Research in Developmental Disabilities 35 (2014) 1237–1243
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Research in Developmental Disabilities
Sensorimotor function in preschool-aged children with expressive language disorder Iti Mu¨u¨rsepp *, Herje Aibast, Helena Gapeyeva, Mati Pa¨a¨suke University of Tartu, Institute of Exercise Biology and Physiotherapy, Ujula 4, 51008 Tartu, Estonia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 29 November 2013 Received in revised form 7 March 2014 Accepted 7 March 2014 Available online 28 March 2014
Aim: The aim of the study was to evaluate functional motor performance and haptic object recognition in 5-year-old children with mild expressive language disorder (ELD) in comparison with age- and gender-matched healthy children. Methods: The subjects were classified by speech-language pathologist using The Reynell Developmental Language Scales III and Boehm Test of Basic Concepts: Preschool as children with mild ELD (n = 29, incl. 23 boys and 6 girls) and children with typical language development as controls (n = 29, incl. 23 boys and 6 girls). The children were examined for manual dexterity, ball skills, static and dynamic balance by Movement-ABC, haptic object recognition (HOR), hand-grip strength (HGS) and vertical jumping performance. Results: Children with mild ELD demonstrated significantly higher scores (i.e., inferior performance) in all subtests of M-ABC (all p values 0.05) emerged from HGS. Boys with mild ELD demonstrated higher results in impairment score (p < 0.001), ball skills (p < 0.01) and balance (p < 0.01) of M-ABC, as well as in HOR (p < 0.05). Girls with mild ELD showed higher impairment score (p < 0.05) with lower percentile (p < 0.05) in M-ABC, indicating inferior motor performance, and lower HGS for the non-dominant hand (p < 0.05). Seven out of 29 (24.1%) children with mild ELD had definite or borderline motor difficulties, while only one child in control group (3.4%) demonstrated borderline motor difficulties. Conclusions: Children with mild expressive language disorder do not perform as well as controls in tests of functional motor skills, but their results in tests demanding maximal muscle force generation are in level with typically developing children. Boys and girls with mild ELD demonstrated higher impairment scores in M-ABC, indicating the need to follow their overall development more closely. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Motor skills Motor performance Specific language impairment Perception Muscle strength
1. Introduction Specific language impairment (SLI), also known as developmental speech and language disorder (DSLD), occurs in 6.3% of children with the male rate approximately double in comparison of female rate (Pinborough-Zimmerman et al., 2007). SLI involves delays or deficits in expressive or receptive language development, or both, in the absence of observed mental
* Corresponding author. Tel.: +372 737 6286; fax: +372 737 6286. E-mail addresses: [email protected] (I. Mu¨u¨rsepp), [email protected] (H. Aibast), [email protected] (H. Gapeyeva), [email protected] (M. Pa¨a¨suke). http://dx.doi.org/10.1016/j.ridd.2014.03.007 0891-4222/ß 2014 Elsevier Ltd. All rights reserved.
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retardation, hearing loss, environmental deprivation or neurological disorders (Leonard, 1998; Tomblin et al., 1997). In case of isolated expressive language disorder (ELD) children may have small vocabularies; they use short, incomplete sentences and produce confusing or disorganized conversations (Johnson, 2007). Girls predominate in expressive–receptive problems, while boys predominate in expressive language and oral-motor problems (Selassie, Jennische, Kyllerman, Viggedal, & Hartelius, 2005). There is a considerable evidence suggesting that children with SLI experience varying degrees of fine (e.g., cutting with scissors, peg moving, bead threading, finger tapping) and gross motor (e.g., toe gate, walking in a straight line, static balance, hopping, jumping forward on both feet) deficit (Finlay & McPhillips, 2013; Iverson & Braddock, 2011; Rechetnikov & Maitra, 2009; Visscher, Houwen, Scherder, Moolenaar, & Hartman, 2007; Vukovic, Vukovic, & Stojanovik, 2010; Webster et al., 2006). According to different authors the prevalence of motor dysfunction in children with SLI varies from about 34 to 90% (Pieters et al., 2012; Rechetnikov & Maitra, 2009). Vukovic et al. (2010) discovered that children with SLI are delayed in the development of motor skills requiring coordination of legs and arms, as well as the ability to imitate movements. Also Hill (2001) interpreted the lower motor and language skills in children with SLI as an underlying neurological immaturity. Although force-generation capacity of skeletal muscles is an important indicator of neuromuscular functioning and it is essential for performing different daily activities (Damiano & Abel, 1996), previous studies have dealt this area only briefly. It has been shown that the hand-grip strength and muscle strength of leg extensors in boys with ELD is weaker compared to typically developing boys (Mu¨u¨rsepp, Aibast, & Pa¨a¨suke, 2011). Data considering the maximal voluntary muscle strength in girls with ELD is insufficient. Visscher et al. (2010) discovered in their study about distinguishing the existence of motor impairments between schoolaged boys and girls with DSLD, that object control skill deficiencies were more extensive for girls than boys (Visscher et al., 2010). They also showed that children with language disorders performed better in object control tasks than children with speech disorders (Visscher et al., 2010) and children with receptive disorders have better motor performance than children with combined expressive and receptive language disorders (Visscher et al., 2007). Researches have also shown that SLI is often accompanied by non-linguistic cognitive deficits, including perceptual deficit (Ullman & Pierpont, 2005). Haptic perception is a complex ability requiring adequate cutaneous and kinaesthetic information, hand-movement patterns and cross-modal haptico-visual transfer (Bushnell & Baxt, 1999; Lederman & Klatzky, 1998). The study of Montgomery (1993) reported that children with SLI perform more poorly in HOR tasks than their typically developing peers. Data of our pervious study (Mu¨u¨rsepp, Aibast, Gapeyeva, & Pa¨a¨suke, 2012) revealed that the haptic perception in children with mild ELD is considerably more affected than in children with articulation disorder compared to controls. Unfortunately, data about haptic perception in children with SLI is still insufficient especially concerning differences between genders or specific types of SLI. The majority of previous studies have recruited children with DSLD from clinics or special schools (Finlay & McPhillips, 2013; Iverson & Braddock, 2011; Visscher et al., 2007; Vukovic et al., 2010; Webster et al., 2006), but their impairment severity or type of dysfunction has in most cases remained unspecified. On the other hand, it has been shown that motor function impairment correlates strongly with the observed severity of the child’s language disorder (Webster et al., 2006), e.g., the more severe is language disorder, the more pronounced is motor deficit. Nevertheless, it is still very little known how mild ELD can affect functional motor performance and perception of preschool-aged boys and girls. The purpose of this study was to examine functional sensorimotor abilities in children with mild ELD compared to typically developing children. Furthermore, as previous studies have not distinguished subjects by gender, the present study identified the existence of sensorimotor dysfunction separately in groups of boys and in groups of girls. 