Journal of Autism and Developmental Disorders, Vol. 26, No. 6, 1996
Hand Preference and Hand Skill
in Children with Autism
K. M. Cornish ~
University of Leicester
I. C. M c M a n u s
University College, London
Hand preference and hand skill was assessed in two broad age groups of children
with autism, children with learning disabilities, and control schoolchildren. The
first group comprised children ages 3-5 years and the second group of children
ages 11-13 years. Degree of handedness remained relatively stable across age
groups, particularly within the autistic and learning-disabled populations. The
main difference was between the subject groups, with the normal controls more
lateralized than either the children with autism or children with learning
disabilities. As with degree of handedness, consistency of handedness also differed
significantly between subject groups with the normal controls more consistent in
their hand preference than the other two groups. In addition, younger children
were less consistent in their hand preference than older children. However, the
present study found no evidence of a dissociation of hand skill and hand
preference in children with autism compared to children with learning disabilities
and normal developing children.
INTRODUCTION
An increased incidence of left handedness (LH) in children with
autism compared to children in the normal population is well documented
in the literature (e.g., Gillberg, 1983; Leboyer, Osherham, Nostem, &
Robertou,x, 1988; Tsai, 1983; Soper et al., 1986), and as such is consistent
1Address all correspondence to Kim Cornish, Room B556, Faculty of Medicine, B Floor,
Medical School, Queens Medical Centre, Nottingham NG7 2UH, United Kingdom.
597
0162-3257/96/1200-0597509.50/09 1996PlenumPublishing Corporation
598
Cornish and MeManus
with the high prevalence frequently reported in children with moderate to
severe learning difficulties (e.g., Pipe, 1988). A theory explaining this difference which continues to receive considerable attention is that of Satz
and colleagues (e.g., Satz, Orsini, Saslow, & Henry, 1985; Satz, Soper, &
Orsini, 1988; Soper & Satz, 1984). They argue that brain insult sustained
early in development results in manual dominance switching from the right
to the left hand, and that despite brain insults occurring randomly to right
or left hemisphere, the outcome is nevertheless asymmetric since most individuals are left hemisphere dominant, and therefore "natural" right-handers are more likely to switch hand preference to become "pathological
left-handers" (PLH) than vice versa (Satz, 1972). Additionally other aspects
of lateralization involving speech and language may be affected (e.g., Satz
et aL, 1985).
The linking of left-hemisphere insult, learning disability, and raised
LH has become attractive in the autistic literature since the primary deficits
associated with autism seem to be those requiring left-hemisphere function
(i.e., language comprehension, vocabulary, and phonology), whereas righthemisphere functions (i.e., visuospatial skills) remain relatively unaffected
(e.g., see Fein, Humes Keplin, Lucci, & Waterhouse, 1984, for a review).
However clinical studies in children with autism have consistently failed to
confirm this hypothesis, reporting either bilateral damage (e.g., Tsai & Stewart, 1982) or right hemisphere insult (e.g., Gillberg, 1983).
As well as having an increased rate of LH, children with autism have
also been reported to have a higher incidence of ambiguous or inconsistent
handedness (AH), an effect originally claimed to be specific to the condition (e.g., Soper et al., 1986). AH refers to reduced consistency of hand
preference within tasks (e.g., preferring to carry out task A with the right
hand on one occasion and with the left hand on a second occasion), and
should not be confused with reduced degree of hand preference between
tasks, in which one hand is preferred for task A and the other hand preferred for task B. The two are however partially confounded statistically
(McManus, 1996; McManus, Murray, Doyle, & Baron-Cohen, 1992). According to Soper et al. (1986); AH is distinct from PLH and probably resuits from early bilateral hemisphere deficit rendering neither hemisphere
sufficient for manual dominance. A review by Satz, Green, and Lyon (1989)
estimated that AH accounts for approximately 40% of the handedness observed in individuals with autism and individuals with learning difficulties
but is relatively rare in normal populations above the age of 4 years. However, in a study by McManus et al. (1992), AH was significantly increased
in children with autism compared to a mentally retarded control group and
normal control group, even when degree of handedness, age, and mental
age were taken into account. It should also be noted that differences in
Hand Preference and Hand Skill
599
hand preference (be they direction, degree, or consistency) and assessed
typically by reaching, should not be confused with differences in hand skill,
assessed typically by a task such as the Annett Pegboard, and in which one
can also assess the direction of the more skillful hand, and the degree of
difference ~between the hands.
