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F.-C. Chen et al.
arm configuration and make LT contact with the centre spot of
the touch plate (Fig. 2, right). Participants also had to maintain
the force exerted on the touch plate at less than 1 N (for detailed
touch force data, see Table I). If the peak contact force was greater
than the threshold value and/or apparent fingertip movement (i.e.
glide, roll, and spin) observed by an experimenter using a video
camera, the trial was stopped and repeated.
The sensitivity to LT test was also conducted at baseline (Test
1), between the NT and LT conditions (Test 2), and between
the NT/LT and LTAS conditions (Test 3). A previous study
demonstrated that immersing a finger in a 2% solution of so-
dium dodecyl sulphate can significantly increase touch-related
sensitivity (14). Thus, Test 3 was performed immediately after
finger soaking, in which participants immersed their dominant
index finger up to the proximal interphalangeal joint in a 2%
solution of sodium dodecyl sulphate (SDS 98%; Aldrich Che-
mical Company Inc., Milwaukee, WI, USA) for 5 min. The time
interval between blocks was 10 min, during which the children
remained seated to avoid fatigue. A complete experiment lasted
approximately 40–45 min for each participant.
and a lower value of this measure represents greater postural
stability and vice versa (24).
Group (2 levels: DCD and TDC) × Sensitivity Assessment (3
levels: Tests 1, 2 and 3) repeated-measure ANOVAs were used
to analyse sensitivity to LT. Group (2 levels: DCD and TDC) ×
Touch Condition (3 levels: NT, LT and LTAS) repeated-measure
ANOVAs were conducted for dominant upper limb movement
and body sway. A p-value < 0.05 was considered significant,
with Tukey post-hoc comparisons performed when necessary.
Estimates of effect sizes were made for significant main or
interaction effects using partial eta squared (η 2 ). All statistics
were calculated with SPSS 17.0 (SPSS Inc., Chicago, IL, USA).
RESULTS
Upper limb movement
No statistically significant effects on upper limb
movement were detected. Detailed descriptive and
inferential data are presented in Appendices 1 and 2.
Data analysis
A total sample size of 48 was used, with a power of 0.8 and
an α level of 0.05. There were 52 participants in this study (26
in the DCD group and 26 in the TDC group), such that the
actual power level was 0.84. Furthermore, the assumptions of
normality of variance were assessed and confirmed for all data
using Kolmogorov–Smirnov tests.
Statistical analysis
Movement of the dominant upper limb was represented by
mean displacement (in anterior-posterior (AP), medial-lateral
(ML) and vertical (VL) directions), as well as rotation (pitch,
roll and yaw) in the index finger, palm, forearm and upper
arm. Sensitivity to LT was measured in terms of individual
minimum detectable stimulus, expressed as a logarithm of 10
times the force in mg (23). The spatial amplitude of body sway
was quantified by the standard deviation of the COP trajectories
in the AP and ML axes. The standard deviation of the COP
trajectories was employed because it is a reliable measure (19)
Fig. 2. Experimental set-up.
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Sensitivity to light touch
Fig. 3 depicts sensitivity to LT (mean log of force) in
Tests 1, 2 and 3 for the children with DCD and TDC.
For the DCD group, the mean sensitivity to LT was 2.77
(standard deviation (SD) 0.29) in Test 1, 2.71 (SD 0.29)
in Test 2, and 2.38 (SD 0.33) in Test 3; for the TDC
group, sensitivity to LT was 2.46 (SD 0.28) in Test 1,
2.43 (SD 0.29) in Test 2, and 2.13 (SD 0.35) in Test 3.
The ANOVAs identified a main effect of Group (F(2,
50) = 26.64, p < 0.05, η 2 = 0.52), showing that children
with DCD had significantly greater sensitivity to LT
than did TDC. In addition, the results revealed a main
effect of Sensitivity Assessment (F(2, 50) = 18.85,
p < 0.05, η 2 = 0.27), showing that sensitivity to LT diffe-
red significantly among Tests 1, 2 and 3. Post-hoc tests
Fig. 3. Light touch sensitivity (mean log of force) in Tests 1, 2 and 3
for children with developmental coordination disorder (DCD) (black
triangles) and typically developing children (TDC) (grey squares). Bars
represent standard errors. Daggers denote a significant difference
between experimental conditions. Asterisks denote a significance
difference between children with DCD and TDC.