-retest correlations among the first and second assessment scoresyielded moderate-strong coefficients, depending on the type of test (Box-and-Blocks¼ 0.92 and 0.96, 25-Grooved-Pegboard¼ 0.69 and 0.83, Stick-Catching¼ 0.88 and 0.94, Beanbag-Throw¼ 0.58 and 0.91 for ID and TA, respectively).Discussion. Difficulties in the integration of perceptual information into motor action may result in inadequate solutions todaily motor problems. As it stems from our results, intellectual disability relates to inability to integrate visual inputs andhand movements. In people with mild ID such inability is observed using both hands (i.e., they show no hand preferences).Poor perceptual-motor coordination might have a functional significance in that it may lead to exclusion from vocational andrecreational activities, and a decreasing competence of ADL. Assessing coordination in adults with ID may contribute tounderstanding the nature of the ID condition and may encourage an early rehabilitation.
Keywords: Intellectual disability, hand preference, hand-eye coordination
Introduction
The strong relationship between healthy lifestyle and
life expectancy is widely recognized [1,2]. Such a
relationship could be expected also be expected for
the population with intellectual disabilities (ID).
However, adults with ID show signs of premature
aging with a greater tendency towards de-condition-
ing and morbidity [3]. Consequently, they tend to
lose independence more often and eventually be-
come institutionalized. The incidence of ID amongst
the general population of Israel is estimated to be
approximately 3% (i.e., 170,000 people), including
approximately 150,000 individuals with symptoms of
mild ID. Approximately, 40% of adults with ID are
eventually relocated within community programs of
special residential-care centers [4].
Rehabilitation therapists (i.e., physical, occupa-
tional therapists) have important roles within such
institutions. They are responsible for diagnostics and
treatment of the motor impairments of people with
ID [5,6]. More importantly, as a byproduct of
inducing success in daily motor functions they might
be responsible for enhancing some of the intellectual
capabilities. However, the relationship between in-
tellectual disability and lack of success in basic motor
Correspondence: Eli Carmeli, PhD, Physical Therapy Department, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel.
Tel: þ972 36405434. Fax: þ972 3 6405436. E-mail: [email protected]
Disability and Rehabilitation, 2008; 30(5): 323 – 329
ISSN 0963-8288 print/ISSN 1464-5165 online ª 2008 Informa UK Ltd.
DOI: 10.1080/09638280701265398
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skills has only attracted limited attention, parti-
cularly concerning motor coordination in people
with ID [7].
It is reported in the literature that the population
with ID presents premature signs of aging [8,9].
Tasks that are performed under perceptual or motor
constraints such as movement accuracy, reaction
time and speed of movement, may exacerbate the
apparent deterioration of motor performance in
people with ID. Brewer and Smith [10] showed
that control mechanisms mediating speed-accuracy
trade-offs may underlie differences between
retarded-non-retarded populations. Likewise, Inui
and colleagues [11] examined the ability to process
information using a tracking task in adolescents that
have Down syndrome (DS). This group of adoles-
cents showed significantly slower and more variable
reaction times as compared to a matching group of
adolescents with intellectual disabilities, but without
DS. Latash and his colleagues [12] addressed the
apparent ‘clumsiness’ of persons with DS and its
relation to changes in indices of finger coordination,
and concluded that persons with DS have a deficit
in the control of both single- and multi-fingers
movements.
Deterioration in motor performance, however,
may be a main characteristic of aging [13] aside
cognitive impairments [14]. Therefore, we cannot
preclude the possibility that motor outcomes are a
simple expression of the premature aging which is so
often characteristic of people with intellectual dis-
abilities. In order to partially preclude such a
possibility, we selected a sample of participants
composed of a subset of individuals with only ‘mild’
intellectual deficiencies because they were less prone
to suffer the effects of premature aging (i.e., we
reduced this covariate to a minimum).
Cognitive disability, development and motor skill
Motor impairment in people with intellectual dis-
abilities may relate to developmental factors [15].
Unilateral limb-dominance and hand-preference are
related to the specialization of the brain’s hemi-
spheres that occurs during development [16,17].
Arnold and colleagues [18] argued that rather than
showing clear asymmetric patterns with a clear
dominance of one side while moving, people with
ID do not discriminate between the left- or right-side
limbs.
Difficulties in performing hand-eye coordination
tasks bilaterally may underlie some of the difficulties
of adults with mild ID during their activities of
daily living (ADLs). An expression of such cognitive
impairment may be a generally poor motor per-
formance. We focus on the lack of differences
between the two hands and assume that hemispheric
specialization is a key factor in developing manual
dexterity. Normally, such specialization should be
evident in superior performances of the dominant
hand as compared to the opposite hand.