2. Materials and methods 2.1. Participants The participants were recruited from 7 ordinary kindergartens of Tartu, Estonia. Organizers of the study excluded the recruitment of children from special squads or kindergartens for children with severe speech and language disorders or problems in mental or physical development. Speech and language therapists working at the kindergartens were asked to provide a sample of children with language impairment from their workload. The speech therapists produced a list of 62 children aged 5–6 years who had expressive oral language problems. All these 62 children underwent assessment of language skills by The Reynell Developmental Language Scales III (Edwards et al., 1997) and Boehm Test of Basic Concepts: Preschool (Boehm, 2008) administered by professional speech-language pathologists from the University Clinic of Tartu. A deviation of 1 SD below the age standards in language tests was used as cut-off for mild speech-language impairments. Of the 62 children, 6 children (5 boys and 1 girl) were excluded because they scored below 1.5 SD in language tests, referring to moderate speech-language impairments and 27 children (20 boys and 7 girls) were excluded because of the occurrence of oral motor problems only. There were no children with combined type (receptive– expressive) language disorder. Control group (CG) children were randomly selected from the same kindergartens and matched according to age- and sex (23 boys and 6 girls). These 29 CG children also went through language assessments to confirm typical language development. All 58 children included in our study were confirmed to be developing
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Table 1 Mean (SE) age and results of Reynell Developmental Language Scales III (RDLS) and Boehm Test of Basic Concepts: Preschool (Boehm-3) in children with mild expressive language disorder (ELD) and in control group (CG) children. Parameters
ELD children n = 29
CG children n = 29
ELD boys n = 23
CG boys n = 23
ELD girls n=6
CG girls n=6
Age (months)
65.9.0 0.8 p = 0.752 54.7 0.3yyy p = 0.000 81.4 1.4yyy p = 0.000
66.2 0.7
66.2 0.9 p = 0.918 54.7 0.3bbb p = 0.000 82.0 1.5bbb p = 0.000
66.3 0.9
64.8 1.7 p = 0.609 55.0 0.4*** p = 0.000 79.3 3.6** p = 0.003
66.0 1.4
RDLS (points) Boehm-3: correct answers (%)
58.4 0.3 92.3 1.0
58.1 0.4 91.7 1.0
59.5 0.6 95.0 2.0
yyy
p < 0.001 compared to CG children. p < 0.001 compared to CG boys. ** p < 0.01 compared to CG girls. *** p < 0.001 compared to CG girls.
bbb
adequately (except in the area of speech and language in children with ELD) by kindergarten paediatricians, who regularly assess children for different developmental aspects. All children with ELD were able to learn on the same level as their peers. All motor performance and haptic object recognition assessments were performed individually by appropriately qualified therapists who were blinded to the child’s group assignment. Mean age of the participants and results of the language tests are presented in Table 1. The parents gave informed consent for their children’s participation. Approval for this study was given by the Ethics Committee, University of Tartu. 2.2. Functional motor performance Functional motor performance was measured by the Movement Assessment Battery for Children (M-ABC) (Henderson & Sugden, 1992). This test battery consists of 3 subtests: manual dexterity, ball skills, and static and dynamic balance. Each item is scored on a scale from 0 to 5: score 0 is obtained for faultless performance, score 5 in case of failure. Summing the item scores of the 3 subtests generates an age-standardized impairment score (IS) from which a child’s percentile can be calculated. High IS and low percentile indicate poor motor performance. Children scoring below the 5th percentile on the MABC were considered to have definite motor impairment, whereas children scoring between 5th and 15th percentile were considered to have borderline motor difficulties. 2.3. Haptic object recognition A bag with 5 common objects of daily living (key, toothbrush, teaspoon, pencil, clothes-peg) was used to measure haptic perception. The subjects were not familiar with the content of the bag. The child was instructed to put his hand into the bag, take one item at a time, feel it, and guess what it is without visual stimuli. After answering the subject was allowed to take a look at the item. If the child gave the correct answer within 5 s, he was scored 0 and if he gave the answer after 5 s, he was scored 1. The child was scored 2 when he gave at first the wrong answer but corrected himself within 3 s; and 3 if he gave the wrong answer without correction. To eliminate the influence of vocabulary deficiencies, the examiner instructed subjects to either name the item or say what it is used for. If the child could not name the item but said what he can use it for, or when the answer was not grammatically accurate but comprehensible, it was counted correct. Summing the scores for recognizing 5 items formed the total score. Higher scores indicated poorer haptic object recognition ability. 2.4. Hand-grip strength Maximal isometric hand-grip strength of the dominant (HGSD) and non-dominant (HGSND) hand was determined with standard mechanical hand-dynamometer (Lafayette, USA). The test was performed in standing position, hand held unbent on the side. The subjects were instructed to squeeze the handle as forcefully as possible for 2–3 s. Three maximal efforts with both hands were performed and the value of the strongest squeeze was recorded as maximal isometric hand-grip strength. A rest period of 2 min was allowed between the squeezes. 2.5. Vertical jumping performance The vertical jumping test was performed on a force platform (Kistler 9286A, Switzerland) with the dimensions of 0.40 m 0.60 m and natural frequency of 500 Hz. The subjects were instructed to jump as high as possible with preliminary
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counter movement with their hands on the hips. The following characteristics were recorded by a vertical force–time curve for each jump: (1) Jumping height (VJH) by the height of the body centre of gravity: VJH ¼
gt2f 8
;
where g is acceleration of gravity (9.81 m/s2) and tf flight time. (2) Peak vertical ground reaction force (VJGRF). Each subject performed three maximal jumps and the highest jump was used for further analysis. A rest period of 2 min was allowed between the jumps. 2.6. Data analysis Statistical analysis was performed by using SPSS 18 software. Comparative analysis between children with mild ELD and controls was done by using one-way ANOVA followed by Bonferroni post hoc test for normally distributed data (age, scores of RDLS, Boehm-3, HGS and VJ) and the Mann–Whitney U tests (scores of MABC and HOR) for not normally distributed data. A level of p < 0.05 was selected to indicate statistical significance. 3. Results 3.1. Functional motor performance Table 2 displays the mean values of M-ABC results for IS, percentile, manual dexterity, ball skills and balance of both groups. Comparison of groups revealed significant differences for the impairment score (p = 0.000), percentile (p = 0.000), manual dexterity (p = 0.048), ball skills (p = 0.003) and balance (p = 0.001): children with mild ELD performed at considerably lower level in functional motor tests. Two children (1 boy and 1 girl; 6.9%) in ELD group achieved scores below 5th percentile suggesting a significant level of motor impairment. Five children (3 boys and 2 girls; 17.2%) in ELD group and one boy (3.4%) in CG scored between 5th and 15th percentile, showing a moderate level of motor problems. Boys with mild ELD had significantly higher (p = 0.001) impairment score and lower percentile (p = 0.002) compared to CG boys indicating less efficient motor performance, that was more pronounced in subtests of ball skills (p = 0.006) and balance (p = 0.009). For girls with mild ELD statistically relevant differences in M-ABC scores emerged from impairment score (p = 0.020) and percentile (p = 0.020), indicating inferior motor performance compared to CG girls.
