Understanding of Syntax by Children With Down Syndrome

Abstract

Frizelle, P., Thompson, P. A., Duta, M., & Bishop, D. V. M. (2019). The understanding of complex syntax in children with Down syndrome. Wellcome Open Research, 3, Article 140

The majority of individuals with Down Syndrome (DS) have a moderate intellectual disability (Chapman & Hesketh, 2001), although their IQ scores can range from the severe to the average range (Roizen, 2007). Language difficulties in children with DS are well documented, particularly those affecting vocabulary, phonology, morphology, and simple sentence structures (Eadie et al., 2002; Laws & Bishop, 2003). However, information regarding these children’s understanding of complex syntax is limited. In addition, although children with DS have increased risk of a number of difficulties likely to influence their language development (e.g., limited cognitive ability, hearing level, memory skills), the relationship between these factors and language competence is not straightforward and has never been investigated in relation to the complex syntactic abilities. Based on previous research with children with DS, the researchers made the following hypotheses for this study:

Hypothesis 1: Individuals with DS will be able to understand a range of the complex sentences tested, although considerable individual variation is expected.

Hypothesis 2: Those with DS will perform more poorly overall than typically developing (TD) controls but at a similar level to those with cognitive impairment (CI) of unknown origin.

Hypothesis 3: Children will have greater difficulty understanding comparable syntactic constructions on a multiple-choice test that requires them to hold a sentence and compare it with four pictures than on an animation task in which they determine whether a sentence matches or does not match the animation.

Hypothesis 4: Cognitive ability, verbal memory, working memory and hearing level will predict performance in the DS group.

Hypothesis 5: Cognitive, verbal, and working memory abilities will account for more variance on the multiple choice than on the animation task.

Participants

A total of 33 boys with DS (M age = 9½ years) participated. Two comparison groups of boys also participated: 32 children (M age = 10 years) with CI of unknown etiology and 33 TD children (M age = 6½ years). Children were matched on non-verbal mental age. To avoid floor effects, only those with a non-verbal mental age of 3½ years and above on the Leiter International Performance Scale, 3rd Edition (Leiter-3; Roid et al., 2013) were included, and children were required to be capable of producing three-word utterances at a minimum.

Procedures

Assessments included the following:

Leiter-3

This is a non-verbal test of cognitive ability involving four core subtests: figure ground, form completion, classification, and sequential order. The test is designed to require no language for administration.

Memory Assessments

These included versions of the digit recall and backward digit recall subtests from the Working Memory Test Battery for Children (WMTB-C; Pickering & Gathercole, 2001), adapted for delivery through a laptop. Digit recall involves immediately recalling a series of numbers in the order they were presented and is considered a measure of verbal short-term memory. Two measures were taken from each of the digit recall tasks: (a) the number of trials in which the participant successfully recalled all the items in their correct serial order (span), and (b) the number of trials in which the participant recalled all the items in each set presented, regardless of the order (accuracy) (this was done to avoid floor effects). Backward digit recall involves repeating a list of digits in reverse order and is regarded to be a measure of working memory, as it requires both the storage and processing of information.

Visuospatial memory was assessed using a version of the block recall test from the WMTB-C (Pickering & Gathercole, 2001). Participants were presented with an array of nine identical images (of a leaf) behind which there were cartoon monsters. Beginning with one and gradually increasing in number, monsters were revealed for a period of 4 s. The participant was required to recall the location of the monsters by touching the appropriate leaves on the screen. Again two measures were taken for this task: the number of trials in which the child successfully recalled the monsters in the correct order presented (span) and the number of trials in which the child recalled all the monsters in each set presented regardless of the order (accuracy).

Test for Reception of Grammar (TROG-2)

TROG-2 (Bishop, 2003) is a multiple-choice sentence picture-matching task. Participants listened to a target word or sentence and from a choice of four and were required to identify the corresponding picture. Syntactically simple sentences were presented first followed by those that were more complex.

TECS-E Complex Syntax Comprehension Task

This was a newly devised sentence-verification task using animations presented on a tablet. Participants were shown 114 test animations in total, each with an accompanying auditory test sentence. The animations represented one of five types of relative clauses, four types of sentential complements, and four types of adverbial clauses. Children were asked if what was shown in the animation matched the sentence they heard and to respond by touching either the smiley or sad face. Examples of correct and non-match relative clause items are available on YouTube at https://youtu.be/d3dz_m8zTvc and https://youtu.be/FMxYzSyCs34, respectively. Examples of correct and non-match complement clause animations are available at https://youtu.be/OM27lMM4zPs and https://youtu.be/yPBQP14VjFA, respectively. Examples of correct and non-match adverbial clauses are available at https://youtu.be/ILsCSUriGRU and https://youtu.be/Cd-EBpCtzZw, respectively. Table 1 displays examples of each type of clause.

Table 1.

Syntactic Clause Types.