We further assume that poor coordination has a
functional impact on performance that may lead to a
decreasing competence in ADLs and ultimately may
result in exclusion from vocational and recreational
activities. We hypothesize that motor skill of people
with ID fall below the expected for non-ID people.
Four tasks that involve integration of hand move-
ments with visual information are used here in order
to test coordination in adults with mild ID and hand
preference. For this purpose, participants are in-
structed to perform tasks under constraints that
resemble those used in the previous studies (speed-
accuracy in a pegboard test, reaction time in a Stick
Catching test and accuracy in a mentally rotated
environment in a backwards beanbag throw). Their
results are compared to the performances of aged-
matched typical adults.
Furthermore, this study assesses the relationship
between cognitive ability and sensorimotor integra-
tion in adults with and without ID. We explore the
interrelationships between motor performances of
ID people at different times in order to evaluate
reliability and validity scores of the simple hand-eye
coordination tests.
Method
Participants
A group of adults with mild intellectual disability is
compared to an age-matched group in terms of
specific motor tasks performed bilaterally (right and
left hands; dominant hand first). The participants in
the residential home centers usually shared apart-
ments with 3 – 5 residents who are supervised around
the clock by a trained staff person. Medical, health,
welfare, rehabilitation services and recreational activ-
ities are routinely provided by supplementary staff.
The sample consists of permanent residents who
lived in foster homes at two residential care centers.
After being referred to the study by the institutional
health-care professionals, only candidates that vo-
lunteered to participate were considered for the
experimental trials. From a sample population of 418
permanent residents with ID, only 42 participants
with mild ID are included in the current ID group
(28 females and 14 males; mean age¼ 42.2+ 6.22
years; range 31 – 49 years). Three inclusion criteria
were used for selecting participants for the ID group:
(1) Mild intellectual deficiency (IQ¼ 62 – 79), as
diagnosed within 1 – 3 years after birth by IQ-
scores defined by the Wechsler Abbreviated
324 E. Carmeli et al.
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Scale of Intelligence (Harcourt Assessment
Inc., San Antonio; [19]).
(2) Recognized ability to understand basic verbal
communication.
(3) Independence from personnel or from sup-
port services/devices.
Candidates were excluded if they had a clinical
history of neurological disease (e.g., Parkinson’s
disease, stroke, Alzheimer’s disease, neuropathy or
brain surgery) or in the case of any peripheral
neurological sign. In addition, candidates were
excluded if they showed any significant perceptual
deficits (e.g., auditory and/or visual). None of the
participants received narcotic medications at the
time of the experiments.
Similarly, from 213 permanent caregivers who
worked with the ID community, 48 participants are
included in the group of typical adults TA (30
females and 18 males; mean age¼ 45.7+ 5.19 years,
range 22 – 53 years). Participants with ID lived in the
care centers for at least five years prior to being
tested. The volunteers in the TA group work in those
centers in different health care professions (social
workers, caregivers, teachers and nurses).
The study was approved by the Institutional Ethic
Committee of Residential Care Centers under the
administrative control of the Israeli Ministry of
Welfare. Oral consent was obtained from partici-
pants as well as a written consent from their parents
or guardians.
Experimental procedures
Data were collected in two testing sessions separated
by a period of 6 – 8 days. This allowed enough time
for dissociating the second set from the experience
gathered in the first attempt. That is, assessment
values obtained approximately one week apart were
used to test reliability scores. Trials were performed
in a quiet environment that minimized shifts of
attention away from the experimental tasks. The
examiner always provided a first standardized set of
verbal instructions followed by a demonstration of
the motor task. A 10-min practice period was then
allowed. Hand dominance was determined by hand
preference during the warm up trials (3 trials per
task). The dominant hand was the first to be tested in
all cases. Data collection was always initiated with a
‘go’ signal provided by the examiner.
Motor tasks
The reason for testing our hypothesis using the
selected motor tasks was that they included elements
of hand-eye coordination (e.g., hand throwing to
memorized visual targets, fast hand-finger actions in
reaction to a visual events, grasping and transporting
small objects, accurate hand-finger movements).
These tests have been shown to be reliable, they
were simple and easy to implement in field condi-
tions, and fairly close to real-life situations.