Table 2 Mean (SE) values of M-ABC impairment score (IS), percentile and subtests; haptic object recognition (HOR) score and percentage of answers given with latency (HOR: late answers) in children with mild expressive language disorder (ELD) and in control group (CG) children. Parameters
ELD children n = 29
CG children n = 29
IS (points)
7.2 1.1yyy p = 0.000 38.3 5.2yyy p = 0.000 1.9 0.5y p = 0.048 2.7 0.5yy p = 0.003 2.5 0.5yyy p = 0.001 4.7 0.6yy p = 0.010 17.9 3.9 p = 0.619
2.1 0.6
Percentile Manual dext. (points) Ball skills (points) Balance (points) HOR (points) HOR: late answers (%) y
p < 0.05 compared to CG children. p < 0.01 compared to CG children. p < 0.001 compared to CG children. b p < 0.05 compared to CG boys. bb p < 0.01 compared to CG boys. bbb p < 0.001 compared to CG boys. * p < 0.051 compared to CG girls. ** p < 0.01 compared to CG girls. yy
yyy
72.8 4.7 0.7 0.2 0.9 0.3 0.5 0.2 2.6 0.4 15.2 3.5
ELD boys n = 23 6.1 1.0bbb p = 0.001 41.6 6.0bb p = 0.002 1.4 0.4 p = 0.236 2.5 0.5bb p = 0.006 2.2 0.5bb p = 0.009 4.8 0.7b p = 0.026 13.0 3.7 p = 0.398
CG boys n = 23
ELD girls n=6
CG girls n=6
72.3 10.2
0.7 0.3
11.1 3.9* p = 0.020 25.8 8.4* p = 0.020 3.8 1.5 p = 0.066
0.7 0.4
3.5 1.5 p = 0.423
1.3 0.6
0.6 0.3
3.8 1.6 p = 0.093
0.2 0.1
2.6 0.4
4.2 0.7 p = 0.423
2.8 1.0
36.7 9.5** p = 0.010
3.3 3.3
2.1 0.7 72.9 5.5
18.3 4.2
1.9 1.0
0.4 0.3
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Table 3 Mean (SE) values of maximal isometric hand-grip strength of the dominant (HGSD) and non-dominant (HGSND) hand, vertical jumping height (VJH) and peak vertical ground reaction force (VJGRF) in children with mild expressive language disorder (ELD) and in control group (CG) children. Parameters
ELD children n = 29
CG children n = 29
HGSD (N)
10.2 0.5 p = 0.199 9.9 0.6 p = 0.073 0.13 0.01y p = 0.028 253.0 14.8 p = 0.062
11.1 0.3
HGSND (N) VJH (cm) VJGRF (N)
10.4 0.4 0.15 0.01 218.7 10.1
ELD boys n = 23 10.6 0.6 p = 0.610 10.4 0.6 p = 0.978 0.13 0.01 p = 0.335 260.3 16.9b p = 0.042
CG boys n = 23 10.9 0.4 10.4 0.4 0.15 0.01 219.1 10.1
ELD girls n=6 9.0 0.9 p = 0.056 7.9 0.9* p = 0.032 0.14 0.01 p = 0.096 225.0 30.3 p = 0.867
CG girls n=6 11.5 0.7 10.7 0.6 0.17 0.01 217.3 32.7
y
p < 0.05 compared to CG children. p < 0.05 compared to CG boys. * p < 0.05 compared to CG girls.
b
3.2. Haptic object recognition Children with mild ELD had significantly more difficulties (p = 0.01) in HOR test compared to controls (Table 2). Boys with ELD made considerably more errors (p = 0.026) in HOR task than the boys of CG. Although the girls with mild ELD recognized objects haptically in the same level (p = 0.423) as CG girls, they gave significantly more (p = 0.01) answers with latency (>5 s). 3.3. Hand-grip strength The mean values of maximal isometric HGS of both groups are presented in Table 3. No significant differences in HGSD and HGSND were observed between children with mild ELD and CG, F(1, 56) = 1.69, p = 0.199 and F(1, 56) = 3.33, p = 0.073 respectively; as well as between boys with ELD and CG boys, F(1, 44) = 0.26, p = 0.61 and F(1, 44) = 0.001, p = 0.978 respectively. The maximal isometric HGSD of girls with mild ELD did not differ considerably from the same parameter of CG girls, F(1, 10) = 4.69, p = 0.056; but their HGSND was significantly weaker compared to CG girls, F(1, 10) = 6.21, p = 0.032. 3.4. Vertical jumping performance The mean values of vertical jumping performance for the measured groups are displayed in Table 3. VJH of children with mild ELD was lower compared to CG children, F(1, 56) = 5.11, p = 0.028; although there were no statistically significant differences in peak vertical ground reaction force between the groups, F(1, 56) = 3.63, p = 0.062. Boys with mild ELD demonstrated greater VJGRF, F(1, 44) = 4.37, p = 0.042; but statistically equal VJH compared to CG boys, F(1, 44) = 0.95, p = 0.335. The differences in VJH and VJGRF were insignificant between girls with ELD and CG girls, F(1, 10) = 3.39, p = 0.096 and F(1, 10) = 0.03, p = 0.867 respectively. 4. Discussion This research studied motor performance and haptic object recognition ability of children with mild specific expressive language impairment in preschool-age. All these children received speech therapy, but no extra educational assistance and were placed within an ordinary kindergartens. The main findings of this research were: (1) children with mild ELD demonstrated lower level functional motor skills compared to control group; (2) muscle force generation capacity of children with mild ELD is less affected; (3) although there were no statistically significant differences in functional motor abilities of girls with mild ELD, their test scores indicated less efficient motor performance compared to CG girls. The scores of Movement Assessment Battery for Children demonstrated that general functional motor performance of children with mild ELD was less efficient than typically developing children’s in all subtests, as well as expressed by impairment score and percentile. Boys with mild ELD obtained markedly higher scores in ball skills and balance subtests but not in manual dexterity task compared to CG boys. There were no significant differences in manual dexterity, ball skills or balance of girls with mild ELD compared to CG girls. However, their test scores were much higher, especially in subtests of manual dexterity and balance, compared to the same scores of typically developing girls. These results are in accordance with the previous studies (Finlay & McPhillips, 2013; Rechetnikov & Maitra, 2009; Visscher et al., 2007; Webster et al., 2006) where children with DSLD demonstrated deficit in overall M-ABC results. Our results also confirm the conclusion of Visscher et al. (2007), who pointed out that the children with speech disorders perform poorer in the tests of ball skills and static balance. On the other hand, data of our research is only partly in line with the study results of Estil, Whiting, Sigmundsson, and Ingvaldsen (2003), which showed especially poor bimanual coordination of children with SLI. In our study the differences in manual dexterity between the groups of children were not so pronounced and were not statistically relevant when comparing separately the groups of boys and girls. It has to be stressed that the above mentioned studies observed mostly children with moderate or severe speech and language disorders from special schools. Our data revealed lower level
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functional motor abilities also in children with only mild ELD. It has been shown (Selassie et al., 2005) that girls predominate in combined expressive–receptive language problems that affect motor performance more seriously than isolated expressive or receptive problems. In our study there were no children with combined language problems. Although we could not reveal statistically relevant differences in motor performance between groups of girls, there was a tendency for girls with mild ELD to perform less efficiently compared to CG girls in functional motor tests. The absence of statistically relevant differences could be due to small number of girls participating in our study that could mask the real outcome of the assessment. It has been found that important brain structures involved in speech and language production, as well as in sequencing, speed, ball skills and balance control are cerebellum and basal ganglia (Fawcett & Nicolson, 1999; Timmann, Watts, & Hore, 1999; Ullman & Pierpont, 2005). Considering the theories of slower neurodevelopment of children with SLI (Hill, 2001; Vukovic et al., 2010), it can be suggested that the less efficient functional motor performance of children with mild ELD could be elucidated by the immaturity of these brain structures. Further research with larger groups of girls is necessary to confirm the findings of this study as well as to detect the underlying mechanism of ELD. In the haptic object-recognition task children with mild ELD made considerably more errors than controls. Further analysis revealed that boys with ELD had substantially more difficulties with haptic object recognition compared to the same-age counterparts. The girls with mild ELD made also more mistakes in HOR task compared to the girls of CG, although these were not reaching the statistical