Prosodic deficits in children with Down syndrome

Journal of Neurolinguistics 24 (2011) 145–155

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Prosodic deficits in children with Down syndrome Vesna Stojanovik* School of Psychology and Clinical Language Sciences, University of Reading, Earley Gate, Reading RG6 6AL, UK

a r t i c l e i n f o

a b s t r a c t

Article history: Received 26 October 2009 Received in revised form 22 January 2010 Accepted 24 January 2010

The aim of this study was to investigate comprehension and production of prosody in a group of nine children with Down syndrome (DS) and to compare their performance to two control groups: one matched to the DS group on chronological age (CA group) and the other one matched to the DS group on receptive language and non-verbal abilities (MA group). Prosody was assessed using the computerised battery ‘‘Profiling Elements of Prosody for Speech and Communication’’ which assesses both prosody form and prosody function. The results showed that the DS group scored significantly lower than the CA matched group on all aspects of prosody under investigation. The DS group scored significantly lower than the MA group on the production of affect and on the production of pre-final narrow focus, and on all four tasks assessing prosody form. The DS group scored, on the whole, significantly higher on the comprehension prosody tasks than on the production ones. This pattern mirrored the one found in the general DS language profile which is characterised with strengths in language comprehension and weaknesses in language production. Interestingly, the receptive language abilities of the DS group did not seem to be related to their prosodic abilities, suggesting that prosody may be an independent cognitive domain. Ó 2010 Elsevier Ltd. All rights reserved.

Keywords: Prosody Down syndrome Children Deficits Language

Susan Edwards’s early research interests were within the field of atypical language development and in particular, language in infants with learning difficulties, including a child with Down syndrome (DS) (Edwards, 1990). This was the first study, to my knowledge, to investigate the use of prosody in a child with DS and to provide a detailed analysis of the types of tone units and prosodic contrasts used.

* Tel.: þ44 0118 378 7456. E-mail address: [email protected] 0911-6044/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jneuroling.2010.01.004

