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Delayed motor skill acquisition in kindergarten children with language impairment
Research in Developmental Disabilities 32 (2011) 2963–2971
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Research in Developmental Disabilities
Delayed motor skill acquisition in kindergarten children with language impairment Esther Adi-Japha *, Orli Strulovich-Schwartz, Mona Julius School of Education, Bar-Ilan University, Ramat-Gan 52900, Israel
A R T I C L E I N F O
A B S T R A C T
Article history: Received 12 April 2011 Received in revised form 28 April 2011 Accepted 4 May 2011 Available online 31 May 2011
The acquisition and consolidation of a new grapho-motor symbol into long-term memory was studied in 5-year-old children with language impairment (LI) and peers matched for age and visual-motor integration skills. The children practiced the production of a new symbol and were tested 24 h and two weeks post-practice day. Differences in performance speed emerged between the groups: children with LI showed a later onset of rapid learning in the practice phase, and only the comparison group exhibited delayed, consolidation, gains 24 h post-training. At two weeks post-training, children with LI improved, closing the gap in performance speed. Speed-accuracy trade-off was characteristic of speed improvements in LI. These results indicate atypical and delayed acquisition in children with LI, and support the view that deficient skill acquisition in LI goes beyond the language system. ß 2011 Elsevier Ltd. All rights reserved.
Keywords: SLI Procedural memory Implicit memory Figure-copying Learning curve Kindergarten
1. Introduction The cognitive processes and neural substrates that mediate our capacity to acquire new motor skills have been studied in recent years among the adult human population (Doyon & Benali, 2005; Korman, Raz, Flash, & Karni, 2003; Stickgold & Walker, 2005) and among school-age children (Dorfberger, Adi-Japha, & Karni, 2007; Meulemans, Van Der Linden, & Perruchet, 1998; Prehn-Kristensen et al., 2009). It was shown that following a training experience, significant trainingdependent gains in performance can appear hours after the termination of training, for example 24 h post-training (Dorfberger et al., 2007; Savion-Lemieux, Bailey, & Penhune, 2009). These gains were maintained for weeks and months. It has been proposed that these delayed gains reflect neuronal memory consolidation processes that require time, and in some cases sleep, to reach completion (Maquet et al., 2003; Walker, 2005). Developmental dyslexia (DD) and attention deficit hyperactivity disorder (ADHD) were recently associated with atypical acquisition and expression of memory consolidation gains (Adi-Japha, Fox, & Karni, 2011; Vicari et al., 2005). Preschool children acquire a variety of motor skills which are important for their physical and academic development (Riethmuller, Jones, & Okely, 2009). Motor skills in preschoolers were shown to predict later achievements in reading and math and proved useful in identifying children at risk for school achievements (Grissmer, Grimm, Aiyer, Murrah, & Steele, 2010; Pianta & McCoy, 1997; Son & Meisels, 2006). However, the time-course of motor skill acquisition in preschool children has not been studied to date. In light of the association between language and motor impairments (Hill, 2001; Iverson, 2010), the current study examined the time-course of acquisition of a (grapho-) motor skill in typically developing preschool children and their peers with language impairment.
* Corresponding author. Tel.: +972 3 5318704; fax: +972 3 6354997. E-mail addresses: [email protected], [email protected] (E. Adi-Japha). 0891-4222/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ridd.2011.05.005
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The incidence of primary (specific) language impairment (LI) among kindergarten children is estimated to be 7% (Tomblin et al., 1997). Children with LI present delayed or disordered language acquisition that is not secondary to conditions such as hearing loss, developmental delay, neurological insult, or environmental deprivation. Although language performance is, by definition, the central impairment in these children, deficits seem not to be limited (or specific) to language and to include weaknesses in basic nonlinguistic processing skills (Archibald & Gathercole, 2006; Ullman & Pierpont, 2005; Windsor, Kohnert, Loxtercamp, & Kan, 2008). Within the nonlinguistic domain, there is considerable evidence that the performance of children with LI on a variety of motor tasks is slower, and is more vulnerable to the effect of cumulative experience (e.g., Bishop, 2002; Estil, Whiting, Sigmundsson, & Ingvaldsen, 2003; Hill, 2001). For example, LI groups showed deficits in fine and gross motor tasks, such as peg moving, bead threading, ball rolling and tapping (Bishop & Edmundson, 1987; Corriveau & Goswami, 2009; Miller, Kail, Leonard, & Tomblin, 2001; Powell & Bishop, 1992). A range of causal mechanisms, which are not mutually exclusive, have been proposed for LI, some of which address impairment in motor control. For example: difficulties in elementary cognitive operations and/or working memory (e.g., Archibald & Gathercole, 2006; Kail, 1994), a genetic factor that affects language as well as motor development (Bishop, 2002), anatomical anomalies in related motor and language networks (e.g., Soriano-Mas et al., 2009), or the hypothesis of an atypical procedural memory system in LI (Ullman & Pierpont, 2005) and in related developmental disorders such as DD and ADHD (Nicolson & Fawcett, 2007). The term procedural memory refers to the long-term memory system subserving the acquisition and retention of skills (’how to’ knowledge) and habits, specifically, the repetition-dependent, implicit knowledge of the structure of recurring experiences (Brown & Robertson, 2007; Cohen & Squire, 1980). The acquisition of new motor skills (for example, handwriting) is typically cited to demonstrate learning that is supported by the procedural memory system. Ullman (2004) highlighted the fact that the procedural memory system is involved in the acquisition of language skills and habits, such as our implicit knowledge of language rules, in addition to the acquisition of new motor skills. Tomblin, Mainela-Arnold, and Zhang (2007) recently studied the procedural learning of a sequence among adolescents diagnosed with specific LI in kindergarten, using the serial reaction time (SRT, Nissen & Bullemer, 1987) task. These authors observed that the learning curve of the SRT task consisted of a period of slowed responses prior to the onset of rapid learning. Lum, Gelgec, and Conti-Ramsden (2010) studied the SRT task in 7- and 8-year-old with and without LI. Their findings indicated lower accuracy and slower performance for children with LI. Observation of the reaction time learning curve presented therein verifies the later onset of rapid learning by children with LI. It is not clear, however, whether these results are specific to sequence learning, and whether deficient consolidation processes exist in addition to slower task performance. For example, Vicari et al. (2005) tested 16 school-age children with DD and matched typical readers on the SRT and on the mirror drawing tasks. The mirror drawing task is a procedural learning task that requires the establishment of fast and repetitive production of visuospatial stimuli but no acquisition of sequences. The participant is asked to repetitively trace a shape (e.g., star) through a mirror that inverts the image. Participants were trained on the mirror-drawing task, and memory consolidation was tested 24 h post-training session. Vicari et al. (2005) demonstrated that children with DD have lower accuracy and slower performance on the SRT task. Furthermore, although these children performed similarly to normal readers on the training phase of the mirror drawing task, they performed significantly less well on the retention of task, showing impaired consolidation processes of newly acquired motor skills. The current experiment was designed to study the time-course of learning a grapho-motor skill, the production of an invented 2-segment letter, in preschool children with LI and age-matched peers with comparable visual-motor integration skills. The children practiced production on day 1, and were tested 24 h and 2 weeks post-practice day. The invented letter task is a dot connecting task, and requires the establishment of fast and repetitive production of visuospatial stimuli but no acquisition of sequences. The task was developed to study skill acquisition and long-term retention in preschool children: (a) because typical skill learning tasks were found to be too difficult for young children (e.g., Wilhelm, Diekelmann, & Born, 2008), and (b) because of its direct relevance to the development of grapho-motor skills, a central skill in young children’s everyday life. Invented letter writing (Longcamp, Anton, Roth, & Velay, 2003, 2005a), grapho-motor mirror drawing tasks (Sosnik, Hauptman, Karni, & Flash, 2004; Vicari et al., 2005), circle drawing (Vinter & Detable, 2008; Vinter & Perruchet, 2000) as well as real letter writing (Adi-Japha et al., 2007; Adi-Japha & Freeman, 2000, 2001; Balas, Nester, Giladi, & Karni, 2007; Dorfberger, Adi-Japha, & Karni, 2009; James, 2010; James & Gauthier, 2006) have been used extensively in both behavioral and brain imaging experiments (e.g., James, 2010; Longcamp et al., 2008) for studying the effect of training on letter-form recognition and grapho-motor performance. Grapho-motor activity, whether tested by tracing figures (Estil et al., 2003), design copying (Marton, 2008), or handwriting fluency (Dockrell, Lindsay, Connelly, & Mackie, 2007), was found to be impaired in children with LI. Because consolidation and retention in the long-term memory of new skills is training-dependent (Hauptman, Reinhart, Brandt, & Karni, 2005; i.e., a minimal number of task repetitions during training may be necessary to trigger delayed consolidation gains), we ensured a similar level of visual-motor integration between children with LI and their peers. Studies have indicated that of all perceptual motor skills, visual-motor integration correlates most with handwriting performance (Daly, Kelley, & Krauss, 2003). In the present study, visual-motor integration was assessed using a copy-a-design paradigm, a paradigm that has been shown to be predictive of later school achievements (Grissmer et al., 2010). We assumed that similar visual-motor integration skills between groups would suffice to ensure a similar baseline. If children with LI would show a slower rate of task acquisition during the practice phase (Lum et al., 2010; Tomblin et al., 2007) or would fail to show consolidation gains 24 h post-practice, this would support the hypothesis of atypical procedural learning in LI (Ullman & Pierpont, 2005).