significance. Considerable difference emerged only in timing parameter of HOR test: girls with mild ELD needed significantly more seconds (>5 s) to give the right answer. These results partly confirmed previous notions (Giannopulu, Cusin, Escolano, & Dellatolas, 2008) that children with DSLD have lower ability to recognize common objects haptically. However, several researchers (Kiesel-Himmel, 2008; Montgomery, 1993) have emphasized that children with DSLD are not deficient in their proprioceptive abilities but they might have problems with performing adequate hand movement patterns or with complex cognitive capabilities like tactile short term memory and cross-modal transfer. The motor coordination of complex movements during haptic object recognition are claimed to be mainly dependent on the posterior cerebellum (Habas & Cabanis, 2008) and the sensorimotor sequences of skill performance on the basal ganglia (Ullman & Pierpont, 2005). Considering the assumption of immature neurodevelopment in children with ELD, inferior haptic performance refers most likely to their inability to select and/or perform appropriate hand movement patterns. As the differences in average subtest score of manual dexterity for children with ELD compared to CG children was not considerable, the difficulties in haptic object-recognition are probably not caused by improper processing of kinaesthetic inputs or by detriment of involved brain structures. Our study demonstrated that maximal force generation capacity in isometric hand-grip strength was statistically on the same level for children with mild ELD and controls. The HGS for both hands of boys with ELD was almost equal to CG boys, which confirms the results of M-ABC about adequate hand function. The hand-grip strength of the non-dominant hand of girls with mild ELD was noticeably weaker than of CG girls. There was also a tendency for weaker HGS of the dominant hand that did not reach statistical relevance. There are few studies (Mu¨u¨rsepp et al., 2011) where force generation capacity of children with SLI has been researched. In the mentioned study, the boys with mild to moderate ELD demonstrated lower maximal voluntary contraction force of the leg extensor muscles. Data of the present study confirmed statistical differences in maximal hand-grip strength only in case of the non-dominant hand of girls with mild ELD. As several central (neural) and peripheral (muscular) factors can determine the differences in muscle voluntary force-generating capacity, one possible explanation may be less developed central processing mechanisms in the hemisphere and cerebellum during voluntary effort of girls with ELD. Interestingly, Estil et al. (2003) pointed out that children with SLI demonstrate poor performance in the static balance test especially with the left leg. Further research is necessary to explain the background and extent of these dysfunctions of girls with mild ELD. Vertical jumps can be used as a model to study explosive force-generating capacity of the lower extremities and ability to coordinate movements of different body parts. The results of this study showed lower vertical jumping height demonstrated by children with mild ELD compared to controls. However, the differences between the boys with ELD and CG boys as well as between girls with ELD and CG girls were not statistically significant. Children with mild ELD demonstrated somewhat higher peak vertical ground reaction force compared to controls, but only the difference between the groups of boys was statistically relevant. Vertical jumping is a multi-joint movement and requires the intra- and intermuscular coordination, which describes the ability of agonists, antagonists and synergists to co-operate in performing the task. This ability depends on the sufficient maturity of nervous system. A few earlier investigators (Merriman, Barnett, & Kofka, 1993; Owen & McKinlay, 1997) have shown the less developed motor coordination in children with SLI compared with typically developing children. Our research results are in accordance with the study of Merriman et al. (1993), showing that peak force of children with SLI is not lower compared to control group children. In the mentioned study, differences emerged only from the components of jumping movement. The lower jumping height of children with mild ELD in the present study is most probably the consequence of deficient ability to coordinate one’s leg extensor muscles. Relatively higher production of peak vertical ground reaction force of the boys and girls with mild ELD compared to controls confirms this theory. This study shows that children even with mild expressive language disorder perform at lower level compared to controls in tests of functional motor skills, but not in tests demanding muscle force generation capacity. The motor proficiency of boys with mild ELD is clearly affected compared to the same-aged peers. The girls with mild ELD also demonstrate the tendency to have more difficulties in functional motor tasks. From a clinical perspective, a broader assessment procedure for children at
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risk of language disorders should be admitted to detect multiple deficits and encourage a wider range of intervention strategies. Although this study has added value to our understanding of the motor performance of boys and girls with mild expressive language disorder, it does not solve the current debate about the underlying nature of SLI. The sample sizes were relatively small, especially for the group of girls, and the findings merit replication with larger number of participants. References Boehm, A. E. (2008). Boehm test of basic concepts: Technical report. Pearson Education Inc.. Retrieved from http://www.pearsonassessments.com/NR/rdonlyres/ AD66E61D-466B-406F-812F-BC6F1C120B17/0/Boehm_PS_TR_Web.pdf. Bushnell, E. W., & Baxt, C. (1999). Children’s haptic and cross-modal recognition with familiar and unfamiliar objects. Journal of Experimental Psychology: Human Perception and Performance, 25(6), 1867–1881. Damiano, D. L., & Abel, M. F. (1996). 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Retrieved from http://www.literacyencyclopedia.ca/pdfs/Prevalence_of_Speech_and_Language_Disorders_in_Children.pdf. Kiesel-Himmel, C. (2008). Haptic perception in infancy and first acquisition of object words: Developmental and clinical approach. In M. Gru¨nwald (Ed.), Human haptic perception: Basics and applications. Basel: Birkha¨user Verlag. Lederman, S. J., & Klatzky, R. L. (1998). The hand as a perceptual system. In K. Connolly (Ed.), The psychobiology of the hand (pp. 16–35). London: MacKeith Press. Leonard, L. B. (1998). Children with specific language impairment. Cambridge, MA: MIT Press. Merriman, W. J., Barnett, B. E., & Kofka, J. B. (1993). The standing long jump performances of preschool children with speech impairments and children with normal speech. Adapted Physical Activity Quarterly, 10, 157–163. Montgomery, J. W. (1993). Haptic recognition of children with specific language impairment: Effects of response modality. Journal of Speech and Hearing Research, 36, 98–104. Mu¨u¨rsepp, I., Aibast, H., & Pa¨a¨suke, M. (2011). Motor performance and haptic perception in preschool boys with specific impairment of expressive language. Acta Paediatrica, 100(7), 1038–1042. Mu¨u¨rsepp, I., Aibast, H., Gapeyeva, H., & Pa¨a¨suke, M. (2012). Motor skills, haptic perception and social abilities in children with mild speech disorders. Brain and Development, 34(2), 128–132. Owen, S. E., & McKinlay, I. A. (1997). Motor difficulties in children with developmental disorders of speech and language. Child: Care, Health and Development, 23(4), 315–325. Pieters, S., De Block, K., Scheiris, J., Eyssen, M., Desoete, A., Deboutte, D., et al. (2012). How common are motor problems in children with a developmental disorder: Rule or exception? Child: Care, Health and Development, 38(1), 139–145. Pinborough-Zimmerman, J., Satterfield, R., Miller, J., Bilder, D., Hossain, S., & McMahon, W. (2007). Communication disorders: Prevalence and comorbid intellectual disability, autism, and emotional/behavioral disorders. American Journal of Speech-Language Pathology, 16(4), 359–367. Rechetnikov, R. P., & Maitra, K. (2009). Motor impairments in children associated with impairments of speech or language: A meta-analytic review of research literature. American Journal of Occupational Therapy, 63, 255–263. Selassie, G. R., Jennische, M., Kyllerman, M., Viggedal, G., & Hartelius, L. (2005). Comorbidity in severe developmental language disorders: Neuropediatric and psychological considerations. Acta Paediatrica, 94, 471–478. Timmann, D., Watts, S., & Hore, J. (1999). Failure of cerebellar patients to time finger opening precisely causes ball high-low inaccuracy in overarm throws. Journal of Neurophysiology, 82, 103–114. Tomblin, J. B., Records, N. L., Buckwalter, P., Zhang, X., Smith, E., & O’Brien, M. (1997). Prevalence of specific language impairment in kindergarten children. 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Contents lists available at ScienceDirect