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Another very important aspect of Susan Edwards’ work is her theoretical contribution to the field of clinical linguistics. Her work, addressing both developmental and acquired language disorders, has contributed to debates on whether the brain has dedicated neural mechanisms for different cognitive functions from birth. This is relevant to the current paper because evidence from atypical populations, such as individuals with DS, is often referred to when arguments are made with regard to this issue. To celebrate Susan Edwards’s work, this paper will focus on prosody in children with DS and discuss the findings within current theoretical frameworks. 1. Background DS is a genetic disorder resulting from a genetic error in that the embryo receives three chromosomes 21, hence the often used term for DS trisomy 21. The majority of cases with DS (about 97%) results from this type of genetic error. There are also two other types of genetic error (mosaicism and translocation) that result in DS (Rondal & Edwards, 1997). Trisomy 21 mosaicism occurs due to a genetic error which leads to the embryo developing with a mosaic of normal cells containing 46 chromosomes and some cells which have three copies of chromosome 21. The third type of DS, called trisomy 21 translocation, occurs when the extra chromosomal material is a triplicate of chromosome 21 and also a part of another chromosome. DS is one of the most common causes of developmental delay and learning disabilities. Studies vary with regard to the incidence of DS occurring approximately in 1 in 800 live births (‘‘Downs syndrome, 2010’’: http://www.nhs.uk/conditions/downs-syndrome/Pages/Introduction.aspx). DS results in a number of physical and cognitive abnormalities, such as short stature, hypothyroidism, hypotonia, congenital heart disease and mild to moderate learning difficulties with an average IQ range between 40 and 60 (Prasher & Cunningham, 2001). One of the reasons for studying populations such as individuals with DS is because they provide a unique opportunity to investigate the relation between language, brain and specific genotypes. In typically developing children, language and other cognitive systems develop in a fairly integrated manner, which makes it difficult to tease apart individual components and processes (Reilly & Wulfeck, 2004). In individuals with developmental disorders, the genetic abnormalities constrain the developmental trajectory of different cognitive abilities (Karmiloff-Smith, 1998) which often results in a cognitive profile with relative strengths and weaknesses. Thus studies of distinct and well-defined atypical populations, such as individuals with DS, allow for the investigation of the dissociability of aspects of cognition and provide a window into the underlying architecture of cognitive organization. For example, despite the fact that both individuals with DS and those with Fragile X syndrome have comparable non-verbal IQs, marked differences have been reported with regard to their expressive morphosyntactic abilities, in that those with Fragile X syndrome tend to significantly outperform those with DS (Abbeduto et al., 2001). This would suggest that the acquisition of morpho-syntax may not be solely reliant upon non-verbal IQ and there are other cognitive factors that must play a significant role. Acquiring speech and language is a challenge for most individuals with DS and few individuals with DS ever attain full mastery of language. Although it has been noted that DS is more detrimental to speech and language than other types of learning difficulties (Dodd & Thompson, 2001; Fowler, Gelman, & Gleitman, 1994; Rondal, 1993), there has not been a lot of research on speech and language in DS compared to other disorders presenting with learning difficulties, such as for example, autism or Williams syndrome. Individuals with DS show an uneven cognitive profile with regard to their language abilities. Receptive vocabulary tends to be in line with general cognitive abilities, but morphosyntactic abilities are impaired (Chapman, Schwartz, & Kay-Raining Bird, 1991; Chapman, Seung, Schwartz, & Kay-Raining Bird, 1998; Fowler et al., 1994; Laws & Bishop, 2004; Miller, 1988). Some studies have also shown lower language than non-linguistic abilities in participants with DS (Chapman et al., 1998; Fowler, 1990; Fowler et al., 1994; Rondal & Comblain, 1996). Speech intelligibility is a problem for individuals with DS. It often results from omission or substitution of speech sounds (Chapman & Hesketh, 2001) or inconsistency of production of sounds (Dodd, 1976). It has been suggested by some that speech intelligibility and the speech errors made by individuals with DS may be associated with difficulties with identifying word and phrase boundaries, which are related to rhythm and prosody (Bray, Heselwood, & Crookston, 1995; Heselwood, Bray, &

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Crookston, 1995). Despite these observations, research so far has mainly focused on segmental phonology, with few studies on suprasegmental features. A study by Reilly, Klima, and Bellugi (1990) reported that adolescents with DS used less affective expressive prosody in a story telling task compared to adolescents with Williams syndrome but more in line with mental age matched participants. Perception of prosody was not investigated. Recently, Pettinato and Verhoeven (2009) investigated the processing of word stress in children and adolescents with DS and reported disrupted stress structure. More specifically, their results from a production and a comprehension task indicated that word stress and weak syllables found at the beginning of words are not adequately encoded in the phonological systems of individuals with DS. From a human communication point of view, being able to use prosody successfully and interpret the prosodic features of other people’s speech is essential for effective communication. Prosody can be used to express emotional states or attitudes (affect), to make specific words or syllables stand out in a stream of speech (focus), to discriminate grammatical units or, for example, disambiguate compound nouns from single nouns (chunking) and to regulate conversational behaviour (interaction) (Roach, 2000). From a theoretical point of view, it is important to study prosody because there is currently no consensus regarding the issue of whether prosody is independent of morphosyntactic, segmental phonological and general cognitive impairments (Wells & Peppe´, 2003). Research by Wells and Peppe´ (2003) showed that expressive and receptive language abilities and intonation performance in a group of children with speech and language impairments were not strongly related. Stojanovik, Setter, and van Ewijk also showed that expressive and receptive prosodic abilities are not related to language abilities in children with Williams syndrome. Such findings suggest that prosody may be relatively independent from other language abilities. On the other hand, Weinert (1992) argued that prosodic deficits may be associated with language deficits in German speaking children with Specific Language Impairment (SLI) because she found that they did not use prosodic cues when learning rules in a miniature language, or in repeating miniature language sentences. It could be the case, however, that children rely on prosody more in the earlier stages of language acquisition, but that in later childhood prosody becomes a more independent cognitive domain. These findings are directly relevant for the issue of whether there are dedicated neural mechanisms for specific cognitive functions (in this case prosody) in a developing cognitive system, although up to this point, there is no definitive answer. The aim of the current study is to investigate the comprehension and production of several aspects of prosody in a group of children with DS and to find out if receptive language skills may be related to their prosodic skills. The specific research questions to be addressed are: 1) How does the comprehension and production of intonation of children with DS compare to the intonation performance of typically developing children of a similar chronological age and typically developing children of similar non-verbal and receptive language skills? 2) Is there a difference between children with DS’s performance on production and comprehension of prosody? 3) Is the DS participants’ performance on production and comprehension of prosody related to their receptive language skills? 2. Method 2.1. Participants There were three groups of participants: a group of nine children with DS and two control groups of typically developing (TD) children: one matched to the DS group on non-verbal mental age (MA) and the other one matched to the DS group on chronological age (CA). All participants’ details are presented in Table 1. 2.1.1. Participants with DS Nine participants with DS were recruited through DownsEd International, UK. Their ages ranged from 8;03 to 12;05 (mean age: 9;09). They all had English as their first language, no diagnosis of autism, a hearing loss no greater than 55 db1 and they all had receptive language which was equivalent to age 4