A third anomaly of handedness recently reported in children with
autism is a dissociation between hand skill and hand preference (McManus
et aL, 1992). Children with autism demonstrated a high level of discordance
between hand preference and hand skill, 50% of them preferring to use
the hand which was actually less skilled on the Annett Pegboard task (Annett, 1970). In contrast, almost all subjects in the control groups showed
greater hand skill with the preferred hand.
A problem of past research highlighted by Satz et al. (1985) is the
tendency to use inadequate methodology in determining hand preference
in autistic samples. In particular, the failure to assess AH using repeated
testing within preference items. The present study employed a standard performance battery (McManus et al., 1988) that measured consistency and
degree of handedness.
The McManus et al. study matched children with autism and controls
solely on the basis of mental age. In consequence, the children with autism
were about 11 years old, considerably older than the normal controls (mean
age 4.9 years). The present study was designed principally to measure the
handedness of young children with autism and to assess their patterns of
hand usage (and indeed to assess the feasibility of measuring handedness
in that group) (Fein et aL, 1984). As such it can be seen as an extension
of the McManus et al. study, so that when combined with it, along with
group of older control subjects, a complete factorial design would arise by
age and diagnostic group. It should therefore be possible to tell whether
hand usage in younger autistic children is also atypical, or whether the pattern is only present in the older children.
METHOD
The present study consists of a development and an extension of the
work of McManus et al. (1992); in particular additional groups of subjects
were tested and then combined with the original subjects of McManus et al.
(1992) to allow a more comprehensive analysis.
600
Cornish and McManus
Participants
Participants were in two broad age groups: Younger children, in the
range 3-5 years (children with autism, age 4-5 years, n = 15; children with
learning disabilities, age 4-5 years, n = 14; and control schoolchildren at
ordinary schools, age 3-5 years, n = 65); and Older children, in the age
11-13 years (children with autism, age 12-13 years, n = 20; children with
learning disabilities, age 11-12 years, n = 12; and control schoolchildren
at ordinary schools, age 12-13 years, n = 24). Some of the younger control
children, along with all of the older children with learning disabilities and
children with autism are the same as those reported previously in McManus
et al. (1992).
All the autistic children were receiving special education in units for
children with autism and were diagnosed according to established criteria
(e.g., Rutter, 1978). None of the participants had any obvious physical
handicap that would influence their hand preference.
The new participants in the present study were resident in Northamptonshire, and in all cases were tested individually in their schools.
Intellectual level in the younger children in all groups who had not
been assessed in the previous study was measured by the Merrill-Palmer
Scale of Mental Tests. Tests of intellectual ability were not administered
to the older group of controls since the Merrill-Palmer is not suitable for
that age group, and instead they were assumed to be typical of children in
general of their age.
Tasks
Hand preference was assessed by a battery of 10 symmetrically presented unimanual preference tasks (e.g., coloring a square, eating with a
spoon, picking up a sweet) (based on the items of McManus et al., 1988).