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2. Methods 2.1. Participants All 32 Israeli kindergarten children who participated in this study spoke Hebrew as their first language and used their right hand when drawing. Participating children were recruited from kindergartens in a central middle-high socioeconomic status (SES) city in Israel. Sixteen children with LI (4 girls) aged between 64 and 75 months were recruited from language kindergartens. These children were admitted to the kindergarten based on significant primary language impairment, normal nonverbal intelligence and sound adaptive behavior skills. The placement committee (comprised of the special education kindergarten district supervisor, municipal kindergarten psychologist, and special education therapists) assesses eligibility based on standardized cognitive assessments, speech-language pathologist referral, and information from previous kindergarten teachers and caregivers. All children referred to the placement committee are administered the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) adapted to Hebrew (Liblich, 1979). Children are referred to the placement committee as having a language disorder based on a failure on at least two language tests that are used in clinical practice in Israel, in the presence of normal performance IQ (Friedmann & Novogrodsky, 2004). After receiving Ministry of Education approval for the experimental procedure, parental informed consent forms were sent to parents of children who were identified by kindergarten teachers as having normal hearing, no additional communication disorders, no formal diagnosis or signs of attention deficit disorder, and do not regularly take any medication. Sixteen children with typical development (4 girls) matched by age and raw scores on a visual-motor integration (VMI) test were recruited from two kindergartens in the same city to serve as a comparison group. All children with LI scored more than a standard deviation below the mean of their age (and VMI) matched peers on the WPPSI vocabulary subtest (group difference of 1.5 SD on the standardized score). A standardized score of 75 or higher (i.e., above the 5th percentile) in the VMI test comprised an inclusion criterion for all participants. This criterion is based on a recent large-scale study showing that performance below the 5th percentile is appropriate for the definition of severe motor impairment which impacts children’s daily life (Lingam, Hunt, Golding, Jongmans, & Emond, 2009). All children scored 88 or more on the ‘‘draw a man test’’ for intellectual maturity (Harris, 1963, see details below; M = 97.68, SD = 8.93; M = 99.38, SD = 5.83, for children with LI and the comparison group, respectively, t(30) = .60, n.s). 2.2. Measures 2.2.1. Language tests All children were tested for receptive vocabulary using the Peabody Picture Vocabulary Test III (PPVT-III, Dunn & Dunn, 1997). Expressive vocabulary was assessed using the vocabulary subtest of the WPPSI adapted to Hebrew (Liblich, 1979). 2.2.1.1. PPVT-III. The children were tested using an expert translation of the PPVT-IIIB developed at Bar-Ilan University (AdiJapha, Berberich-Artzi, & Libnawi, 2010). In this test, the children were requested to point to a picture (one of 4 presented) that matches a word the examiner said. Testing continued until the child made 8 errors out of a block of 12 trials. Raw scores are reported. 2.2.1.2. WPPSI vocabulary subtest. In this test the children were requested to define words that the examiner read. Testing continued until the child made 5 consecutive errors. The mean standardized score is 10, and the standard deviation is 3. 2.2.2. Control test All children were tested on the Draw-a-man test (Harris, 1963), used here as a nonverbal intelligence test, to ensure a similar intellectual maturity level in the two groups, and on the Beery–Buktenica developmental test of Visual-Motor Integration (Beery-VMI) (Beery, Buktenica, & Berry, 2006) which was used to assess the extent to which the participants could integrate their visual and grapho-motor abilities. 2.2.2.1. Draw-a-man test. The developmental progression of children’s human figure drawings has been found to be sufficiently standard to allow estimates of intellectual maturity (Goodenough, 1926; Harris, 1963; Khaleefa, Abdelwahid, Abdulradi, & Lynn, 2008; Koppitz, 1968; Naglieri, 1988; Sharma, 2004). The test was used here to show that children’s graphic production does not indicate risk for general intellectual functioning. 2.2.2.2. VMI test. This test contains a sequence of 27 geometric forms of increasing complexity ranging from a simple vertical line to a complex three-dimensional star. The children were asked to copy each item as accurately as possible. Testing continued until the child made 3 consecutive errors. 2.2.3. Memory span tests The number recall and the hand movement measures from the sequential subtests of the Kaufman Assessment Battery for Children (K-ABC, Kaufman & Kaufman, 1983), adapted to Hebrew (Phizer, Shimborsky, Walf, & Hazani, 1995), were used to assess the short-term memory span.
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2.2.3.1. Number recall. The experimenter read a random string of digits of varying lengths (2–7 digits) out loud. The children were asked to repeat the string in the same order. Testing continued until the child made 3 consecutive errors. 2.2.3.2. Hand movement test. The children were presented with a random sequence of movements (palm down, fist, and side) of varying lengths (2–5 movements) and were requested to imitate the movements. Testing continued until the child made 3 consecutive errors. 2.2.4. The invented letter task The invented letter task was used in order to study the time-dependent course of motor skill acquisition. The task consists of point-to-point planar movements, and does not require memory load because the visual stimuli and direction of movement are available to the participants throughout the task. The current task was adjusted in difficulty to previously used letter learning tasks in kindergarten children (e.g., Longcamp, Zerbato-Poudou, & Velay, 2005b). In the invented letter task, children are asked to connect three encircled dots with lines (Fig. 1A: A ! B ! C, segment length 1.2 cm, circle diameter 2 mm) to form an invented letter. Movement progress was from right to left (as in Hebrew writing). Each experimental block was comprised of 3 rows of 5 dot-to-dot shapes that they should connect (Fig. 1B). The experimenter (second author of the paper, O.S.) explained the task to the children, and asked them to complete the task as rapidly and accurately as possible. The children were given one practice line in a paced manner at the beginning of each of the three experimental days. The experiment was held on two successive days (days 1 and 2), and long-term retention (retention session) was tested on a third day (day 3), two weeks later. Day 1 included training on 12 experimental blocks. On days 2 (consolidation session) and 3 (retention session) the children were tested during one experimental session consisting of 4 blocks. On all testing days the blocks were separated by a minimum of 15 s and up to a 30 s break. The experimental task was performed by the children on half of an A4 sheet of paper, using a HB pencil. After completion of each experimental block, the experimenter placed an identical sheet of paper in front of the child, for completion. The same task was repeated for the experimental sessions during the three intervals. No feedback was provided on any performance measure, only general encouragement (‘‘you are doing fine’’; ‘‘pay attention to the task’’; ‘‘remember to be as quick and accurate as possible!’’). The children completed the 12 experimental blocks on day 1 within 20 min. The 4 consolidation and retention blocks were completed within 5 min. 2.3. Statistical analysis Three experimental sessions were defined on day 1: pre-training (blocks 1–4), training (blocks 5–8) and post-training (blocks 9–12), in order to enable comparison between the current experimental design and other studies of skill acquisition (Dorfberger et al., 2007; Wilhelm et al., 2008), as well as to allow for comparison between day 1 and days 2 and 3. Days 2 and 3 consisted of one experimental session of 4 blocks. We chose 4 blocks as an experimental unit, similarly to other studies (Dorfberger et al., 2007; Wilhelm et al., 2008), in order to minimize measurement noise due to an erroneous block. Two measures were calculated to evaluate performance: speed of performance assessed as the time of completing an experimental block, and accuracy assessed as the average number of lines drawn within the circled area per block. Four testing sessions across the two week-period were used in the analysis: (a) Pre-training session (blocks 1–4 on day 1); (b) Post-training session (blocks 9–12 on day 1). (c) Consolidation session (4 blocks) assessed on day 2, 24 h post-training; and (d) Retention session (4 blocks) assessed two weeks following day 1. Speed and accuracy of performance were analyzed separately across the two week-period using: (a) a 4 (Session = pre-training; post-training; 24-h post-training; 2-weeks posttraining) 4 (Blocks) 2 (Group = comparison; SLI) repeated measures analysis of variance; or (b) within each of the three
Fig. 1. The ‘‘invented letter’’ stimuli. (A) A single stimulus. (B) One of the three rows of stimuli. The three rows constitute an experimental block.