Box and Blocks Test (B&B). Performance of B&B
was carried out while the individuals faced towards
the box (546 266 9 cm) located at the center of a
standard table. The box was divided into two equal
compartments by a 15 cm high dividing wall. The
blocks consisted of 100 wooden cubes (2.5 cm3). In
order to evaluate manual dexterity, participants were
instructed to transport a maximal number of blocks
from one side to the opposite side within 15 sec, one
block at a time [20]. Individuals performed first with
the preferred hand and 2 min later they performed
with the opposite hand. Each participant performed
two sets of trials with each hand (four sets in total
in two stages). The B&B test was chosen because it
is a robust test that is known to yield high intrarater
validity and interrater reliability scores (Intrarater
Correlation Coefficient ICC r¼ 0.92 – 0.96 and
an Interrater Reliability Coefficient IRC r¼ 0.78 –
0.92; [21]).
25-Grooved Pegboard Test (PegB). This test was
designed to assess fine manual dexterity and hand/
eye coordination [22]. It consists of a wooden board
with 25 holes. Performers were instructed to insert
25 cylindrical pegs (0.25 cm diameter6 0.8 cm
height) as quickly as possible into the holes, one
peg at a time. Performance time was continuously
measured, even in the event that pegs were dropped
down to the ground. The time to complete the task
was measured twice for each hand. For such a test,
validity and reliability scores reported in the litera-
ture [23 – 25] are moderate-high (ICC r¼ 0.69 –
0.83, r¼ 0.65 – 0.81).
Stick Catching test (StickC). Reaction time (RT in
ms) was assessed using a 2.5 cm wide6 100 cm
length wooden ruler (0.1 cm nominal resolution),
which was held vertically in the direction of the
gravity vector. Upon release, performers were in-
structed to catch the ruler and prevent the free fall
using a pinch-like grasping action. The measure of
the distance obtained from the difference between
the initial and final grasping heights was used as a
measure of reaction time.
According to Newton’s formula (i.e., the time of
flight during a free fall depends on the gravity
constant. Therefore, knowing the falling distance
under gravity conditions implies knowing the flight
time [27]):
Flight time ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi2 �distance ðmÞ=9:81ðm � s�2Þ;
p
Bilateral hand-eye coordination in adult with mild ID 325
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and thus, the free fall distance could indeed provide a
gross measure of visual RT because falling distance
may be translated into the falling time (i.e., flight
time), which is the time it would take the fingers to
move after visually perceiving the onset of the fall of
the ruler [26]. Such a method is just one among
many ways of testing RT, but perhaps the simplest
and most rudimentary. However, because our
sample was randomly selected and enough data
trials were collected, the current method was
assumed as a reliable way to assess RT.
During the measurements, participants sat on a
standard chair while their performing arm was at 308flexion and 208 abduction relative to a zero-arm
configuration (as defined by the fully extended arm
pointing forward). The elbow joint was positioned at
908 flexion while the forearm-wrist was maintained
in a mid-torsion position (between maximal supina-
tion and pronation). The examiner stood next to the
performer and held the ruler at a ‘zero starting point’.
At a random time, the examiner dropped the ruler
and the performer attempted to grasp it. Six
consecutive trials (three per hand) were carried out
with a 15-sec resting interval between measurements.
RT measures provide robust descriptors of the
ability to respond as fast as possible to an unexpected
stimulus, with an intra-rater validity r¼ 0.88 – 0.94
and a test-retest reliability r¼ 0.85 – 0.96 [27].
Overhead Beanbag Throw (BThrow). The goal of this
task was to throw a beanbag (500 gm) over the
shoulder in the direction of a hoop (0.75 m
diameter) located at the center of a 16 1 m
gymnastic mat. The performer stood at a distance
of 2 m facing away from the mat. Each hand
performed six consecutive attempts (12 trials in
total). After every trial, performers got an immediate
knowledge of results. A 0 – 3 scale was used to score
the motor performance whereas a three points score
was given for a throw that ended within the hoop,
two points if the bag partially hit the hoop and later
fell onto the mat and one point if the bag landed
anywhere on the mat without hitting the hoop. A
zero score was given when the beanbag landed
outside the mat. This arm-throwing test was
assumed to test spatial orientation [28], accuracy
and throwing skill. Reported scores of validity and
reliability for ball throwing tests are ICC r¼ 0.58 –
0.91 and r¼ 0.75 – 0.92 for test-retest sessions [29].
Mental rotation is among the different cognitive
skills required for a success in such a task. This has
been specifically addressed in the early experiments
of Shepard and colleagues [30,31]. These authors
showed that gradual mental rotation of an object
increases the response time during the actual
performance, whereas anticipatory mental rotation
of the same object (before starting the performance)
reduces the response time. Difficulty in mentally
rotating objects may be one more expression of
cognitive impairment. The overhead throwing task as
performed here puts such a cognitive skill to the test.