The battery was repeated three times during the course of the testing
session. Responses were scored as Right (R), Left (L) or Bimanual/Mixed
(B). For each participant a Laterality Index (LI) was calculated across
all items as: 100 (n(R)-n(L)/n(R)+n(L)+n(B)). The LI was partitioned
into measures of direction of hand preference (LI < 0 for left handed;
LI > 0 for right handed) and degree of hand preference (ILII, the absolute laterality index). Consistency of hand preference was calculated
across all pairs of replications of each item (lst with 2nd, 2nd with 3rd,
1st with 3rd), two tasks were considered consistent only if the right hand
was preferred on both occasions or the left hand was preferred on both
occasions. Since in the present paper only 10 items were scored, whereas
Hand Preference and Hand Skill
601
in McManus et al. (1992), 13 items were scored, there are minor differences in the results shown in Table I from those reported previously. It
should be noted here that since, particularly among the younger subjects,
a moderate number of bilateral or mixed preferences were given, the result is that laterality scores can take any value in the range 0-100%; this
is in distinction to the slightly different definition used by McManus et al.
(1992), where of necessity scores are constrained to the range 33-100%.
It should also be noted that Table I of McManus et al. (1992) contains
three minor typographic errors (4.3 should be 7.5 for the SD of average
time on pegboard in the autistic group; and 9.9 and 9.6 should be reversed in the penultimate line), and the table in the present paper corrects those errors.
H a n d skill asymmetry was assessed using the Annett Pegboard (Annett, 1970). This measured the difference in time for the left and the
right hands to move a row of 10 dowelling pegs from one set of holes
to another. The pegboard task was carried out twice with each hand,
either in the order RLLR or LRRL. Several measures of performance
were calculated. The average time to carry out the four tasks, the average
time with the right and with the left hand, the difference between the
average time with the right and the left hand, and the average time for
the better hand and the worse hand. Additionally a standardized Skill
A s y m m e t r y Index (SAI) was calculated using the formula (100(LR ) / ( L + R ) for the difference between the right and left hands, and additionally an analogous score (see Table I ) w a s calculated for the
difference between the better and the worse hand. Finally, the direction
of skill asymmetry was calculated as right if SAI was greater than zero
and left if SAI was less than or equal to zero. Preference and skill were
defined as concordant if the direction of skill lateralization was the same
as the direction of preference lateralization.
~S~TS
Intellectual Level. The young controls had a mean (SD; range; n) score
on the Merrill-Palmer of 76.2 (13.6; 31-94; n = 43, 2 subjects would not
cooperate with testing), the young children with autism had a mean of 47.2
(21.4; 26-81; n = 13, 2 subjects could not be tested), and the children with
learning disability had a mean of 23.4 (8.4; 4-42; n = 14). A comparison
between the groups using one-way ANOVA showed highly significant differences overall, F(2, 67) = 75.9, p < .001, with all three groups differing
from all other groups using a Scheff6 post hoe comparison.
6.15
74.7
(26,5)
69,8
(27.5)
23.3
(4.7)
21.9
(4.9)
24,7
(5.0)
21.6
(4.6)
25,1
(5.1)
6.2
(6.2)
Direction of handedness (% left-handed)
Consistency of handedness
Degree of handedness a
Average time on pegboard (seconds)
Right hand (time on pegboard)
Left hand (time on pegboard)
Better hand (time on pegboard)
Worse hand (time on pegboard)
Pegdiff (L - R) (time on pegboard) e
II
II
6.1
(11.6)
34.8
(12,7)
28.3'
(9.5)
33.5
(12.9)
29.6
(9.9)
31.6
(10.8)
45,4
(31.7)
53.0
(3.1)
33,3
"=
0.0
r
2.7
(9.2)
51.6
(10.2)
44.7
(11.6)
50.4
(11.5)
47.0
(11.7)
48.2
(10.7)
48,9
(32.2)
52.4
(32.7)
r
Younger children
II
0.0
II
II
63.1
(15.4)
15.0
~
3,0
(5.5)
11.8
(1.2)
10.5
(1.0)
11.5
(1,3)
10.8
(1.2)
11.2
(1.1)
3.6
(11.9)
24.3
(8.9)
19.6
(6.3)
21.3
(8.9)
22.6
(7.2)
21.9
(7.5)
79.1 ~ 48.0
(30.9)
(23.5)
82.8
(31.1)
~
1,4
(12.4)
30.1
(7.1)
24.5
(3.4)
27.4
(4.0)
272
(Z9)
27.3
(4.8)
49.9
(25.1)
75.5
(9.6)
25.0
~-
Older children
Table I, Comparison of Participants by Group ~
ns
< .001
< .001
< .001
< .001
< .001
< .001
< .001
< .01
< .003
< .001
< .001
< ,001
< ,001
< .001
ns
< .01
ns
=
ns
< .001
< .001
< .02
< .001
< .003
ns
ns
< .01
x
Significance tests
(nominal significance-level)
e'L
m-
!