1

Hearing loss is common in individuals with DS.

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Table 1 Participants’ details.

DS MA control CA control

Age

TROG (raw scores)

RCM (raw scores)

9;09 (sd 1;05) 5;05 (sd 1;01) 9;05 (sd1;02)

5 (sd 1) 6 (sd 2) 19 (sd 1)

15 (sd 3) 16 (sd 4) 33 (4)

DS – Down syndrome, MA – mental age, CA – chronological age; TROG – test for the reception of grammar; RCM – Ravens coloured matrices.

as assessed on the Test for the Reception of Grammar (TROG) (Bishop, 2003). This was to ensure that the children had good enough receptive language abilities to be able to understand the prosody tasks. 2.1.2. MA matched controls There was a group of eight typically developing participants aged between 4;02 and 5;07 (with a mean age of 5;05) recruited through primary schools in the Reading area who were matched to the DS group on non-verbal mental abilities as assessed on the Coloured Progressive Matrices (CPM) (Raven, 2003). There were no differences between the groups on their raw scores on the CPM (Mann– Whitney U ¼ 25.500, p ¼ .321). They were also matched to the DS group on receptive language skills as assessed on the TROG (Mann–Whitney U ¼ 24.000, p ¼ .277). 2.1.3. CA matched controls Eight typically developing children matched to the DS group on chronological age were recruited through local primary and secondary schools. Their ages ranged from 8 to 11 (with a mean age of 9;08). There were no differences between the groups on CA (Mann–Whitney U ¼ 35.000, p ¼ .963). 2.2. Materials Comprehension and expression of prosody was assessed using the computerised version of the Profiling Elements of Prosody for Speech and Communication (PEPS-C) by Peppe´, McCann, and Gibbon (2003). The assessment follows a psycholinguistic framework (Wells & Peppe´, 2001) and is based on an earlier manual version. The tasks are divided into form (bottom-up processing where no meaning is involved), which refers to auditory discrimination and voice skills required, and function (top-down processing which involves meaning), i.e. how communication is affected by prosody in speech. The battery consists of 12 tasks, 8 of which assess prosody function and 4 of which assess prosody form. The prosody function tasks are: turn-end, affect, chunking and focus. The function comprehension tasks require the participant to select the picture which best corresponds to the way a word or utterance is being said. In the function production tasks, the participant is required to use intonation in order to convey different meanings with the support of different pictures. The prosody form tasks involve same/different discrimination of prosodic variations (two tasks: short and long items), and each has comprehension (discrimination) and production (imitation) counterparts. In the comprehension tasks, the participant hears pairs of one or two syllable pitch patterns and is asked to say whether they were the same or different. The production form tasks require the participant to repeat either single words or phrases by using exactly the same intonation pattern as the one they heard on the computer. Each task consists of two practice items and 16 test items. The practice items ensure that the participant understands what he/she is required to do. A full description of each task is included in Appendix 1. 2.3. Procedure The participants were tested individually either in a quiet room at their school, or in their homes. A few children were tested in a dedicated laboratory at the University of Reading. A session lasted approximately 45–60 min. All the children were administered the TROG as a measure of receptive