Analysis
Data analyses included multiple analyses of variance
(ANOVA) and Pearson correlations between vari-
ables. Hand dominance across tests (right vs. left)
and group differences (TA vs. ID) were determined
by introducing ‘Hand’ as a within-subjects factor and
‘Groups’ as the between-subjects factor. Correlation
coefficients were calculated among the four tests to
determine the inter-correlation coefficients. Descrip-
tive statistics were also calculated for relevant
demographic variables, including the mean, standard
deviation and 95% confidence intervals for each
dependent variable, with age and gender as grouping
factors. A SPSS-v10 (SPSS Inc., Chicago, IL, USA)
package was used for the statistical assessment of the
hypotheses. The confidence level was set at p� 0.05.
Results
Differences between groups in motor tasks that involve
hand-eye coordination
Performance scores for ID participants were sig-
nificantly lower and less consistent in comparison to
TA individuals, in all four tests (see Table I). TA
individuals showed not only superior performances
overall, as expected, but also significantly better
results for the dominant hand, and therefore, this
hand seem to be the preferred one (F[1,88]¼ 72.45;
p5 0.001). Notably, the ID group presented motor
performances of the dominant hand that were not
significantly different from the opposite hand
(F[1,88]¼ 3.581; p¼NS) suggesting that ID may
have an undefined hand preference.
Repeated sessions showed strong correlations for
the B&B test (ICC r¼ 0.92 – 0.96), moderate for the
PegB test (ICC r¼ 0.69 – 0.83) and Stick Catching
test to assess reaction times (ICC r¼ 0.88 – 0.94),
and inconsistent but moderate-high coefficients for
the BThrow test (ICC r¼ 0.58 – 0.91). The incon-
sistency in the correlation scores might be attributed
to the larger variance observed for the result obtained
in this task. The task enables discrimination among
individuals with ID because it includes some domi-
nant cognitive components, as it will be discussed
in the next section.
Strong pair wise inter-correlations ranging
r¼ 0.76 – 0.98 (all significant at p5 0.05) were
observed between the four tests for both groups, as
shown in Table II. However, the coefficients for data
grouped by gender and hand preference showed
326 E. Carmeli et al.
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strong correlations between all four hand-eye co-
ordination tests performed with the dominant and
preferred hand, but only for the TA group (r¼ 0.80 –
0.92, p5 0.05).
It is worth noting also that given the similarities
between B&B and PegB tests the strong relationship
found (r¼ 0.98, p� 0.001) implies that these two
tests may be different expressions of a similar sensori-
motor ability that underlies the performance. Hence,
one or the other might be considered redundant.
Discussion
Motor skill in general is required throughout life for
adaptation to our daily environment, while manual
skill in particular is essential for achieving indepen-
dence in many ADL [32]. Poor motor coordination
might have functional impacts and may lead to
exclusion from vocational and recreational activities
and decreasing competence of ADL (activities of
daily living). Our results however suggest that people
diagnosed as having mild intellectual disabilities
perform poorly manual tasks that require interactions
between hand motion and visual inputs.
Cognitive disability, development and motor skill
We showed here that hand specialization is not
obvious even in persons with a mild intellectual
disability. Our sample of participants presented no
advantage in using one hand over the other, and the
findings may provide support for the suggestion that
people with intellectual disabilities have no func-
tional differentiation between hands (i.e., a bilateral
symmetry) during simple motor functions. Lack
of a clear pattern of lateralization has already been
reported [33].
We might speculate that this is related to their
undefined interhemispheric brain specialization.
That is, differences between ID and TA groups
might be a reflection of a developmental setback in
the former group.
In the present study, participants were tested
under task constraints that resembled those in the
previous studies (speed-accuracy in the pegboard
test, reaction time in the Stick Catching test and the
Backwards Beanbag throw), but in all these tests,
their performance was poor as compared to the
performances of an age-matched group of controls.
Since deterioration in motor performance under the
previous constraints is also is one main characteristic
of aging [13] aside cognitive impairments [14], we
cannot preclude the possibility that the observed
results were an outcome of premature aging,
characteristic of people with intellectual disabilities,
rather than a correlate of intellectual disability.
Motor performance of people with ID without vision
As implied in previous paragraphs, conditions that
challenge the sensorimotor abilities of people with
intellectual disabilities may allow for discrimination
among individuals at different levels.
The visual occlusion paradigm during motor
performance has been widely used to assess the
effect of continuous or intermittent feedback on the
execution of movement. Occlusion of visual input
may lead to the use of internal representations of the
Table I. Means, SD and confidence intervals for the Box and Blocks Test (B&B), 25-Grooved Pegboard Test (PegB), Stick Catching test
(StickC) and Beanbag Throwing test (BThrow) by gender subgroups (Male/female) and hand dominance (Dominant D/Non-dominant,
ND).