O
2.8
(3.0)
17.2
Skill asymmetry index (SAI)g
Discordant hand preference and skill (%)
20.6
3.9
(7.7)
10.1
(8.0)
0.6
(1.2)
20.0
30.8
5.4
(2.9)
2.3
(8.0)
7.8
(5.2)
a Numbers in parentheses are standard deviations.
bTwenty controls from McManus et ai. (1992).
c Data from McManus et al. (1992).
d Mean time for all four trials, two using the left hand and two the right hand.
e Expressed as LPeg - RPeg.
fExpressed as 100" (Worse - Better)/(Worse + Better).
gExpressed as 100" ( L P e g - RPeg)/(LPeg + RPeg).
7.5
(4.4)
Better hand vs. Worse hand (time on pegboard) f
50.0
1.3
(6.1)
10.0
(7.1)
16.7
0.1
(8.1)
9.6
(7.4)
<
as
ns
.01
ns
< .001
ns
us
ns
ns
gl,
604
Cornish and McManus
Table I provides a summary of results across age groups and between
subject groups. Statistical analysis was by analysis of variance in all cases
except the two binary dependent variables, direction of handedness and
discordant hand preference and skill, where logistic regression was used
instead; the two methods are however equivalent in their interpretation.
Table I contains 33 statistical tests, not all of which are totally independent,
and we therefore assume there are about 20 degrees of freedom overall.
We have used a conventional (adjusted) alpha level of .05. However a strict
interpretation of the table using a Bonferroni correction would accept as
significant only those results meeting an unadjusted significance level of
.05/20 = .001. In practice this produces few substantive changes in the interpretation of the data.
Hand Preference. Eight of 35 (23%) children with autism, 3 of 26 (11.5)
children with learning disability, and 4 of 90 (4.4%) of control children showed
a left-handed preference. Logistic regression of handedness, showed no main
effect of age, X2(1),p = .04, ns); a significant main effect of group, X2(2) = 9.24,
p = .010; and a significant Group x Age interaction, ~2(2) = 9.01, p = .011,
none of which would be significant applying a Bonferroni correction. The incidence of left handedness in the groups is however consistent with those reported elsewhere (see Fein et aL, 1984).
Degree of Handedness. This differed significantly between the three
subject groups, F(2, 145) = 14.26, p < .001, with the normal controls more
lateralized than either the children with autism or the learning-disabled controis. The latter two groups did not differ in their degree of lateralization,
F(1, 57) = 0.134, ns). There was no main effect of age, F(1, 145) = 1.445,
ns), nor an interaction with age, F(2, 145) = 0.278, ns).
Consistency of Handedness. This differed between the groups, F(2,
145) = 9.255, p = .001, with controls being more consistent than the other
two groups; there was no significant difference between children with
autism and children with learning disability, F(1, 57) = 0.937, ns). Younger
children were less consistent than older children, F(1, 145) = 6.334,
p = .013, although there was no interaction between age and group, F(1,
145) = 0.783, ns (see Table I). Again a Bonferroni correction would nullify
the age effect.