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language abilities and the Coloured Progressive Matrices (RCM) (Raven, 2003) as a measure of general non-verbal cognitive abilities. Prior to administering the PEPS-C battery each child was asked to go through a picture naming task containing all the pictures which later appeared in the prosody tasks. This vocabulary check was needed in order to ensure that the children were familiar with the vocabulary items which were to appear in the prosody tasks. Tasks were presented in random order to different participants to ensure that there were no presentation order effects. All the production tasks were recorded directly onto the laptop as well as on a DAT recorder or on a minidisc as a backup. 2.4. Inter-rater reliability Eighty percent of the responses from the production tasks for all three groups of participants, having initially been rated by trained research assistants and a student who collected the data, were independently rated by another trained phonetician. There were two testers: one collected the data from the typically developing children and the other one collected the data for the children with DS. All the data were second rated by a trained phonetician who was not present at the data collection. Interrater agreement was calculated using kappa coefficient in order to account for chance agreement. Kappa inter-rater reliability coefficient was calculated on a random 20% of this material. This was highly significant (k ¼ .845; p < .001) which suggests a very high level of agreement between the raters. 3. Results The performance of the 3 groups of children on the function tasks of the PEPS-C battery is presented in Table 2. The scores are given in percentages correct, i.e. number of correct items out of number of scorable items. Number of correct responses in percentages rather than raw scores are given because for some of the production tasks it was possible for an item to be unscorable. For example, in the Turn-end production task, on some of the items the child had to say: ‘‘cabbage?’’ with rising intonation as if offering it to somebody but they actually said: ‘‘do you like cabbage?’’ Such an error does not necessarily signal that the child is unable to use the correct prosodic pattern per se, but it rather suggests that they produced an item which contained extra words in it and therefore could not be

Table 2 Raw scores in percentages (number correct/number scorable) on six FUNCTION PEPS-C tasks. AI

AO

FO

TI

59.7** 12.1 37.5 75

56*/** 29.5 14.3 100

57.6*** 13.4 56.3 100

92.5*** 8.1 68.7 100

68.8 19.8 37.5 87.5

97.4* 3.5 93.3 100

83.8 16.3 56.3 100

56.3 38.3 18.8 100

94.4*** 6.2 81.3 100

89** 12.8 62.5 100

97.7** 3.2 93.8 100

97.7*** 4.7 87.5 100

85.9*** 20.3 56.3 100

Group DS (n ¼ 9) Mean SD Min Max

63.2* 12.3 37.5 81.3

32.4*** 18.8 7.7 60

MA (n ¼ 8) Mean SD Min Max

80 21.8 43.8 93.8

CA (n ¼ 8) Mean SD Min Max

87.5* 19.5 43.8 100

FI

TO

38.3*** 9.4 26.7 53.9

PEPS-C ¼ Profiling Elements of Prosody for Speech and Communication; AI – affect input; AO – affect output; CI – chunking input; CI – chunking output; FI – focus input; FO – focus output; TI – turn-end input; TO – turn-end output; MA – controls matched on receptive language and non-verbal skills; CA – controls matched on chronological age. The differences between the DS and CA/MA groups are marked using stars: *significance at .05; **significance at .01 level; ***significance at .001 level. The significant differences are also marked in bold.