Research in Developmental Disabilities
Sensorimotor function in preschool-aged children with expressive language disorder Iti Mu¨u¨rsepp *, Herje Aibast, Helena Gapeyeva, Mati Pa¨a¨suke University of Tartu, Institute of Exercise Biology and Physiotherapy, Ujula 4, 51008 Tartu, Estonia
A R T I C L E I N F O
A B S T R A C T
Article history: Received 29 November 2013 Received in revised form 7 March 2014 Accepted 7 March 2014 Available online 28 March 2014
Aim: The aim of the study was to evaluate functional motor performance and haptic object recognition in 5-year-old children with mild expressive language disorder (ELD) in comparison with age- and gender-matched healthy children. Methods: The subjects were classified by speech-language pathologist using The Reynell Developmental Language Scales III and Boehm Test of Basic Concepts: Preschool as children with mild ELD (n = 29, incl. 23 boys and 6 girls) and children with typical language development as controls (n = 29, incl. 23 boys and 6 girls). The children were examined for manual dexterity, ball skills, static and dynamic balance by Movement-ABC, haptic object recognition (HOR), hand-grip strength (HGS) and vertical jumping performance. Results: Children with mild ELD demonstrated significantly higher scores (i.e., inferior performance) in all subtests of M-ABC (all p values 0.05) emerged from HGS. Boys with mild ELD demonstrated higher results in impairment score (p < 0.001), ball skills (p < 0.01) and balance (p < 0.01) of M-ABC, as well as in HOR (p < 0.05). Girls with mild ELD showed higher impairment score (p < 0.05) with lower percentile (p < 0.05) in M-ABC, indicating inferior motor performance, and lower HGS for the non-dominant hand (p < 0.05). Seven out of 29 (24.1%) children with mild ELD had definite or borderline motor difficulties, while only one child in control group (3.4%) demonstrated borderline motor difficulties. Conclusions: Children with mild expressive language disorder do not perform as well as controls in tests of functional motor skills, but their results in tests demanding maximal muscle force generation are in level with typically developing children. Boys and girls with mild ELD demonstrated higher impairment scores in M-ABC, indicating the need to follow their overall development more closely. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Motor skills Motor performance Specific language impairment Perception Muscle strength
1. Introduction Specific language impairment (SLI), also known as developmental speech and language disorder (DSLD), occurs in 6.3% of children with the male rate approximately double in comparison of female rate (Pinborough-Zimmerman et al., 2007). SLI involves delays or deficits in expressive or receptive language development, or both, in the absence of observed mental
* Corresponding author. Tel.: +372 737 6286; fax: +372 737 6286. E-mail addresses: [email protected] (I. Mu¨u¨rsepp), [email protected] (H. Aibast), [email protected] (H. Gapeyeva), [email protected] (M. Pa¨a¨suke). http://dx.doi.org/10.1016/j.ridd.2014.03.007 0891-4222/ß 2014 Elsevier Ltd. All rights reserved.
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retardation, hearing loss, environmental deprivation or neurological disorders (Leonard, 1998; Tomblin et al., 1997). In case of isolated expressive language disorder (ELD) children may have small vocabularies; they use short, incomplete sentences and produce confusing or disorganized conversations (Johnson, 2007). Girls predominate in expressive–receptive problems, while boys predominate in expressive language and oral-motor problems (Selassie, Jennische, Kyllerman, Viggedal, & Hartelius, 2005). There is a considerable evidence suggesting that children with SLI experience varying degrees of fine (e.g., cutting with scissors, peg moving, bead threading, finger tapping) and gross motor (e.g., toe gate, walking in a straight line, static balance, hopping, jumping forward on both feet) deficit (Finlay & McPhillips, 2013; Iverson & Braddock, 2011; Rechetnikov & Maitra, 2009; Visscher, Houwen, Scherder, Moolenaar, & Hartman, 2007; Vukovic, Vukovic, & Stojanovik, 2010; Webster et al., 2006). According to different authors the prevalence of motor dysfunction in children with SLI varies from about 34 to 90% (Pieters et al., 2012; Rechetnikov & Maitra, 2009). Vukovic et al. (2010) discovered that children with SLI are delayed in the development of motor skills requiring coordination of legs and arms, as well as the ability to imitate movements. Also Hill (2001) interpreted the lower motor and language skills in children with SLI as an underlying neurological immaturity. Although force-generation capacity of skeletal muscles is an important indicator of neuromuscular functioning and it is essential for performing different daily activities (Damiano & Abel, 1996), previous studies have dealt this area only briefly. It has been shown that the hand-grip strength and muscle strength of leg extensors in boys with ELD is weaker compared to typically developing boys (Mu¨u¨rsepp, Aibast, & Pa¨a¨suke, 2011). Data considering the maximal voluntary muscle strength in girls with ELD is insufficient. Visscher et al. (2010) discovered in their study about distinguishing the existence of motor impairments between schoolaged boys and girls with DSLD, that object control skill deficiencies were more extensive for girls than boys (Visscher et al., 2010). They also showed that children with language disorders performed better in object control tasks than children with speech disorders (Visscher et al., 2010) and children with receptive disorders have better motor performance than children with combined expressive and receptive language disorders (Visscher et al., 2007). Researches have also shown that SLI is often accompanied by non-linguistic cognitive deficits, including perceptual deficit (Ullman & Pierpont, 2005). Haptic perception is a complex ability requiring adequate cutaneous and kinaesthetic information, hand-movement patterns and cross-modal haptico-visual transfer (Bushnell & Baxt, 1999; Lederman & Klatzky, 1998). The study of Montgomery (1993) reported that children with SLI perform more poorly in HOR tasks than their typically developing peers. Data of our pervious study (Mu¨u¨rsepp, Aibast, Gapeyeva, & Pa¨a¨suke, 2012) revealed that the haptic perception in children with mild ELD is considerably more affected than in children with articulation disorder compared to controls. Unfortunately, data about haptic perception in children with SLI is still insufficient especially concerning differences between genders or specific types of SLI. The majority of previous studies have recruited children with DSLD from clinics or special schools (Finlay & McPhillips, 2013; Iverson & Braddock, 2011; Visscher et al., 2007; Vukovic et al., 2010; Webster et al., 2006), but their impairment severity or type of dysfunction has in most cases remained unspecified. On the other hand, it has been shown that motor function impairment correlates strongly with the observed severity of the child’s language disorder (Webster et al., 2006), e.g., the more severe is language disorder, the more pronounced is motor deficit. Nevertheless, it is still very little known how mild ELD can affect functional motor performance and perception of preschool-aged boys and girls. The purpose of this study was to examine functional sensorimotor abilities in children with mild ELD compared to typically developing children. Furthermore, as previous studies have not distinguished subjects by gender, the present study identified the existence of sensorimotor dysfunction separately in groups of boys and in groups of girls. 