Hand Skill Asymmetry. The average time taken to complete the Annett
Pegboard differed significantly between the groups, F(1, 143) = 110.18,
p < .001, with the normal controls significantly faster than the autistic group
and the learning disability group at each age group, the interaction not being
significant after taking the Bonferroni correction into account. The differences
betweerf groups at the younger age remain significant after taking differences
in Merrill-Palmer into account using analysis of covariance, F(2, 64) = 13.4,
p < .001. The distribution of the L-R difference scores did not differ across
Hand Preference and Hand Skill
605
the three groups, F(2, 143) = 2.09, ns), as neither did the SAI, although the
difference between the better and worse hand was significantly greater in the
autistic group compared to the control groups, F(2, 145) = 4.65, p = .011,
before Bonferroni correction). Analysis of just the younger children using
Schefft's test showed that autistic children were significantly (p < .05) faster
than learning-disabled controls and slower than normal developing controls
on total pegboard time, time with right and with left hand, and with better
and worse hand; however there were no differences between groups in difference scores between hands.
Skill-Preference Concordance. In each of the groups there were individuals who showed discordance between the direction of hand preference
and the direction of hand skill (see Table I). However, logistic regression
showed that there was no main effect of age, X2(1) = 2.03, ns, there was
no significant effect of group, Z2(2) = 3.66, ns, and there was no significant
Group • Age interaction, Z2(2) = 3.41, ns.
DISCUSSION
This study shows clearly that handedness, both measured as preference
and as skill using the Annett Pegboard, can straightforwardly be measured in
children with autism and children with learning disorders who are as young as
4 years of age, and it is clear that the younger children with autism are slower
overall on the pegboard task, although not as slow as the children with learning
disorders, even after taking Merrill-Palmer scores into account.
Hand Preference. In accordance with previous findings (e.g., Soper et al.,
1986), the present study found a nonsignificant increase in the incidence of
left-hand preference in children with autism and children with learning disabilities, although the number of left-handed autistic children was twice that of
learning-disabled children and five times the incidence of normal developing
children; however it must be said that the incidence of LH in our control group
(4/90; 4.44%) was somewhat lower than is typically found in other studies. One
possible explanation of the raised incidence of LH is that children with autism,
in addition to the learning disabled, demonstrate a high incidence of PLH to
the extent suggested by Satz and colleagues (e.g., Satz et aL, 1989). However,
as noted by Bishop (1990), observing an increased rate of LH may not be indicative of pathological handedness but may be attributable to other factors,
including developmental motor delay. Indeed, in the present study when hand
preference is assessed in the two age groups separately, left-handed preference
decreases from 33% in the younger children with autism to 15% in the older
children with autism; a level that falls within the normally accepted range (albeit
an incidence which is three times that in our normal controls).
606
Cornish and McManus
Degree of Hand Preference. Degree of hand preference remained relatively
stable across age groups, particularly within the autistic and learning-disabled children. Although nonsignifi~mt the increase in degree of hand preference from 3
years to 12 years in the normal controls is consistent with findings reported elsewhere (McManus et aL, 1988). As with consistency of hand preference, degree
of hand preference did not differ significantly between children with autism
and children with learning disabilities but was more lateralized in the normal
controls. The findings of a reduced degree of hand preference in the learningdisabled population has been reported in previous studies (e.g., Batheja &
McManus, 1985) and would be anticipated if degree of laterzlization is dependent upon experience of tasks lateralized to one hand (such as writing),
or if there is less reinforcement of performance carried out by the better hand.
This process is obviously not specific to autism per se but is more likely to be
a nonspecific consequence of a generalized learning disability.
Consistency of Hand Preference. Children with autism and children with
learning disability were significantly less consistent in their handedness than
were normal developing children. In addition, younger children showed a tendency to be less consistent in their hand preference than older children, although examination of Table I shows that while the normal controls remain
at a comparably high level of consistency from the age of approximately 3
years to 12 years, the pattern exhibited in children with autism is one of reduced consistency at 3 years with a slight increase at a later age, although not
approaching the level exhibited in the normal controls. In contrast, consistency
of hand preference in young children with learning disabilities begins at an
equivalent level to that of children with autism but appears to increase sharply,
so by 11 years it is approaching a level comparable with the normal children.