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learning phases: training phase (pre-training vs. post-training), consolidation phase (post-vs. 2-weeks post-training) 4 (Blocks) 2 (Group = comparison; SLI). 3. Results Table 1 provides descriptive data of the participants. It can be seen that the participants in the two groups were comparable on the raw scores of the motor Beery-VMI tests. The LI group scored lower on the PPVT-III, the vocabulary subtest of the WPPSI and the number recall test. The latter is also considered a short-term verbal memory test (Gray, 2006). 3.1. The invented letter task 3.1.1. Performance time analysis The average block time in the 20 experimental blocks is shown in Fig. 2A. A Kolmogorov–Smirnoff test applied to block performance times did not reveal deviations from the normal distribution. A 2 (group = comparison, LI) 4 (session = pretraining, post-training, 24 h post-training, 2 weeks post-training) 4 (blocks per session) analysis of variance (ANOVA) for repeated measures indicated a main effect of group (F(1, 30) = 4.23, p < .05, h2p ¼ :13), a main effect of session (F(3, 90) = 21.09, p < .001, h2p ¼ :43), a main effect of block (F(3, 90) = 3.95, p < .05, h2p ¼ :12), and a significant group session block interaction term (F(9, 270) = 1.95, p < .05, h2p ¼ :07). As can be seen in the figure, the two groups displayed different learning curves in terms of performance time. Although children with LI were slower in all phases, a significant difference emerged only 24 h post-training (F(1, 30) = 7.14, p < .05, h2p ¼ :19). In the post hoc analyses (presented below) we studied the source of the group session block interaction found for performance time by analyzing day 1 practice gains (post- vs. pre-training), consolidation phase gains (24 h post-training vs. post-training), and retention phase (2 weeks posttraining vs. 24 h post-training). 3.1.1.1. Day 1 training gains. A 2 (group = LI, comparison) 2 (session = pre-training, post-training) 4 (block) ANOVA for repeated measures applied to performance time data indicated a significant main effect for session (F(1, 30) = 30.48, p < .001, h2p ¼ :50) as well as a significant group session block interaction term (F(3, 90) = 3.34, p < .03, h2p ¼ :10), with no other main effects or interactions. Post hoc ANOVA of group x block analysis applied to the two sessions (pre- and post-training) indicated a significant interaction only for the pre-training session (F(3, 90) = 3.83, p < .02, h2p ¼ :11). The interaction term suggests a higher level of improvement during the 4 pre-training blocks in the comparison than in the group of participants with LI. When tested in each group, improvement throughout the first four blocks showed a trend towards improvement for the comparison group (F(3, 45) = 2.54, p < .07, h2p ¼ :14) and was not significant for children with LI (F(3, 45) = 1.54, p > .2). In order to gain a more complete view of the first day learning, we tested the difference in the linear slope across each of the 4-block day 1 segments: pre-training (blocks 1–4), training (blocks 5–8) and post-training (blocks 9–12) in each group. A typical learning curve should show a significant reduction in performance time at the pre-training, vs. a plateau at post-training (AdiJapha, Karni, Parnes, Loewenschuss, & Vakil, 2008; Hauptman et al., 2005; Korman et al., 2003). A 2 (group = LI, comparison) 3 (training segments slopes = pre-training slope, training slope, post-training slope) analysis of variance for repeated measures indicated a significant interaction term (F(2, 60) = 3.49, p < .04, h2p ¼ :10). Post hoc analysis revealed that the source of interaction was the difference in slopes between the pre-training and the training segments of the two groups (F(1, 30) = 4.12, p < .05, h2p ¼ :12): the linear slope of the 4 pre-training blocks (blocks 1–4) decreased only for the comparison group, indicating an improvement in performance time (t(15) = 2.98, p < .01). The linear slope of the 4 training blocks (blocks 5–8) decreased in both groups (t(15) = 2.40, 2.25, p < .03, .04, for children with LI and the comparison group, respectively). In both groups the slope of the 4 post-training blocks (blocks 9–12) did not indicate a significant deviation from zero, which is consistent with a plateau performance. These results suggest a later onset of learning in the group of children with LI. Previous research suggests that when a single learning process is at work, a power-law function can well reflect the group-averaged performance curve (Ashby, Ennis, & Spiering, 2007; Logan, 1988; Newell & Rosenbloom, 1981; Segalowitz & Table 1 Descriptive data of the two groups. Children with LI
Age (months) VMI (raw) PPVT (raw) WPPSI (stand.) Number recall (stand.) Hand movement test (stand.)
Comparison group
t
M
SD
M
SD
69.81 10.62 59.68 6.75 8.25 8.24
2.66 2.70 16.66 1.40 3.99 6.44
67.93 12.06 70.56 11.18 11.93 10.92
3.92 2.72 13.48 2.85 3.15 6.12
1.58 1.49 2.03* 4.84*** 2.61* 1.18
VMI = Beery-VMI raw scores; PPVT = Peabody Picture Vocabulary Test III; WPPSI = vocabulary subtest of the Wechsler Preschool and Primary Scale of Intelligence. * p < .05. *** p < .001.
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# On target shapes per block
Time per block (sec.)
A 60
Control LI
50 40 30
14
Pre
Post
24h-post
2wks-post
Post
24h-post
2wks-post
B
12 10 8
Pre
Fig. 2. Speed and accuracy data (mean and standard error) of the comparison group and of the group of children with LI at 4 time points (indicated by a lower bar): pre-training (pre, blocks 1–4 on day 1), post-training (post, blocks 9–12 on day 1), 24 h post-training (24 h-post), and 2 weeks post-training (2 wkspost). (A) Time per block. (B) Number of shapes in which the child’s pencil moved within the outer circle.