2. Materials and methods 2.1. Participants The participants were recruited from 7 ordinary kindergartens of Tartu, Estonia. Organizers of the study excluded the recruitment of children from special squads or kindergartens for children with severe speech and language disorders or problems in mental or physical development. Speech and language therapists working at the kindergartens were asked to provide a sample of children with language impairment from their workload. The speech therapists produced a list of 62 children aged 5–6 years who had expressive oral language problems. All these 62 children underwent assessment of language skills by The Reynell Developmental Language Scales III (Edwards et al., 1997) and Boehm Test of Basic Concepts: Preschool (Boehm, 2008) administered by professional speech-language pathologists from the University Clinic of Tartu. A deviation of 1 SD below the age standards in language tests was used as cut-off for mild speech-language impairments. Of the 62 children, 6 children (5 boys and 1 girl) were excluded because they scored below 1.5 SD in language tests, referring to moderate speech-language impairments and 27 children (20 boys and 7 girls) were excluded because of the occurrence of oral motor problems only. There were no children with combined type (receptive– expressive) language disorder. Control group (CG) children were randomly selected from the same kindergartens and matched according to age- and sex (23 boys and 6 girls). These 29 CG children also went through language assessments to confirm typical language development. All 58 children included in our study were confirmed to be developing
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Table 1 Mean (SE) age and results of Reynell Developmental Language Scales III (RDLS) and Boehm Test of Basic Concepts: Preschool (Boehm-3) in children with mild expressive language disorder (ELD) and in control group (CG) children. Parameters
ELD children n = 29
CG children n = 29
ELD boys n = 23
CG boys n = 23
ELD girls n=6
CG girls n=6
Age (months)
65.9.0 0.8 p = 0.752 54.7 0.3yyy p = 0.000 81.4 1.4yyy p = 0.000
66.2 0.7
66.2 0.9 p = 0.918 54.7 0.3bbb p = 0.000 82.0 1.5bbb p = 0.000
66.3 0.9
64.8 1.7 p = 0.609 55.0 0.4*** p = 0.000 79.3 3.6** p = 0.003
66.0 1.4
RDLS (points) Boehm-3: correct answers (%)
58.4 0.3 92.3 1.0
58.1 0.4 91.7 1.0
59.5 0.6 95.0 2.0
yyy
p < 0.001 compared to CG children. p < 0.001 compared to CG boys. ** p < 0.01 compared to CG girls. *** p < 0.001 compared to CG girls.
bbb
adequately (except in the area of speech and language in children with ELD) by kindergarten paediatricians, who regularly assess children for different developmental aspects. All children with ELD were able to learn on the same level as their peers. All motor performance and haptic object recognition assessments were performed individually by appropriately qualified therapists who were blinded to the child’s group assignment. Mean age of the participants and results of the language tests are presented in Table 1. The parents gave informed consent for their children’s participation. Approval for this study was given by the Ethics Committee, University of Tartu. 2.2. Functional motor performance Functional motor performance was measured by the Movement Assessment Battery for Children (M-ABC) (Henderson & Sugden, 1992). This test battery consists of 3 subtests: manual dexterity, ball skills, and static and dynamic balance. Each item is scored on a scale from 0 to 5: score 0 is obtained for faultless performance, score 5 in case of failure. Summing the item scores of the 3 subtests generates an age-standardized impairment score (IS) from which a child’s percentile can be calculated. High IS and low percentile indicate poor motor performance. Children scoring below the 5th percentile on the MABC were considered to have definite motor impairment, whereas children scoring between 5th and 15th percentile were considered to have borderline motor difficulties. 2.3. Haptic object recognition A bag with 5 common objects of daily living (key, toothbrush, teaspoon, pencil, clothes-peg) was used to measure haptic perception. The subjects were not familiar with the content of the bag. The child was instructed to put his hand into the bag, take one item at a time, feel it, and guess what it is without visual stimuli. After answering the subject was allowed to take a look at the item. If the child gave the correct answer within 5 s, he was scored 0 and if he gave the answer after 5 s, he was scored 1. The child was scored 2 when he gave at first the wrong answer but corrected himself within 3 s; and 3 if he gave the wrong answer without correction. To eliminate the influence of vocabulary deficiencies, the examiner instructed subjects to either name the item or say what it is used for. If the child could not name the item but said what he can use it for, or when the answer was not grammatically accurate but comprehensible, it was counted correct. Summing the scores for recognizing 5 items formed the total score. Higher scores indicated poorer haptic object recognition ability. 2.4. Hand-grip strength Maximal isometric hand-grip strength of the dominant (HGSD) and non-dominant (HGSND) hand was determined with standard mechanical hand-dynamometer (Lafayette, USA). The test was performed in standing position, hand held unbent on the side. The subjects were instructed to squeeze the handle as forcefully as possible for 2–3 s. Three maximal efforts with both hands were performed and the value of the strongest squeeze was recorded as maximal isometric hand-grip strength. A rest period of 2 min was allowed between the squeezes. 2.5. Vertical jumping performance The vertical jumping test was performed on a force platform (Kistler 9286A, Switzerland) with the dimensions of 0.40 m 0.60 m and natural frequency of 500 Hz. The subjects were instructed to jump as high as possible with preliminary
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counter movement with their hands on the hips. The following characteristics were recorded by a vertical force–time curve for each jump: (1) Jumping height (VJH) by the height of the body centre of gravity: VJH ¼
gt2f 8
;
where g is acceleration of gravity (9.81 m/s2) and tf flight time. (2) Peak vertical ground reaction force (VJGRF). Each subject performed three maximal jumps and the highest jump was used for further analysis. A rest period of 2 min was allowed between the jumps. 2.6. Data analysis Statistical analysis was performed by using SPSS 18 software. Comparative analysis between children with mild ELD and controls was done by using one-way ANOVA followed by Bonferroni post hoc test for normally distributed data (age, scores of RDLS, Boehm-3, HGS and VJ) and the Mann–Whitney U tests (scores of MABC and HOR) for not normally distributed data. A level of p < 0.05 was selected to indicate statistical significance. 3. Results 3.1. Functional motor performance Table 2 displays the mean values of M-ABC results for IS, percentile, manual dexterity, ball skills and balance of both groups. Comparison of groups revealed significant differences for the impairment score (p = 0.000), percentile (p = 0.000), manual dexterity (p = 0.048), ball skills (p = 0.003) and balance (p = 0.001): children with mild ELD performed at considerably lower level in functional motor tests. Two children (1 boy and 1 girl; 6.9%) in ELD group achieved scores below 5th percentile suggesting a significant level of motor impairment. Five children (3 boys and 2 girls; 17.2%) in ELD group and one boy (3.4%) in CG scored between 5th and 15th percentile, showing a moderate level of motor problems. Boys with mild ELD had significantly higher (p = 0.001) impairment score and lower percentile (p = 0.002) compared to CG boys indicating less efficient motor performance, that was more pronounced in subtests of ball skills (p = 0.006) and balance (p = 0.009). For girls with mild ELD statistically relevant differences in M-ABC scores emerged from impairment score (p = 0.020) and percentile (p = 0.020), indicating inferior motor performance compared to CG girls.