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scored. Thus it was deemed that reporting only the number of correct items out of possible items was not representative of the children’s prosodic abilities and percentage correct scores are reported. 3.1. Results from the FUNCTION tasks Results from the function tasks are presented in Table 2. A one-way ANOVA was carried out to investigate the main effect of group on the 6 different variables. Depending on whether the homogeneity of variance test was significant for a variable, posthoc Bonferroni comparisons (if variance was homogeneous) or Tamhane’s comparisons (if variance was non-homogeneous) were carried out in order to find out which groups different from each other. Six out of nine participants with DS did not seem to be able to reliably carry out the Chunking comprehension and production tasks. Therefore, these two tasks were excluded from the analysis for all the participants. As Table 2 shows, the DS group scored significantly lower on all the prosody tasks assessing prosody function than the CA matched control group. In general, the DS group scored lower than the MA group on all tasks, however, the difference between the two groups was statistically significant for only two tasks: the affect production task and the focus production task. We also carried out paired non-parametric tests to investigate whether there were significant differences between the comprehension and the production counterparts of each prosody function task. The DS group were significantly better at understanding of affect than expressing affect (Wilcoxon Z ¼ 2.666, p ¼ .008) and they were also significantly better at the turn-end comprehension task than at the production task (Wilcoxon Z ¼ 2.366, p ¼ .018). For the MA matched group, there was also a significant difference in their performance with regard to the turn-end task in that they performed better on the comprehension than on the production counterpart (Wilcoxon Z ¼ 2.117, p ¼ .034). The MA matched group was also significantly better at expressing focus than understanding it (Wilcoxon Z ¼ 2.023, p ¼ .043). No differences between the comprehension and production counterparts on any of the tasks were found for the CA group. 3.2. Results from the FORM tasks Table 3 shows the results from the prosody form tasks for the three groups of participants. As for the above analysis, One-way ANOVA was carried out to investigate the main effect of group on the 4 different variables. Depending on whether the homogeneity of variance test was significant for

Table 3 Raw scores in percentages (number correct/number scorable) on four FORM tasks. SD Group DS (n ¼ 9) Mean SD Minimum Maximum

52.8**/*** 9.9 37.50 68.75

SI

63.5*/*** 18.2 34.4 90.63

LD

LI

49.3*** 13.1 25 62.50

52.8*** 11.4 39.3 73.3

MA (n ¼ 8) Mean SD Minimum Maximum

79.7** 15.9 50 100

84.8* 14.7 53.1 96.9

88.8*** 12 68.8 100

86.2*** 7 75 96.9

CA (n ¼ 8) Mean SD Minimum Maximum

96.1*** 5.7 87.50 100

97.7*** 3.6 90.6 100

93.8*** 5.8 87.5 100

97.3*** 5.1 87.5 100

SD – short-item discrimination; SI – short-item imitation; LD – long-item discrimination; LI – long-item imitation. The differences between the DS and CA/MA groups are marked using stars: *significance at .05; **significance at .01 level; ***significance at .001 level. The significant differences are also marked in bold.