Segalowitz, 1993). A deviation from a power-law fit may reflect a transition between performance modes. The previous analyses suggest that a transition between performance modes occurred among participants with LI. Although the fit to a power-law was significant for both children with LI and the comparison group (R2 = .63, 90, p < .01, .001, for children with LI and comparison group, respectively), the Wald-Wolfowitz runs algorithm (Adi-Japha et al., 2008; Wagenmakers & Brown, 2007) that tests whether the residuals of the power-function fit are random by assessing the number of times their signs (positive or negative) alternate, demonstrated a significant deviation from randomness for the group of children with LI (Z = 1.96, p < .05). As of block 7 their performance was consistently below what could be expected based on a power-law function fit. Overall, the above analyses suggest that the onset of effective learning occurred later for children with LI (on average, as of block 7) than for children in the comparison group. 3.1.1.2. Consolidation gains. A 2 (group = LI, comparison) 2 (session = post-training, 24 h post-training) 4 (block) ANOVA for repeated measures applied to performance time data indicated a main effect of group (F(1, 30) = 5.05, p < .05, h2p ¼ :14) and a significant group x session interaction (F(1, 30) = 4.18, p < .05, h2p ¼ :12). The source of the interaction was the improvement in performance time made by the comparison group between the post-training and 24 h post-training sessions (F(1, 15) = 30.31, p < .001, h2p ¼ :66), whereas the performance time of the LI group did not reveal a significant change. While 15/16 participants in the comparison group improved their performance between day 1 and 2, only 8/16 participants in the LI group did so (x2(1) = 7.57, p < .01). A group block analysis of the 24 h post-training session indicated a significant difference between the two groups (F(1, 30) = 7.14, p < .02, h2p ¼ :19) in favor of the comparison group. In contrast, the posttraining session analysis did not yield any significant effects. 3.1.1.3. Retention phase. A 2 (group = LI, comparison) 2 (session = 24 h post-, 2 weeks post-training) 4 (block) ANOVA applied to performance time data showed a block main effect (F(3, 90) = 4.23, p < .01, h2p ¼ :13) indicating improvement with blocks, and a significant group x session interaction (F(1, 30) = 7.96, p < .01, h2p ¼ :22). The source of the interaction was the improvement in performance time made by the LI group between the 24 h post-training and 2 weeks post-training sessions (F(1, 15) = 6.70, p < .03, h2p ¼ :30), whereas performance time of the comparison group did not reveal a significant change. In spite of their improvement, performance speed of children with LI 2 weeks post-training was at its post-training level (F(1, 15) = 1.31, p > .2), while for the comparisons it was significantly better than post-training performance (F(1, 15) = 6.56, p < .03, h2p ¼ :30). A group block analysis of the 2 weeks post-training session showed a significant block effect (F(3, 90) = 4.42, p < .01, h2p ¼ :13), indicating improvement between blocks, with no group main effects. 3.1.2. Analysis of accuracy data The average accuracy in the 20 experimental blocks is shown in Fig. 2B. A similar 2 (group = LI, comparison) 4 (session = pre-training, post-training, 24 h post-training, 2 weeks post-training) 4 (block) ANOVA for repeated measures applied to accuracy data indicated no significant main effects or interactions, suggesting that accuracy level was equal across groups and was maintained throughout the experimental period. Although children with LI were more accurate than the comparison group at all but two task blocks (Fig. 2B), this difference was not significant for any of the blocks (t(30) < 1.60, ps > .12), or overall (F(1, 30) = 2.40, p > .13; with less than one shape of 15, per block, difference) due to the large group variability (see Fig. 2B for mean and standard errors). It should be noted that, contrary to performance time differences
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between the groups, accuracy differences were consistent and not affected by training or time between experimental sessions. 3.1.3. Speed accuracy trade-off Speed-accuracy trade-off was studied using correlation analyses between the gains in speed and accuracy within the three study phases (training, consolidation and retention). The analyses suggested that for the group of children with LI, improvement in speed (i.e., reduction in performance time) was accompanied by reduction in accuracy in the training (from pre- to post-training, r = .62, p < .02) as well as in the retention phase (from 24 h post- to 2 weeks post-training, r = .61, p < .02).
4. Discussion Our findings indicate that when given a grapho-motor learning task, kindergarten children with LI presented an atypical learning curve, significantly differing from the comparison group in the practice phase, and in the post-training memory consolidation phase. Given the same training experience, children with LI showed a late onset of rapid learning (Tomblin et al., 2007). Twenty-four hours post-training only the comparison group showed delayed gains in speed of performance which were retained 2 weeks post-training. Children with LI gained in speed from pre- to post-training, as well as from 24 h post- to 2 weeks post-training, but at a cost in accuracy. Although at 2 weeks post-training they closed the gap in performance speed, they did not perform significantly better than their day 1 post-training level of performance. The matching procedure used in this study suggests that group differences cannot be explained by grapho-motor performance per se, as indicated by the Beery VMI scores. It should be noted, however, that the Beery-VMI test only measures accuracy of performance, and that the sample was small. This study is correlational in nature, and other factors not assessed here may explain the reported group differences. Furthermore, although the children with LI in this sample were not diagnosed as having other developmental deficits, these may be diagnosed at a later age. Group learning curves for a variety of tasks, with averaging across individual participants and across blocks of trials, are often characterized by negatively accelerated, gradually improving performance, typically characterized by a power-law (Ashby et al., 2007; Adi-Japha et al., 2008; Logan, 1988; Newell & Rosenbloom, 1981; Segalowitz & Segalowitz, 1993). However, performance of children with LI significantly deviated from the expected power-law learning curve. The comparison group showed an improvement in performance during the first four blocks of day 1, whereas children with LI showed improvement only after block 5 (with significant positive slope of gains in speed from blocks 5–9). These results add to the results of Tomblin et al. (2007) and of Lum et al. (2010), who reported a within-session sequence learning deficit in children with LI using the SRT task. Furthermore, Tomblin et al. (2007), who studied adolescents who were diagnosed with LI in kindergarten, reported late initiation of learning in the SRT task. However, possibly because of task complexity, participants with LI showed no evidence of an asymptote by the last trial block of the SRT task. In the current study, the simplicity of the task enabled participants with LI to set into an asymptote by the end of training in spite of late initiation of learning. These results suggest that children with LI are slower in forming motor patterns. Only the comparison group improved between day 1 and day 2, showing the expected delayed consolidation gains in speed of performance. By 24 h post-training, the speed of performance of the comparison group was significantly better than that of children with LI. Vicari et al. (2005) studied skill acquisition in school-age children with DD using the mirror drawing task. Although the dyslexic children and the comparison group performed similarly on the first day of training, the former were significantly slower than the normal readers 24 h post-training. These results are similar to the results of the current study and may suggest a mechanism of impaired procedural learning in both developmental disorders, although its origin may differ between these two etiologies. An atypical procedural memory system was suggested (Nicolson & Fawcett, 2007) as being involved in other developmental disorders, for example in ADHD (Adi-Japha et al., 2011). Children with ADHD are known to have impaired grapho-motor performance (Adi-Japha et al., 2007; Barkley, 1998). Children with LI significantly improved their performance from the 24 h post-training session to the 2 weeks posttraining session. This result was not expected, and may have occurred because the 24 h post-training session added to their training on the task. In spite of this improvement, their performance speed at 2 weeks post-training was not significantly better than their post-training performance speed. This result suggests that children with LI may require more training (Law, Rush, Schoon, & Parsons, 2009) or perhaps need more off-line time (or both) to show delayed gains. It may be hypothesized that retesting their abilities even later, possibly following some additional training, may demonstrate further improvement. High fluency and high accuracy are a hallmark of skilled performance (Anderson, 1982; Logan, 1988). Gains in speed of performance with no reduction, and sometimes with a concurrent increase in accuracy have been shown to evolve from practice in many laboratory tasks, in which perceptual, motor and cognitive skills were learned (Adi-Japha et al., 2011; AriEven Roth, Kishon-Rabin, Hildesheimer, & Karni, 2005; Ferman, Olshtain, Schechtman, & Karni, 2009; Karni et al., 1995; Karni & Sagi, 1993; Korman et al., 2003). Gains in speed in dot-to-dot grapho-motor learning tasks were found to evolve while accuracy at mid-dots was maintained (Sosnik et al., 2004). The current results show that while there was an improvement in speed with no reduction in accuracy during the training in the comparison group, in the SLI group both the expression of gains in speed during the training and at the retention interval was accompanied by a decrease in accuracy. A fast and inaccurate response style is one of the most salient features of ADHD (Adi-Japha et al., 2007, 2011; Eliasson, Rosblad, &
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Forssberg, 2004). Possibly, these results should be interpreted in light of the co-occurrence of LI with ADHD (Cardy, Tannock, Johnson, & Johnson, 2010; Love & Thompson, 1988), commonly not diagnosed before 7 years of age. The causes and biological basis of LI are poorly understood (Webster & Shevell, 2004). Although it is clear that our study does not solve the current debate about the underlying nature of SLI, it contributes new data to existing knowledge and broadens our understanding of the SLI phenotype. Specifically, the results of the current study corroborate the hypothesis of a typical procedural memory system in children with LI. The current results suggest that assessment batteries should incorporate assessment of motor skill learning as well as language in order to identify learning, rather than performance, deficits. 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Contents lists available at ScienceDirect
Research in Developmental Disabilities
Delayed motor skill acquisition in kindergarten children with language impairment Esther Adi-Japha *, Orli Strulovich-Schwartz, Mona Julius School of Education, Bar-Ilan University, Ramat-Gan 52900, Israel
A R T I C L E I N F O
A B S T R A C T
Article history: Received 12 April 2011 Received in revised form 28 April 2011 Accepted 4 May 2011 Available online 31 May 2011
The acquisition and consolidation of a new grapho-motor symbol into long-term memory was studied in 5-year-old children with language impairment (LI) and peers matched for age and visual-motor integration skills. The children practiced the production of a new symbol and were tested 24 h and two weeks post-practice day. Differences in performance speed emerged between the groups: children with LI showed a later onset of rapid learning in the practice phase, and only the comparison group exhibited delayed, consolidation, gains 24 h post-training. At two weeks post-training, children with LI improved, closing the gap in performance speed. Speed-accuracy trade-off was characteristic of speed improvements in LI. These results indicate atypical and delayed acquisition in children with LI, and support the view that deficient skill acquisition in LI goes beyond the language system. ß 2011 Elsevier Ltd. All rights reserved.