Table 2 Mean (SE) values of M-ABC impairment score (IS), percentile and subtests; haptic object recognition (HOR) score and percentage of answers given with latency (HOR: late answers) in children with mild expressive language disorder (ELD) and in control group (CG) children. Parameters
ELD children n = 29
CG children n = 29
IS (points)
7.2 1.1yyy p = 0.000 38.3 5.2yyy p = 0.000 1.9 0.5y p = 0.048 2.7 0.5yy p = 0.003 2.5 0.5yyy p = 0.001 4.7 0.6yy p = 0.010 17.9 3.9 p = 0.619
2.1 0.6
Percentile Manual dext. (points) Ball skills (points) Balance (points) HOR (points) HOR: late answers (%) y
p < 0.05 compared to CG children. p < 0.01 compared to CG children. p < 0.001 compared to CG children. b p < 0.05 compared to CG boys. bb p < 0.01 compared to CG boys. bbb p < 0.001 compared to CG boys. * p < 0.051 compared to CG girls. ** p < 0.01 compared to CG girls. yy
yyy
72.8 4.7 0.7 0.2 0.9 0.3 0.5 0.2 2.6 0.4 15.2 3.5
ELD boys n = 23 6.1 1.0bbb p = 0.001 41.6 6.0bb p = 0.002 1.4 0.4 p = 0.236 2.5 0.5bb p = 0.006 2.2 0.5bb p = 0.009 4.8 0.7b p = 0.026 13.0 3.7 p = 0.398
CG boys n = 23
ELD girls n=6
CG girls n=6
72.3 10.2
0.7 0.3
11.1 3.9* p = 0.020 25.8 8.4* p = 0.020 3.8 1.5 p = 0.066
0.7 0.4
3.5 1.5 p = 0.423
1.3 0.6
0.6 0.3
3.8 1.6 p = 0.093
0.2 0.1
2.6 0.4
4.2 0.7 p = 0.423
2.8 1.0
36.7 9.5** p = 0.010
3.3 3.3
2.1 0.7 72.9 5.5
18.3 4.2
1.9 1.0
0.4 0.3
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Table 3 Mean (SE) values of maximal isometric hand-grip strength of the dominant (HGSD) and non-dominant (HGSND) hand, vertical jumping height (VJH) and peak vertical ground reaction force (VJGRF) in children with mild expressive language disorder (ELD) and in control group (CG) children. Parameters
ELD children n = 29
CG children n = 29
HGSD (N)
10.2 0.5 p = 0.199 9.9 0.6 p = 0.073 0.13 0.01y p = 0.028 253.0 14.8 p = 0.062
11.1 0.3
HGSND (N) VJH (cm) VJGRF (N)
10.4 0.4 0.15 0.01 218.7 10.1
ELD boys n = 23 10.6 0.6 p = 0.610 10.4 0.6 p = 0.978 0.13 0.01 p = 0.335 260.3 16.9b p = 0.042
CG boys n = 23 10.9 0.4 10.4 0.4 0.15 0.01 219.1 10.1
ELD girls n=6 9.0 0.9 p = 0.056 7.9 0.9* p = 0.032 0.14 0.01 p = 0.096 225.0 30.3 p = 0.867
CG girls n=6 11.5 0.7 10.7 0.6 0.17 0.01 217.3 32.7
y
p < 0.05 compared to CG children. p < 0.05 compared to CG boys. * p < 0.05 compared to CG girls.