ID group TA group
Groups D/ND D/ND D/ND D/ND
Test Male Female Male Female
B&B (# blocks) 8+ 2/6+ 4 10+ 2/7+3 6+2/5+ 2* 6+ 2/5+2*
PegB (sec) 59+ 9/73+ 11 52+ 7/64+9 49+6/62+ 7* 47+ 6/51+7*
StickC-RT (ms) 247/263 251/267 235/257* 240/274*
BThrow (points) 4+ 3/2+ 2 3+ 1/2+2 2+1/6+ 2* 5+ 1/2+1*
*p�0.05.
Table II. Pair wise Pearson correlation coefficients between for the
different field tests for the TA and ID groups: Box and Blocks
(B&B); 25 Grooved Pegboard test (PegB); Stick Catching reaction
time test (StickC); and Beanbag Throw task towards a target
(Bthrow test.)
Groups Tests B&B PegB StickC BThrow
Typical B&B 1 – – –
Adults PegB 0.98* 1 – –
StickC 0.89* 0.90* 1 –
BeanB 0.84* 0.88* 0.76* 1
Intellectually B&B 1 – – –
Impaired PegB 0.98* 1 – –
StickC 0.86* 0.88* 1 –
BeanB 0.88* 0.90* 0.92* 1
*p�0.05.
Bilateral hand-eye coordination in adult with mild ID 327
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environment. An internal visual representation could
indeed be used to activate and modulate previously
acquired motor plans with little or no feedback. Do
individuals with ID lack this ability during aiming
tasks? The findings here show that this may be the
case and such a possibility is supported by earlier
literature [34,35]. The beanbag throw in our experi-
mental trials was carried out backwards, to a
previously seen target. Thus, it posed a cognitive
challenge to our participants with mild ID because it
required the ability to perform an accurate task
without visual perception of the location of the
target. We showed that lack of continuous visual
input affected the performance of people with mild
intellectual disabilities.
Intellectual disability and mental rotation
Although the beanbag throwing task may be see-
mingly simple, the sensorimotor ability required for
its performance is the ability to locate objects relative
to rotated body coordinates within a fixed reference
frame. This may be a challenge for individuals
with ID. Accurate backward throws involve the
transformation of joint coordinates that define the
appropriate arm – hand configuration into spatial
coordinates of the mentally visualized target. Such a
task involves also an adjustment of motor commands.
During a normal throwing task, arm extension may
be appropriate because the performer faces the target.
However, when the performer faces in the opposite
direction (a 1808 rotation of the body) a backward
throwing movement is required because the target is
located behind, and thus, arm flexion is the appro-
priate action. Participants in the present study often
failed to make such a coordinate transformation in
the correct target direction. Thus, as it stems from
the results of the present study people with mild
intellectual disabilities lack the fundamental ability to
rotate mentally the location of an object in space.
Furthermore, they fail to integrate an internal visual
image into the appropriate motor commands.
Clinical relevance
We have shown in a sample of adults with ID that
upper body (hand – eye) coordination is poor,
particularly when a quick response to perceptual
(visual) stimuli is required. An early detection of
deficits in coordination, as assessed by the simple
tasks used in the present study, is utmost essential for
an accurate and optimized rehabilitation process that
targets functional abilities. In addition, assessing
perceptual-motor coordination may contribute to
understand the nature of ID because poor hand-eye
coordination is an expression of intellectual disability
[36]. In this regard, the beanbag throw poses a
challenge because it may be associated with the
mental rotation of a previously acquired visual
representation of the environment. Such motor task
may enable to discriminate among individuals at
different stages of the rehabilitation process because
it emphasizes critical cognitive elements related to
success in the performance of ADL.
Conclusions
Motor assessments using hand – eye coordination
tasks may reflect the status of people diagnosed as
having mild intellectual disabilities. Such assess-
ments may allow for designing early rehabilitation
programs specific to the individuals. Rehabilitation
protocols should thus include specific motor tests as
part of the common cognitive assessments performed
in residential care centers.
Acknowledgements
The authors wish to thank Mr S. Bar-Chad from the
Neve-Ram Institute for People with Special Needs,
Rechasim, Israel, and Prof. J. Merrick from the
National Institute of Child Health and Human Devel-
opment affiliated with the Ministry of Social Affairs of
Israel, for his assistance during the performance of
the field tests. Finally, we gratefully acknowledge the
insights provided by Dr M. Wertheim.
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