Keywords: SLI Procedural memory Implicit memory Figure-copying Learning curve Kindergarten
1. Introduction The cognitive processes and neural substrates that mediate our capacity to acquire new motor skills have been studied in recent years among the adult human population (Doyon & Benali, 2005; Korman, Raz, Flash, & Karni, 2003; Stickgold & Walker, 2005) and among school-age children (Dorfberger, Adi-Japha, & Karni, 2007; Meulemans, Van Der Linden, & Perruchet, 1998; Prehn-Kristensen et al., 2009). It was shown that following a training experience, significant trainingdependent gains in performance can appear hours after the termination of training, for example 24 h post-training (Dorfberger et al., 2007; Savion-Lemieux, Bailey, & Penhune, 2009). These gains were maintained for weeks and months. It has been proposed that these delayed gains reflect neuronal memory consolidation processes that require time, and in some cases sleep, to reach completion (Maquet et al., 2003; Walker, 2005). Developmental dyslexia (DD) and attention deficit hyperactivity disorder (ADHD) were recently associated with atypical acquisition and expression of memory consolidation gains (Adi-Japha, Fox, & Karni, 2011; Vicari et al., 2005). Preschool children acquire a variety of motor skills which are important for their physical and academic development (Riethmuller, Jones, & Okely, 2009). Motor skills in preschoolers were shown to predict later achievements in reading and math and proved useful in identifying children at risk for school achievements (Grissmer, Grimm, Aiyer, Murrah, & Steele, 2010; Pianta & McCoy, 1997; Son & Meisels, 2006). However, the time-course of motor skill acquisition in preschool children has not been studied to date. In light of the association between language and motor impairments (Hill, 2001; Iverson, 2010), the current study examined the time-course of acquisition of a (grapho-) motor skill in typically developing preschool children and their peers with language impairment.
* Corresponding author. Tel.: +972 3 5318704; fax: +972 3 6354997. E-mail addresses: [email protected], [email protected] (E. Adi-Japha). 0891-4222/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ridd.2011.05.005
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The incidence of primary (specific) language impairment (LI) among kindergarten children is estimated to be 7% (Tomblin et al., 1997). Children with LI present delayed or disordered language acquisition that is not secondary to conditions such as hearing loss, developmental delay, neurological insult, or environmental deprivation. Although language performance is, by definition, the central impairment in these children, deficits seem not to be limited (or specific) to language and to include weaknesses in basic nonlinguistic processing skills (Archibald & Gathercole, 2006; Ullman & Pierpont, 2005; Windsor, Kohnert, Loxtercamp, & Kan, 2008). Within the nonlinguistic domain, there is considerable evidence that the performance of children with LI on a variety of motor tasks is slower, and is more vulnerable to the effect of cumulative experience (e.g., Bishop, 2002; Estil, Whiting, Sigmundsson, & Ingvaldsen, 2003; Hill, 2001). For example, LI groups showed deficits in fine and gross motor tasks, such as peg moving, bead threading, ball rolling and tapping (Bishop & Edmundson, 1987; Corriveau & Goswami, 2009; Miller, Kail, Leonard, & Tomblin, 2001; Powell & Bishop, 1992). A range of causal mechanisms, which are not mutually exclusive, have been proposed for LI, some of which address impairment in motor control. For example: difficulties in elementary cognitive operations and/or working memory (e.g., Archibald & Gathercole, 2006; Kail, 1994), a genetic factor that affects language as well as motor development (Bishop, 2002), anatomical anomalies in related motor and language networks (e.g., Soriano-Mas et al., 2009), or the hypothesis of an atypical procedural memory system in LI (Ullman & Pierpont, 2005) and in related developmental disorders such as DD and ADHD (Nicolson & Fawcett, 2007). The term procedural memory refers to the long-term memory system subserving the acquisition and retention of skills (’how to’ knowledge) and habits, specifically, the repetition-dependent, implicit knowledge of the structure of recurring experiences (Brown & Robertson, 2007; Cohen & Squire, 1980). The acquisition of new motor skills (for example, handwriting) is typically cited to demonstrate learning that is supported by the procedural memory system. Ullman (2004) highlighted the fact that the procedural memory system is involved in the acquisition of language skills and habits, such as our implicit knowledge of language rules, in addition to the acquisition of new motor skills. Tomblin, Mainela-Arnold, and Zhang (2007) recently studied the procedural learning of a sequence among adolescents diagnosed with specific LI in kindergarten, using the serial reaction time (SRT, Nissen & Bullemer, 1987) task. These authors observed that the learning curve of the SRT task consisted of a period of slowed responses prior to the onset of rapid learning. Lum, Gelgec, and Conti-Ramsden (2010) studied the SRT task in 7- and 8-year-old with and without LI. Their findings indicated lower accuracy and slower performance for children with LI. Observation of the reaction time learning curve presented therein verifies the later onset of rapid learning by children with LI. It is not clear, however, whether these results are specific to sequence learning, and whether deficient consolidation processes exist in addition to slower task performance. For example, Vicari et al. (2005) tested 16 school-age children with DD and matched typical readers on the SRT and on the mirror drawing tasks. The mirror drawing task is a procedural learning task that requires the establishment of fast and repetitive production of visuospatial stimuli but no acquisition of sequences. The participant is asked to repetitively trace a shape (e.g., star) through a mirror that inverts the image. Participants were trained on the mirror-drawing task, and memory consolidation was tested 24 h post-training session. Vicari et al. (2005) demonstrated that children with DD have lower accuracy and slower performance on the SRT task. Furthermore, although these children performed similarly to normal readers on the training phase of the mirror drawing task, they performed significantly less well on the retention of task, showing impaired consolidation processes of newly acquired motor skills. The current experiment was designed to study the time-course of learning a grapho-motor skill, the production of an invented 2-segment letter, in preschool children with LI and age-matched peers with comparable visual-motor integration skills. The children practiced production on day 1, and were tested 24 h and 2 weeks post-practice day. The invented letter task is a dot connecting task, and requires the establishment of fast and repetitive production of visuospatial stimuli but no acquisition of sequences. The task was developed to study skill acquisition and long-term retention in preschool children: (a) because typical skill learning tasks were found to be too difficult for young children (e.g., Wilhelm, Diekelmann, & Born, 2008), and (b) because of its direct relevance to the development of grapho-motor skills, a central skill in young children’s everyday life. Invented letter writing (Longcamp, Anton, Roth, & Velay, 2003, 2005a), grapho-motor mirror drawing tasks (Sosnik, Hauptman, Karni, & Flash, 2004; Vicari et al., 2005), circle drawing (Vinter & Detable, 2008; Vinter & Perruchet, 2000) as well as real letter writing (Adi-Japha et al., 2007; Adi-Japha & Freeman, 2000, 2001; Balas, Nester, Giladi, & Karni, 2007; Dorfberger, Adi-Japha, & Karni, 2009; James, 2010; James & Gauthier, 2006) have been used extensively in both behavioral and brain imaging experiments (e.g., James, 2010; Longcamp et al., 2008) for studying the effect of training on letter-form recognition and grapho-motor performance. Grapho-motor activity, whether tested by tracing figures (Estil et al., 2003), design copying (Marton, 2008), or handwriting fluency (Dockrell, Lindsay, Connelly, & Mackie, 2007), was found to be impaired in children with LI. Because consolidation and retention in the long-term memory of new skills is training-dependent (Hauptman, Reinhart, Brandt, & Karni, 2005; i.e., a minimal number of task repetitions during training may be necessary to trigger delayed consolidation gains), we ensured a similar level of visual-motor integration between children with LI and their peers. Studies have indicated that of all perceptual motor skills, visual-motor integration correlates most with handwriting performance (Daly, Kelley, & Krauss, 2003). In the present study, visual-motor integration was assessed using a copy-a-design paradigm, a paradigm that has been shown to be predictive of later school achievements (Grissmer et al., 2010). We assumed that similar visual-motor integration skills between groups would suffice to ensure a similar baseline. If children with LI would show a slower rate of task acquisition during the practice phase (Lum et al., 2010; Tomblin et al., 2007) or would fail to show consolidation gains 24 h post-practice, this would support the hypothesis of atypical procedural learning in LI (Ullman & Pierpont, 2005).