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a variable, posthoc Bonferroni comparisons (if variance was homogeneous) or Tamhane’s comparisons (if variance was non-homogeneous) were carried out in order to find out which groups different from each other. There was a main effect of group for all the tasks: Short-item comprehension (F ¼ 32.166, df ¼ 2, p ¼ .000); Short-item production (F ¼ 13.183, df ¼ 2, p ¼ .000); Long-item comprehension (F ¼ 42.329, df ¼ 2, p ¼ .000) and Long-item production (F ¼ 62.968, df ¼ 2, p ¼ .000). As Table 3 shows, the DS group was scored significantly lower than both groups of typically developing participants on all the prosody form tasks. There were no significant differences, however, between the comprehension and production counterparts for any of the tasks. In order to find out if level of linguistic performance may be related to performance on the understanding and production of prosody in children with DS, Spearman’s correlations were carried out only for the DS group. The only significant correlation was between the short-item discrimination task and the receptive language abilities as measured on the TROG (Spearman’s rho ¼ .859, p ¼ .003). We have shown in a previous study (Stojanovik, Setter, & van Ewijk, 2007) that in typically developing children, there is a correlational relationship between receptive language abilities and performance on the comprehension subparts of Chunking, Focus and Turn-end tasks and receptive language skills and performance on the production counterparts of Chunking and Short-item and Long-item imitation (i.e. production). 4. Discussion This paper set out to investigate how comprehension and production of prosody of children with DS compares to the comprehension and production of prosody of typically developing children of a similar chronological age and typically developing children of similar non-verbal and receptive language skills. It also aimed to find out whether there was a discrepancy between children with DS’s comprehension and production prosodic skills and whether receptive language skills of children with DS are linked to their performance on the prosodic tasks. This is the first study to my knowledge to address the issue of both prosody comprehension and production in children with DS. With regard to the first research question, the results from the PEPS-C battery showed that the DS group performed significantly lower than the participants of a similar chronological age on all the prosody tasks. This suggests that comprehension and production of prosody in children with DS is severely impaired relative to their chronological age and this holds not only when prosody is used for communication purposes, but also with regard to their ability to discriminate between different intonation patterns or imitate intonation. When compared to children who have similar receptive language abilities and similar non-verbal abilities, the children with DS showed a different pattern. Although their scores were, on the whole, lower than those of the MA matched controls, the children with DS performed only significantly worse than the MA group on two prosody function tasks (production of affect and focus) and all the prosody form tasks. Such findings suggest that children with DS have marked deficits relative to their non-verbal abilities and receptive language skills, when asked to use prosody to express affective states and when asked to use prosody in order to mark the most prominent word in an utterance. They also have marked deficits with regard to formal aspects of prosody in that they found it very difficult to distinguish between different prosodic patterns when no meaning was involved. The results also suggested a possible relative strength in the DS prosodic profile with regard to the interaction function of prosody, in that they did not perform significantly lower than the MA matched controls on the two tasks which assessed this prosodic function. However, this should be viewed with caution, especially with regard to the production counterpart of the task. Although there was no statistical difference between the DS and MA groups on the production Turn-end task, the DS group performed below chance (below 50% overall on the task), which means that they were unable to reliably use a fall or a rise in order to express offering an item or reading the item from a book. Thus this appears to be a false relative strength in absolute terms, however it is a relative strength given their level of cognitive ability. The second research question aimed to address possible discrepancies between comprehension and production prosodic skills in children with DS. Comparisons between comprehension and production of prosody showed some interesting patterns. The DS group was significantly better at the