Syntactic type	Example
	Relative clauses
	Complement clauses
Subject intransitive	She pointed to the man that was reading
Subject transitive	He saw the girl that picked the flowers
Object	The girl found the shoe he lost
Oblique	The girl cleaned the teddy he played with
Indirect object	He kissed the woman he bought the shoes for
Think	She thinks the cat is in the basket
Know	He knows the girl threw the ball
Pretend	The boy is pretending he is brushing his teeth
Wish	The boy wishes he could climb the tree
	Adverbial clauses
Before	Before the girl fell from the tree she drank the juice
After	The boy ate the cookie after he drank the milk
If	If the gate was open the horse could walk away
Because	The baby cried because she spilt her milk

Results

1. Prediction : Children with DS would be able to perform at or above chance level on complex sentences when assessed using the sentence-verification task (TECS-E), designed to minimize extra linguistic and cognitive demands.

Results: Only 39% of the children with DS performed at a level above chance. This was in contrast to the two control groups, the majority of whom performed above chance level (74%) in the CI group and all of whom performed above chance level in the TD group.

2. Prediction : Children with DS would perform at a similar level on TECS-E to those with CI of unknown etiology but at a lower level to those with typical development (matched on non-verbal mental age).

Results: Intellectually impaired children achieved an average score of 25.12 points less than the TD children, despite being matched on non-verbal mental age. Children with DS achieved an average score of 10.25 less than the CI group showing a disproportionate difficulty in their ability to understand complex sentences.

3. Prediction : Children with DS would have greater difficulty understanding comparable constructions on the TROG-2 (a multiple-choice comprehension task) than on TECS-E.

Results : To compare the two testing methods fairly, the researchers adopted a stringent scoring of the TECS-E, where a pass was credited for perfect performance (8/8 two-choice items correct); the probability of achieving 8/8 by chance is the same as for getting all 4 four-choice items correct on TROG-2. No child from the DS or CI samples achieved this level of performance, and only five children (15%) from the TD group did this well. In contrast, 26/33 (79%) of the TD children, 13/32 (40%) of the CI children, and 6/33 (18%) of the DS children had perfect performance on the intransitive subject relatives on TECS-E. This is in line with our prediction that more children would pass these constructions on the sentence-verification task than on TROG-2.

4. Prediction : The ability of children with DS to understand complex sentences would be explicable in terms of their deficits in verbal short-term memory, working memory, and hearing level.

Results : Children’s performance on TECS-E was not completely explained by their poor memory skills; DS status makes an independent contribution to children’s performance on the task.

5. Prediction : Cognitive and memory variables would account for more of the variance in children’s performance on the multiple-choice comprehension task (TROG-2) than on TECS-E, given the additional executive demands of multiple-choice comprehension tasks.

Results : In accord with prediction all three groups performed best on relative clauses. Children with typical development performed near ceiling on all relative clause types. With the exception of subject intransitive relatives, children with DS had significant difficulty understanding all other relative clause types. Their performance on adverbial and complement clauses was at floor (ranging from 0% to 12% of children passing these constructions). Children with CI of unknown etiology also found subject intransitive relatives the least difficult construction to understand and their relative clause performance showed the following pattern: subject intrans > subject transitive = indirect object > object = oblique. In relation to adverbial clauses, children with CI performed best on the causal adverbial because and found the conditional adverbial if the most difficult to understand. TD children had greatest understanding of before temporal and because causal constructions, with the conditional if causing difficulty for 76% of these children. For complement clauses, children with CI showed the strongest understanding of pretend constructions, with think causing the greatest difficulty. For TD children, the complement clause constructions wish and pretend presented the least difficulty and think constructions were most difficult for children to understand.

Discussion

Although we might expect that cognitive ability is a core factor in explaining receptive language differences between those with DS and other groups, the literature is not consistent in this regard. Several studies suggest that the receptive vocabulary of those with DS is in keeping with that of cognitively matched children with typical development (Chapman et al., 1991; Laws & Bishop, 2003), while other studies suggest a lower performance from those with DS (Caselli et al., 2008; Hick et al., 2005). The literature regarding syntactic comprehension appears to more consistently show that those with DS have a lower than expected understanding of syntax relative to their non-verbal cognitive skills (Abbeduto et al., 2003; Chapman et al., 1991; Joffe & Varlokosta, 2009; Laws & Bishop, 2003).

A number of studies have shown that expressive grammar in people with DS continues to develop throughout adolescence and possibly into adulthood (Chapman et al., 2002; Laws & Gunn, 2004), whereas those exploring syntactic comprehension report mixed findings; many suggesting that syntactic comprehension is likely to reach a plateau in late adolescence or even to decline with age (Chapman et al., 2002). Although not specific to complex syntax, Witecy and Penke (2017) found that receptive syntactic growth in those with DS continues through childhood into adolescence. Therefore, while these findings suggest that children with DS have significant difficulty understanding complex sentences at this point in their development (with an average mental age of 6;7 years), they may have the potential to understand them as they progress into teenage and adolescent years, with the corresponding increase in their cognitive functioning. Considering the results of this research, speech–language pathologists should target syntactic development when working with persons with DS, and ideally such interventions should continue through adolescence.

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