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2. Methods 2.1. Participants All 32 Israeli kindergarten children who participated in this study spoke Hebrew as their first language and used their right hand when drawing. Participating children were recruited from kindergartens in a central middle-high socioeconomic status (SES) city in Israel. Sixteen children with LI (4 girls) aged between 64 and 75 months were recruited from language kindergartens. These children were admitted to the kindergarten based on significant primary language impairment, normal nonverbal intelligence and sound adaptive behavior skills. The placement committee (comprised of the special education kindergarten district supervisor, municipal kindergarten psychologist, and special education therapists) assesses eligibility based on standardized cognitive assessments, speech-language pathologist referral, and information from previous kindergarten teachers and caregivers. All children referred to the placement committee are administered the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) adapted to Hebrew (Liblich, 1979). Children are referred to the placement committee as having a language disorder based on a failure on at least two language tests that are used in clinical practice in Israel, in the presence of normal performance IQ (Friedmann & Novogrodsky, 2004). After receiving Ministry of Education approval for the experimental procedure, parental informed consent forms were sent to parents of children who were identified by kindergarten teachers as having normal hearing, no additional communication disorders, no formal diagnosis or signs of attention deficit disorder, and do not regularly take any medication. Sixteen children with typical development (4 girls) matched by age and raw scores on a visual-motor integration (VMI) test were recruited from two kindergartens in the same city to serve as a comparison group. All children with LI scored more than a standard deviation below the mean of their age (and VMI) matched peers on the WPPSI vocabulary subtest (group difference of 1.5 SD on the standardized score). A standardized score of 75 or higher (i.e., above the 5th percentile) in the VMI test comprised an inclusion criterion for all participants. This criterion is based on a recent large-scale study showing that performance below the 5th percentile is appropriate for the definition of severe motor impairment which impacts children’s daily life (Lingam, Hunt, Golding, Jongmans, & Emond, 2009). All children scored 88 or more on the ‘‘draw a man test’’ for intellectual maturity (Harris, 1963, see details below; M = 97.68, SD = 8.93; M = 99.38, SD = 5.83, for children with LI and the comparison group, respectively, t(30) = .60, n.s). 2.2. Measures 2.2.1. Language tests All children were tested for receptive vocabulary using the Peabody Picture Vocabulary Test III (PPVT-III, Dunn & Dunn, 1997). Expressive vocabulary was assessed using the vocabulary subtest of the WPPSI adapted to Hebrew (Liblich, 1979). 2.2.1.1. PPVT-III. The children were tested using an expert translation of the PPVT-IIIB developed at Bar-Ilan University (AdiJapha, Berberich-Artzi, & Libnawi, 2010). In this test, the children were requested to point to a picture (one of 4 presented) that matches a word the examiner said. Testing continued until the child made 8 errors out of a block of 12 trials. Raw scores are reported. 2.2.1.2. WPPSI vocabulary subtest. In this test the children were requested to define words that the examiner read. Testing continued until the child made 5 consecutive errors. The mean standardized score is 10, and the standard deviation is 3. 2.2.2. Control test All children were tested on the Draw-a-man test (Harris, 1963), used here as a nonverbal intelligence test, to ensure a similar intellectual maturity level in the two groups, and on the Beery–Buktenica developmental test of Visual-Motor Integration (Beery-VMI) (Beery, Buktenica, & Berry, 2006) which was used to assess the extent to which the participants could integrate their visual and grapho-motor abilities. 2.2.2.1. Draw-a-man test. The developmental progression of children’s human figure drawings has been found to be sufficiently standard to allow estimates of intellectual maturity (Goodenough, 1926; Harris, 1963; Khaleefa, Abdelwahid, Abdulradi, & Lynn, 2008; Koppitz, 1968; Naglieri, 1988; Sharma, 2004). The test was used here to show that children’s graphic production does not indicate risk for general intellectual functioning. 2.2.2.2. VMI test. This test contains a sequence of 27 geometric forms of increasing complexity ranging from a simple vertical line to a complex three-dimensional star. The children were asked to copy each item as accurately as possible. Testing continued until the child made 3 consecutive errors. 2.2.3. Memory span tests The number recall and the hand movement measures from the sequential subtests of the Kaufman Assessment Battery for Children (K-ABC, Kaufman & Kaufman, 1983), adapted to Hebrew (Phizer, Shimborsky, Walf, & Hazani, 1995), were used to assess the short-term memory span.
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2.2.3.1. Number recall. The experimenter read a random string of digits of varying lengths (2–7 digits) out loud. The children were asked to repeat the string in the same order. Testing continued until the child made 3 consecutive errors. 2.2.3.2. Hand movement test. The children were presented with a random sequence of movements (palm down, fist, and side) of varying lengths (2–5 movements) and were requested to imitate the movements. Testing continued until the child made 3 consecutive errors. 2.2.4. The invented letter task The invented letter task was used in order to study the time-dependent course of motor skill acquisition. The task consists of point-to-point planar movements, and does not require memory load because the visual stimuli and direction of movement are available to the participants throughout the task. The current task was adjusted in difficulty to previously used letter learning tasks in kindergarten children (e.g., Longcamp, Zerbato-Poudou, & Velay, 2005b). In the invented letter task, children are asked to connect three encircled dots with lines (Fig. 1A: A ! B ! C, segment length 1.2 cm, circle diameter 2 mm) to form an invented letter. Movement progress was from right to left (as in Hebrew writing). Each experimental block was comprised of 3 rows of 5 dot-to-dot shapes that they should connect (Fig. 1B). The experimenter (second author of the paper, O.S.) explained the task to the children, and asked them to complete the task as rapidly and accurately as possible. The children were given one practice line in a paced manner at the beginning of each of the three experimental days. The experiment was held on two successive days (days 1 and 2), and long-term retention (retention session) was tested on a third day (day 3), two weeks later. Day 1 included training on 12 experimental blocks. On days 2 (consolidation session) and 3 (retention session) the children were tested during one experimental session consisting of 4 blocks. On all testing days the blocks were separated by a minimum of 15 s and up to a 30 s break. The experimental task was performed by the children on half of an A4 sheet of paper, using a HB pencil. After completion of each experimental block, the experimenter placed an identical sheet of paper in front of the child, for completion. The same task was repeated for the experimental sessions during the three intervals. No feedback was provided on any performance measure, only general encouragement (‘‘you are doing fine’’; ‘‘pay attention to the task’’; ‘‘remember to be as quick and accurate as possible!’’). The children completed the 12 experimental blocks on day 1 within 20 min. The 4 consolidation and retention blocks were completed within 5 min. 2.3. Statistical analysis Three experimental sessions were defined on day 1: pre-training (blocks 1–4), training (blocks 5–8) and post-training (blocks 9–12), in order to enable comparison between the current experimental design and other studies of skill acquisition (Dorfberger et al., 2007; Wilhelm et al., 2008), as well as to allow for comparison between day 1 and days 2 and 3. Days 2 and 3 consisted of one experimental session of 4 blocks. We chose 4 blocks as an experimental unit, similarly to other studies (Dorfberger et al., 2007; Wilhelm et al., 2008), in order to minimize measurement noise due to an erroneous block. Two measures were calculated to evaluate performance: speed of performance assessed as the time of completing an experimental block, and accuracy assessed as the average number of lines drawn within the circled area per block. Four testing sessions across the two week-period were used in the analysis: (a) Pre-training session (blocks 1–4 on day 1); (b) Post-training session (blocks 9–12 on day 1). (c) Consolidation session (4 blocks) assessed on day 2, 24 h post-training; and (d) Retention session (4 blocks) assessed two weeks following day 1. Speed and accuracy of performance were analyzed separately across the two week-period using: (a) a 4 (Session = pre-training; post-training; 24-h post-training; 2-weeks posttraining) 4 (Blocks) 2 (Group = comparison; SLI) repeated measures analysis of variance; or (b) within each of the three
Fig. 1. The ‘‘invented letter’’ stimuli. (A) A single stimulus. (B) One of the three rows of stimuli. The three rows constitute an experimental block.