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understanding of affect than being able to produce it, which suggests that the children with DS are better at perceiving the rise–fall/fall–rise dichotomy but are unable to produce these tones successfully. This finding is in line with those of Edwards (1990) of a single case study of a child who did not spontaneously use many fall–rise and rise–fall tones, which suggests that these may be particularly difficult for children with DS. The control groups in the current study did not show this pattern of asynchrony between expression and production of rise–fall/fall–rise, further suggesting that difficulties with the production of these two different tones often used for the expression of affect in English makes expression of affect difficult for people with DS and may be a candidate syndrome-specific characteristic. In fact, past research on children with Williams syndrome has shown that affect expression may be a specific relative strength of this population (Reilly et al., 1990; Stojanovik et al., 2007). However, data from other atypical populations, and especially other genetic syndromes, are needed before these possible syndrome-specific patterns are confirmed. The DS group were significantly better at understanding rise and fall as used for the purposes of interaction (asking a question as opposed to uttering a statement) than being able to express these. This pattern was also present in both control groups and was more prominent in the younger control group. There is no clear developmental picture about children’s use of intonation for the purposes of interaction (turn-end) (Wells, Peppe´, & Goulandris, 2004) and therefore we do not know exactly what to expect at which chronological age, however the fact that the DS group seem to mirror the pattern in the control groups suggests that this aspect of prosody perhaps develops similarly to what is observed in typically developing children. With regard to focus, the control groups, and in particular the younger control group, showed better performance on the production of focus than on comprehension. This is in line with what has been found before. Thus Cutler and Swinney (1987) have shown that children aged 3;0–5;11 can use accent placement to manipulate narrow focus in their own speech, however studies of comprehension have shown that some aspects of interaction between accent and focus may not be fully mastered by the age of ten (Cruttenden, 1985). The DS group did not show this pattern (i.e. better production than comprehension). In fact they scored marginally better on the comprehension counterpart of the task than on the production counterpart, which is the opposite pattern to that in the typical population. Overall, the DS group showed better comprehension than production prosodic skills and this was particularly obvious on the function tasks.2 This is in line with what has been widely reported with regard to their language skills in general, in that their language comprehension is relatively better than language production (Rondal, 2001). This warrants asking the question of whether it is expressive language abilities which may be impeding expressive prosodic abilities. The current study is unable to address this question because no measures of expressive language ability were taken. This is a question that future research needs to address. With regard to the third research question, the results from the correlations showed that receptive language skills do not seem to be related to prosodic abilities in children with DS. There was only one significant correlation for the DS group and it related to a prosody form task. Previous studies of typical populations have shown that aspects of intonation performance and language abilities in typically developing children are highly correlated (Local, 1980; Wells et al., 2004). Stojanovik et al. (2007) also showed that performance on the TROG was highly correlated with performance on a number of comprehension function prosody tasks in typically developing children. The lack of significant correlations between language and prosodic skills in the group of individuals with DS in the present paper suggests that linguistic and prosodic abilities may not support each other in the same way as they do in typically developing children. However, this should be taken with caution, given the small number of participants with DS in the current study although it should be noted that relative independence of linguistic and prosodic abilities has been reported for children with speech and language deficits of different etiologies (Wells et al., 2004) and for children with Williams syndrome (Stojanovik et al., 2007), and both of these studies had larger groups of participants. These reports, coupled with the data from the present study suggest that prosody may be a cognitive skill which is discreet from other linguistic abilities and may be an independent cognitive domain which is not closely linked to other

2

On the formal aspects of intonation, the differences between comprehension and production were marginal for all groups.