While these findings lend support to those reported by Satz and colleagues
(e.g., Satz et aL, 1988) who reported reduced consistency of hand preference,
referred to by them as ambiguous handedness (AH), in autistic populations
and mentally retarded populations compared to the incidence in the normal
population, the support is not unequivocal. According to Satz et al., AH may
indicate the presence of bilateral brain damage which has rendered neither
hemisphere capable of establishing motor dominance. They also postulate that
the overall level of intellectual functioning should be lower in comparison to
normal controls (although McManus et aL, 1992, found no evidence that AH
correlated with intelligence). To what extent Satz's theory is in accordance
with the present study is debatable. For instance, how can the theory account
for the increase in hand consistency found in the older autistic and learningdisabled group; it may simply be that the reduced hand preference consistency
of the younger autistic and learning-disabled children is the result of poor
motor functioning or delay in which practice with unimanual items will improve
consistency, although not to a level comparable to the normal population.
Hand Preference and Hand Skill
607
Skill-Preference Concordance. McManus et al. (1992) reported a dissociation of hand skill and hand preference in children with autism compared to children with learning disabilities and normal developing children,
who were matched for mental age. It must be remembered in interpreting
the present study that 52 of the 151 children for whom data are reported
are the same individuals as those of McManus et al. (1992), and in partitular they form all of the older autistic and older learning-disabled group.
Within the older group it is still clear that the autistic children have a higher
incidence of discordance than the learning-disabled and control groups, despite the control groups now being matched for chronological rather than
mental age. However the major discrepancy is in the younger children,
where there is no real evidence that any of the three groups matched for
chronological age differ in the extent of their concordance. Finally, it must
be noted that if the age groups are combined, although the differences
between groups do not reach statistical significance, the autistic group still
shows a higher incidence of discordance (37.1% of 35), compared with
18.0% of 89 normal developing controls, and 24.0% of 25 learning-disabled
controls; of course this trend might, in part, reflect that the overall group
still contains the same subjects as in the previous study of McManus et al.
Interpretation of these results is difficult. We have not carded out a strict
replication of the McManus et al. study, since the new subjects in the present study are much younger; and in that group there seems indeed to be
little evidence that children with autism differ from other children. It may
be that a proper replication of the McManus et al. study would indeed find
a similar effect; if so, then it will be necessary to develop a theoretical
model that can explain why discordance is present only in older children
with autism, as would seem to be the case here. Alternatively, the lack of
difference in the younger group may cast doubt on the phenomenon found
in the older group, implying that a proper replication would fail to find
differences similar to those found by McManus et al. (1992), and that their
result would then have to be construed as a Type I statistical error. Only
additional data can distinguish these two possibilities.
Conclusions
The present study has found a number of useful findings concerning the
nature of handedness in children with autism. In particular it shows that it is
possible to test children with autism in the age range 4-6 years and shows
dearly in that age range that the broad pattern of handedness is similar to
learning-disabled controls of similar chronological age, and that degree and
consistency of hand preference are both reduced substantially below normal
608
Cornish and McManus
developing controls of similar age. Of particular importance is that there are
no significant differences between autistic and learning-disabled children on
degree and consistency of hand preference, suggesting that these phenomena
are not specific to autism, but are a more general characteristic of children
with learning disabilities. However children with autism do differ from other
groups on the pegboard task, in particular although children with autism are
significantly impaired in comparison with age-matched normal controls at their
overall speed on the pegboard, they are nonetheless significantly faster than
learning-disabled controls; similar results apply for pegboard time with the
fight hand, with the left hand, with the better hand and with the worse hand,
but not for difference measures between the two hands. It is not clear why
this pattern of results should differentiate young children with autism from
other young children. Perhaps the most disappointing finding is the lack of a
difference between groups in the younger children in skill-preference concordance. As discussed earlier there are several interpretations of that finding.
Nevertheless it is clear that although in many ways children with autism are
similar to other children with learning disabilities, there is stillsuggestive evidence that children with autism show a distinctive and individual pattern of
handedness.
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