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learning phases: training phase (pre-training vs. post-training), consolidation phase (post-vs. 2-weeks post-training) 4 (Blocks) 2 (Group = comparison; SLI). 3. Results Table 1 provides descriptive data of the participants. It can be seen that the participants in the two groups were comparable on the raw scores of the motor Beery-VMI tests. The LI group scored lower on the PPVT-III, the vocabulary subtest of the WPPSI and the number recall test. The latter is also considered a short-term verbal memory test (Gray, 2006). 3.1. The invented letter task 3.1.1. Performance time analysis The average block time in the 20 experimental blocks is shown in Fig. 2A. A Kolmogorov–Smirnoff test applied to block performance times did not reveal deviations from the normal distribution. A 2 (group = comparison, LI) 4 (session = pretraining, post-training, 24 h post-training, 2 weeks post-training) 4 (blocks per session) analysis of variance (ANOVA) for repeated measures indicated a main effect of group (F(1, 30) = 4.23, p < .05, h2p ¼ :13), a main effect of session (F(3, 90) = 21.09, p < .001, h2p ¼ :43), a main effect of block (F(3, 90) = 3.95, p < .05, h2p ¼ :12), and a significant group session block interaction term (F(9, 270) = 1.95, p < .05, h2p ¼ :07). As can be seen in the figure, the two groups displayed different learning curves in terms of performance time. Although children with LI were slower in all phases, a significant difference emerged only 24 h post-training (F(1, 30) = 7.14, p < .05, h2p ¼ :19). In the post hoc analyses (presented below) we studied the source of the group session block interaction found for performance time by analyzing day 1 practice gains (post- vs. pre-training), consolidation phase gains (24 h post-training vs. post-training), and retention phase (2 weeks posttraining vs. 24 h post-training). 3.1.1.1. Day 1 training gains. A 2 (group = LI, comparison) 2 (session = pre-training, post-training) 4 (block) ANOVA for repeated measures applied to performance time data indicated a significant main effect for session (F(1, 30) = 30.48, p < .001, h2p ¼ :50) as well as a significant group session block interaction term (F(3, 90) = 3.34, p < .03, h2p ¼ :10), with no other main effects or interactions. Post hoc ANOVA of group x block analysis applied to the two sessions (pre- and post-training) indicated a significant interaction only for the pre-training session (F(3, 90) = 3.83, p < .02, h2p ¼ :11). The interaction term suggests a higher level of improvement during the 4 pre-training blocks in the comparison than in the group of participants with LI. When tested in each group, improvement throughout the first four blocks showed a trend towards improvement for the comparison group (F(3, 45) = 2.54, p < .07, h2p ¼ :14) and was not significant for children with LI (F(3, 45) = 1.54, p > .2). In order to gain a more complete view of the first day learning, we tested the difference in the linear slope across each of the 4-block day 1 segments: pre-training (blocks 1–4), training (blocks 5–8) and post-training (blocks 9–12) in each group. A typical learning curve should show a significant reduction in performance time at the pre-training, vs. a plateau at post-training (AdiJapha, Karni, Parnes, Loewenschuss, & Vakil, 2008; Hauptman et al., 2005; Korman et al., 2003). A 2 (group = LI, comparison) 3 (training segments slopes = pre-training slope, training slope, post-training slope) analysis of variance for repeated measures indicated a significant interaction term (F(2, 60) = 3.49, p < .04, h2p ¼ :10). Post hoc analysis revealed that the source of interaction was the difference in slopes between the pre-training and the training segments of the two groups (F(1, 30) = 4.12, p < .05, h2p ¼ :12): the linear slope of the 4 pre-training blocks (blocks 1–4) decreased only for the comparison group, indicating an improvement in performance time (t(15) = 2.98, p < .01). The linear slope of the 4 training blocks (blocks 5–8) decreased in both groups (t(15) = 2.40, 2.25, p < .03, .04, for children with LI and the comparison group, respectively). In both groups the slope of the 4 post-training blocks (blocks 9–12) did not indicate a significant deviation from zero, which is consistent with a plateau performance. These results suggest a later onset of learning in the group of children with LI. Previous research suggests that when a single learning process is at work, a power-law function can well reflect the group-averaged performance curve (Ashby, Ennis, & Spiering, 2007; Logan, 1988; Newell & Rosenbloom, 1981; Segalowitz & Table 1 Descriptive data of the two groups. Children with LI
Age (months) VMI (raw) PPVT (raw) WPPSI (stand.) Number recall (stand.) Hand movement test (stand.)
Comparison group
t
M
SD
M
SD
69.81 10.62 59.68 6.75 8.25 8.24
2.66 2.70 16.66 1.40 3.99 6.44
67.93 12.06 70.56 11.18 11.93 10.92
3.92 2.72 13.48 2.85 3.15 6.12
1.58 1.49 2.03* 4.84*** 2.61* 1.18
VMI = Beery-VMI raw scores; PPVT = Peabody Picture Vocabulary Test III; WPPSI = vocabulary subtest of the Wechsler Preschool and Primary Scale of Intelligence. * p < .05. *** p < .001.
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# On target shapes per block
Time per block (sec.)
A 60
Control LI
50 40 30
14
Pre
Post
24h-post
2wks-post
Post
24h-post
2wks-post
B
12 10 8
Pre
Fig. 2. Speed and accuracy data (mean and standard error) of the comparison group and of the group of children with LI at 4 time points (indicated by a lower bar): pre-training (pre, blocks 1–4 on day 1), post-training (post, blocks 9–12 on day 1), 24 h post-training (24 h-post), and 2 weeks post-training (2 wkspost). (A) Time per block. (B) Number of shapes in which the child’s pencil moved within the outer circle.