b
3.2. Haptic object recognition Children with mild ELD had significantly more difficulties (p = 0.01) in HOR test compared to controls (Table 2). Boys with ELD made considerably more errors (p = 0.026) in HOR task than the boys of CG. Although the girls with mild ELD recognized objects haptically in the same level (p = 0.423) as CG girls, they gave significantly more (p = 0.01) answers with latency (>5 s). 3.3. Hand-grip strength The mean values of maximal isometric HGS of both groups are presented in Table 3. No significant differences in HGSD and HGSND were observed between children with mild ELD and CG, F(1, 56) = 1.69, p = 0.199 and F(1, 56) = 3.33, p = 0.073 respectively; as well as between boys with ELD and CG boys, F(1, 44) = 0.26, p = 0.61 and F(1, 44) = 0.001, p = 0.978 respectively. The maximal isometric HGSD of girls with mild ELD did not differ considerably from the same parameter of CG girls, F(1, 10) = 4.69, p = 0.056; but their HGSND was significantly weaker compared to CG girls, F(1, 10) = 6.21, p = 0.032. 3.4. Vertical jumping performance The mean values of vertical jumping performance for the measured groups are displayed in Table 3. VJH of children with mild ELD was lower compared to CG children, F(1, 56) = 5.11, p = 0.028; although there were no statistically significant differences in peak vertical ground reaction force between the groups, F(1, 56) = 3.63, p = 0.062. Boys with mild ELD demonstrated greater VJGRF, F(1, 44) = 4.37, p = 0.042; but statistically equal VJH compared to CG boys, F(1, 44) = 0.95, p = 0.335. The differences in VJH and VJGRF were insignificant between girls with ELD and CG girls, F(1, 10) = 3.39, p = 0.096 and F(1, 10) = 0.03, p = 0.867 respectively. 4. Discussion This research studied motor performance and haptic object recognition ability of children with mild specific expressive language impairment in preschool-age. All these children received speech therapy, but no extra educational assistance and were placed within an ordinary kindergartens. The main findings of this research were: (1) children with mild ELD demonstrated lower level functional motor skills compared to control group; (2) muscle force generation capacity of children with mild ELD is less affected; (3) although there were no statistically significant differences in functional motor abilities of girls with mild ELD, their test scores indicated less efficient motor performance compared to CG girls. The scores of Movement Assessment Battery for Children demonstrated that general functional motor performance of children with mild ELD was less efficient than typically developing children’s in all subtests, as well as expressed by impairment score and percentile. Boys with mild ELD obtained markedly higher scores in ball skills and balance subtests but not in manual dexterity task compared to CG boys. There were no significant differences in manual dexterity, ball skills or balance of girls with mild ELD compared to CG girls. However, their test scores were much higher, especially in subtests of manual dexterity and balance, compared to the same scores of typically developing girls. These results are in accordance with the previous studies (Finlay & McPhillips, 2013; Rechetnikov & Maitra, 2009; Visscher et al., 2007; Webster et al., 2006) where children with DSLD demonstrated deficit in overall M-ABC results. Our results also confirm the conclusion of Visscher et al. (2007), who pointed out that the children with speech disorders perform poorer in the tests of ball skills and static balance. On the other hand, data of our research is only partly in line with the study results of Estil, Whiting, Sigmundsson, and Ingvaldsen (2003), which showed especially poor bimanual coordination of children with SLI. In our study the differences in manual dexterity between the groups of children were not so pronounced and were not statistically relevant when comparing separately the groups of boys and girls. It has to be stressed that the above mentioned studies observed mostly children with moderate or severe speech and language disorders from special schools. Our data revealed lower level
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functional motor abilities also in children with only mild ELD. It has been shown (Selassie et al., 2005) that girls predominate in combined expressive–receptive language problems that affect motor performance more seriously than isolated expressive or receptive problems. In our study there were no children with combined language problems. Although we could not reveal statistically relevant differences in motor performance between groups of girls, there was a tendency for girls with mild ELD to perform less efficiently compared to CG girls in functional motor tests. The absence of statistically relevant differences could be due to small number of girls participating in our study that could mask the real outcome of the assessment. It has been found that important brain structures involved in speech and language production, as well as in sequencing, speed, ball skills and balance control are cerebellum and basal ganglia (Fawcett & Nicolson, 1999; Timmann, Watts, & Hore, 1999; Ullman & Pierpont, 2005). Considering the theories of slower neurodevelopment of children with SLI (Hill, 2001; Vukovic et al., 2010), it can be suggested that the less efficient functional motor performance of children with mild ELD could be elucidated by the immaturity of these brain structures. Further research with larger groups of girls is necessary to confirm the findings of this study as well as to detect the underlying mechanism of ELD. In the haptic object-recognition task children with mild ELD made considerably more errors than controls. Further analysis revealed that boys with ELD had substantially more difficulties with haptic object recognition compared to the same-age counterparts. The girls with mild ELD made also more mistakes in HOR task compared to the girls of CG, although these were not reaching the statistical significance. Considerable difference emerged only in timing parameter of HOR test: girls with mild ELD needed significantly more seconds (>5 s) to give the right answer. These results partly confirmed previous notions (Giannopulu, Cusin, Escolano, & Dellatolas, 2008) that children with DSLD have lower ability to recognize common objects haptically. However, several researchers (Kiesel-Himmel, 2008; Montgomery, 1993) have emphasized that children with DSLD are not deficient in their proprioceptive abilities but they might have problems with performing adequate hand movement patterns or with complex cognitive capabilities like tactile short term memory and cross-modal transfer. The motor coordination of complex movements during haptic object recognition are claimed to be mainly dependent on the posterior cerebellum (Habas & Cabanis, 2008) and the sensorimotor sequences of skill performance on the basal ganglia (Ullman & Pierpont, 2005). Considering the assumption of immature neurodevelopment in children with ELD, inferior haptic performance refers most likely to their inability to select and/or perform appropriate hand movement patterns. As the differences in average subtest score of manual dexterity for children with ELD compared to CG children was not considerable, the difficulties in haptic object-recognition are probably not caused by improper processing of kinaesthetic inputs or by detriment of involved brain structures. Our study demonstrated that maximal force generation capacity in isometric hand-grip strength was statistically on the same level for children with mild ELD and controls. The HGS for both hands of boys with ELD was almost equal to CG boys, which confirms the results of M-ABC about adequate hand function. The hand-grip strength of the non-dominant hand of girls with mild ELD was noticeably weaker than of CG girls. There was also a tendency for weaker HGS of the dominant hand that did not reach statistical relevance. There are few studies (Mu¨u¨rsepp et al., 2011) where force generation capacity of children with SLI has been researched. In the mentioned study, the boys with mild to moderate ELD demonstrated lower maximal voluntary contraction force of the leg extensor muscles. Data of the present study confirmed statistical differences in maximal hand-grip strength only in case of the non-dominant hand of girls with mild ELD. As several central (neural) and peripheral (muscular) factors can determine the differences in muscle voluntary force-generating capacity, one possible explanation may be less developed central processing mechanisms in the hemisphere and cerebellum during voluntary effort of girls with ELD. Interestingly, Estil et al. (2003) pointed out that children with SLI demonstrate poor performance in the static balance test especially with the left leg. Further research is necessary to explain the background and extent of these dysfunctions of girls with mild ELD. Vertical jumps can be used as a model to study explosive force-generating capacity of the lower extremities and ability to coordinate movements of different body parts. The results of this study showed lower vertical jumping height demonstrated by children with mild ELD compared to controls. However, the differences between the boys with ELD and CG boys as well as between girls with ELD and CG girls were not statistically significant. Children with mild ELD demonstrated somewhat higher peak vertical ground reaction force compared to controls, but only the difference between the groups of boys was statistically relevant. Vertical jumping is a multi-joint movement and requires the intra- and intermuscular coordination, which describes the ability of agonists, antagonists and synergists to co-operate in performing the task. This ability depends on the sufficient maturity of nervous system. A few earlier investigators (Merriman, Barnett, & Kofka, 1993; Owen & McKinlay, 1997) have shown the less developed motor coordination in children with SLI compared with typically developing children. Our research results are in accordance with the study of Merriman et al. (1993), showing that peak force of children with SLI is not lower compared to control group children. In the mentioned study, differences emerged only from the components of jumping movement. The lower jumping height of children with mild ELD in the present study is most probably the consequence of deficient ability to coordinate one’s leg extensor muscles. Relatively higher production of peak vertical ground reaction force of the boys and girls with mild ELD compared to controls confirms this theory. This study shows that children even with mild expressive language disorder perform at lower level compared to controls in tests of functional motor skills, but not in tests demanding muscle force generation capacity. The motor proficiency of boys with mild ELD is clearly affected compared to the same-aged peers. The girls with mild ELD also demonstrate the tendency to have more difficulties in functional motor tasks. From a clinical perspective, a broader assessment procedure for children at
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