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linguistic abilities. This would suggest that individuals with DS may not be relying on prosody as much when acquiring language as typically developing infants do, but we need to investigate the sensitivity to intonation cues in preverbal infants with DS and their language development in order to address this question. Acknowledgements Part of this research was supported by award RES-000-22-1302 from the Economic and Social Sciences Research Council !supportNestedAnchors]>]> (ESRC, UK) to Vesna Stojanovik and Jane Setter. I would like to thank Laura Wyllie for collecting the data from the participants with Down syndrome and to Lizet van Ewijk for collecting the data from the typically developing controls. Also, many thanks to DownsEd International who helped with the recruitment of participants with Down syndrome and to Dr Jane Setter for her help with the inter-rater reliability for the control participants. Appendix 1.Description of the PEPS-C tasks (also described in Stojanovik et al., 2007) Function tasks Turn-end (interaction) Assesses the testee’s ability to understand and produce the function of intonation in interaction, by looking at conversational turns consisting of a single word. The words are items of food and by the nuclear tone (a fall or a rise) the testee is asked to decide whether an item was read from a book (a fall), as opposed to offered by someone (a rise) by selecting the correct picture on the screen upon hearing the word (there are only two choices on the screen). For the production task, the testee sees only one picture on the screen, i.e. either somebody offering something on a plate or somebody reading the item from a book and the testee has to produce the words by using the appropriate nuclear tone. An error was counted when the child produced a different nuclear tone to the target one (for example, the child produced a fall and a rise was required). Level tones were also counted as errors. Non-responses, or responses which did not contain the target word, were not counted as errors. For all production tasks, the tester sits out of sight of the screen and judges which picture the testee was seeing by selecting an option on a keypad connected to the computer. Affect Assesses the testee’s ability to distinguish between liking versus disliking expressed in intonation on single words. Likes are conveyed by a rise–fall pitch contour whereas dislikes are conveyed by a fall–rise pitch contour. The stimuli involve pictures of different foods and drinks. In the Comprehension task the testee had to decide whether the person recorded on the computer liked or disliked a particular food item, which they did by selecting a smiley face or a sad face. In the Production task, the testee was shown different food items and they had to express their own liking or disliking for each food item using appropriate intonation. As in the Turn-end tasks, the errors in the production were counted when the testee produced a different nuclear tone to the one which was required or they produced a level tone. Non-responses or responses which did not contain the target word were not counted as errors. Chunking Assesses the testee’s ability to perceive and produce grammatically ambiguous sentences and phrases which are disambiguated using prosody. The stimuli include pictures of food items and different-coloured socks. There are eight items involving compound nouns and eight involving two nouns. Chunking refers to prosodic delimitation of the utterance into units (or intonation phrases) for grammatical, semantic or pragmatic purposes, e.g., /FISH-FINGERS/AND FRUIT/ vs. /FISH/FINGERS/AND FRUIT/. In the first utterance the absence of a separate intonation phrase for FISH FINGERS constitutes ‘‘fishfingers’’ as a compound noun. In the second utterance, there are three intonation phrases, each with its own accent, constituting the utterance as a list of three food items. In the Comprehension task, the testee was shown two pictures, one which contained two items and the other one which contained

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three items and the testee was asked to select the correct picture having heard the voice on the computer. In the Production task, the testee was shown only one picture containing either two or three items and they had to produce it using either two or three intonation phrases respectively. Focus Assesses the testee’s ability to identify and produce contrastive stress (tonicity). In the Comprehension task the testees heard a sentence in which one of two colours was stressed. They were asked to say which one it was. For example: ‘I wanted BLUE and white socks’, BLUE was stressed and the testee had to point to the blue picture. In the Production task the testees were presented with a football match between different-coloured cows and sheep. Each time one of the animals had the ball the testee would hear a voice giving an erroneous description of the situation. E.g. for a picture of a blue cow, the testee would hear ‘‘the red cow has the ball’’. The testee was asked to correct the voice on the computer – i.e. by saying: No, the BLUE cow has it! For each situation either the colour or the animal had to be changed.

Form tasks These tasks assess the testee’s ability to perceive and produce various intonation and prosodic differences. Short-item and long-item discrimination tasks These involve a same/different procedure. The testee is presented with stimuli in a form where the lexical and grammatical information is not audible. The stimuli consist of the laryngograph signal only, derived from spoken pairs, such as the ones in the Short-item and Long-item imitation tasks. Pitch, loudness and length variations are preserved. The result is a ‘buzz’ – not dissimilar to listening to a speaker in an adjacent room, where the intonation is audible, but the content of the utterance is not. The testee needs to decide whether the two stimuli are the same or different by clicking on either a picture which contained two red balls, or by clicking on a picture which contained a red ball and a green square. Short-item and long-item imitation tasks These tasks assess the testee’s ability to imitate different intonation or prosodic forms. For the short-item task the testee heard a single word with a particular intonation pattern and was asked to repeat that word in exactly the same way as they heard it. For the long-item task the testee heard an utterance with a particular prosodic form (e.g. GREEN and black socks) and was asked to repeat the phrase in exactly the same way as they heard it.

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