Segalowitz, 1993). A deviation from a power-law fit may reflect a transition between performance modes. The previous analyses suggest that a transition between performance modes occurred among participants with LI. Although the fit to a power-law was significant for both children with LI and the comparison group (R2 = .63, 90, p < .01, .001, for children with LI and comparison group, respectively), the Wald-Wolfowitz runs algorithm (Adi-Japha et al., 2008; Wagenmakers & Brown, 2007) that tests whether the residuals of the power-function fit are random by assessing the number of times their signs (positive or negative) alternate, demonstrated a significant deviation from randomness for the group of children with LI (Z = 1.96, p < .05). As of block 7 their performance was consistently below what could be expected based on a power-law function fit. Overall, the above analyses suggest that the onset of effective learning occurred later for children with LI (on average, as of block 7) than for children in the comparison group. 3.1.1.2. Consolidation gains. A 2 (group = LI, comparison) 2 (session = post-training, 24 h post-training) 4 (block) ANOVA for repeated measures applied to performance time data indicated a main effect of group (F(1, 30) = 5.05, p < .05, h2p ¼ :14) and a significant group x session interaction (F(1, 30) = 4.18, p < .05, h2p ¼ :12). The source of the interaction was the improvement in performance time made by the comparison group between the post-training and 24 h post-training sessions (F(1, 15) = 30.31, p < .001, h2p ¼ :66), whereas the performance time of the LI group did not reveal a significant change. While 15/16 participants in the comparison group improved their performance between day 1 and 2, only 8/16 participants in the LI group did so (x2(1) = 7.57, p < .01). A group block analysis of the 24 h post-training session indicated a significant difference between the two groups (F(1, 30) = 7.14, p < .02, h2p ¼ :19) in favor of the comparison group. In contrast, the posttraining session analysis did not yield any significant effects. 3.1.1.3. Retention phase. A 2 (group = LI, comparison) 2 (session = 24 h post-, 2 weeks post-training) 4 (block) ANOVA applied to performance time data showed a block main effect (F(3, 90) = 4.23, p < .01, h2p ¼ :13) indicating improvement with blocks, and a significant group x session interaction (F(1, 30) = 7.96, p < .01, h2p ¼ :22). The source of the interaction was the improvement in performance time made by the LI group between the 24 h post-training and 2 weeks post-training sessions (F(1, 15) = 6.70, p < .03, h2p ¼ :30), whereas performance time of the comparison group did not reveal a significant change. In spite of their improvement, performance speed of children with LI 2 weeks post-training was at its post-training level (F(1, 15) = 1.31, p > .2), while for the comparisons it was significantly better than post-training performance (F(1, 15) = 6.56, p < .03, h2p ¼ :30). A group block analysis of the 2 weeks post-training session showed a significant block effect (F(3, 90) = 4.42, p < .01, h2p ¼ :13), indicating improvement between blocks, with no group main effects. 3.1.2. Analysis of accuracy data The average accuracy in the 20 experimental blocks is shown in Fig. 2B. A similar 2 (group = LI, comparison) 4 (session = pre-training, post-training, 24 h post-training, 2 weeks post-training) 4 (block) ANOVA for repeated measures applied to accuracy data indicated no significant main effects or interactions, suggesting that accuracy level was equal across groups and was maintained throughout the experimental period. Although children with LI were more accurate than the comparison group at all but two task blocks (Fig. 2B), this difference was not significant for any of the blocks (t(30) < 1.60, ps > .12), or overall (F(1, 30) = 2.40, p > .13; with less than one shape of 15, per block, difference) due to the large group variability (see Fig. 2B for mean and standard errors). It should be noted that, contrary to performance time differences
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between the groups, accuracy differences were consistent and not affected by training or time between experimental sessions. 3.1.3. Speed accuracy trade-off Speed-accuracy trade-off was studied using correlation analyses between the gains in speed and accuracy within the three study phases (training, consolidation and retention). The analyses suggested that for the group of children with LI, improvement in speed (i.e., reduction in performance time) was accompanied by reduction in accuracy in the training (from pre- to post-training, r = .62, p < .02) as well as in the retention phase (from 24 h post- to 2 weeks post-training, r = .61, p < .02).
4. Discussion Our findings indicate that when given a grapho-motor learning task, kindergarten children with LI presented an atypical learning curve, significantly differing from the comparison group in the practice phase, and in the post-training memory consolidation phase. Given the same training experience, children with LI showed a late onset of rapid learning (Tomblin et al., 2007). Twenty-four hours post-training only the comparison group showed delayed gains in speed of performance which were retained 2 weeks post-training. Children with LI gained in speed from pre- to post-training, as well as from 24 h post- to 2 weeks post-training, but at a cost in accuracy. Although at 2 weeks post-training they closed the gap in performance speed, they did not perform significantly better than their day 1 post-training level of performance. The matching procedure used in this study suggests that group differences cannot be explained by grapho-motor performance per se, as indicated by the Beery VMI scores. It should be noted, however, that the Beery-VMI test only measures accuracy of performance, and that the sample was small. This study is correlational in nature, and other factors not assessed here may explain the reported group differences. Furthermore, although the children with LI in this sample were not diagnosed as having other developmental deficits, these may be diagnosed at a later age. Group learning curves for a variety of tasks, with averaging across individual participants and across blocks of trials, are often characterized by negatively accelerated, gradually improving performance, typically characterized by a power-law (Ashby et al., 2007; Adi-Japha et al., 2008; Logan, 1988; Newell & Rosenbloom, 1981; Segalowitz & Segalowitz, 1993). However, performance of children with LI significantly deviated from the expected power-law learning curve. The comparison group showed an improvement in performance during the first four blocks of day 1, whereas children with LI showed improvement only after block 5 (with significant positive slope of gains in speed from blocks 5–9). These results add to the results of Tomblin et al. (2007) and of Lum et al. (2010), who reported a within-session sequence learning deficit in children with LI using the SRT task. Furthermore, Tomblin et al. (2007), who studied adolescents who were diagnosed with LI in kindergarten, reported late initiation of learning in the SRT task. However, possibly because of task complexity, participants with LI showed no evidence of an asymptote by the last trial block of the SRT task. In the current study, the simplicity of the task enabled participants with LI to set into an asymptote by the end of training in spite of late initiation of learning. These results suggest that children with LI are slower in forming motor patterns. Only the comparison group improved between day 1 and day 2, showing the expected delayed consolidation gains in speed of performance. By 24 h post-training, the speed of performance of the comparison group was significantly better than that of children with LI. Vicari et al. (2005) studied skill acquisition in school-age children with DD using the mirror drawing task. Although the dyslexic children and the comparison group performed similarly on the first day of training, the former were significantly slower than the normal readers 24 h post-training. These results are similar to the results of the current study and may suggest a mechanism of impaired procedural learning in both developmental disorders, although its origin may differ between these two etiologies. An atypical procedural memory system was suggested (Nicolson & Fawcett, 2007) as being involved in other developmental disorders, for example in ADHD (Adi-Japha et al., 2011). Children with ADHD are known to have impaired grapho-motor performance (Adi-Japha et al., 2007; Barkley, 1998). Children with LI significantly improved their performance from the 24 h post-training session to the 2 weeks posttraining session. This result was not expected, and may have occurred because the 24 h post-training session added to their training on the task. In spite of this improvement, their performance speed at 2 weeks post-training was not significantly better than their post-training performance speed. This result suggests that children with LI may require more training (Law, Rush, Schoon, & Parsons, 2009) or perhaps need more off-line time (or both) to show delayed gains. It may be hypothesized that retesting their abilities even later, possibly following some additional training, may demonstrate further improvement. High fluency and high accuracy are a hallmark of skilled performance (Anderson, 1982; Logan, 1988). Gains in speed of performance with no reduction, and sometimes with a concurrent increase in accuracy have been shown to evolve from practice in many laboratory tasks, in which perceptual, motor and cognitive skills were learned (Adi-Japha et al., 2011; AriEven Roth, Kishon-Rabin, Hildesheimer, & Karni, 2005; Ferman, Olshtain, Schechtman, & Karni, 2009; Karni et al., 1995; Karni & Sagi, 1993; Korman et al., 2003). Gains in speed in dot-to-dot grapho-motor learning tasks were found to evolve while accuracy at mid-dots was maintained (Sosnik et al., 2004). The current results show that while there was an improvement in speed with no reduction in accuracy during the training in the comparison group, in the SLI group both the expression of gains in speed during the training and at the retention interval was accompanied by a decrease in accuracy. A fast and inaccurate response style is one of the most salient features of ADHD (Adi-Japha et al., 2007, 2011; Eliasson, Rosblad, &
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Forssberg, 2004). Possibly, these results should be interpreted in light of the co-occurrence of LI with ADHD (Cardy, Tannock, Johnson, & Johnson, 2010; Love & Thompson, 1988), commonly not diagnosed before 7 years of age. The causes and biological basis of LI are poorly understood (Webster & Shevell, 2004). Although it is clear that our study does not solve the current debate about the underlying nature of SLI, it contributes new data to existing knowledge and broadens our understanding of the SLI phenotype. Specifically, the results of the current study corroborate the hypothesis of a typical procedural memory system in children with LI. The current results suggest that assessment batteries should incorporate assessment of motor skill learning as well as language in order to identify learning, rather than performance, deficits. 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