Introduction

Williams syndrome (WS) is a rare neurodevelopmental disorder present in about 1 in 7,500 to 20,000 live births and caused by a micro-deletion on one copy of chromosome 7, which results in atypical physical, cognitive and behavioural phenotypes (Kozel et al., Reference Kozel, Barak, Kim, Mervis, Osborne, Porter and Pober2021; Royston et al., Reference Royston, Waite and Howlin2019; Tassabehji et al., Reference Tassabehji, Metcalfe, Karmiloff-Smith, Carette, Grant, Dennis, Reardon, Splitt, Read and Donnai1999). Individuals with WS have been described as presenting with relatively good vocabulary and phonological skills and relatively spared grammar in the face of weaker pragmatic skills and moderate-severe deficits in nonverbal tasks including problem solving, spatial and number cognition and planning (Mervis & John, Reference Mervis and John2010). Reports have also highlighted relatively good performance on complex language structures such as passives, negations, and conditionals (Bellugi et al., Reference Bellugi, Marks, Bihrle and Sabo1988, Reference Bellugi, Wang and Jernigan1994), inflections and derivations (Clahsen & Almazan, Reference Clahsen and Almazan1998) as well as increased use of narrative enrichment devices (Bellugi et al., Reference Bellugi, Wang and Jernigan1994). Such observations made WS a popular example supporting the idea of an independent “language module” containing abstract grammatical representations (Pinker, Reference Pinker1999; Zukowski, Reference Zukowski2005).

This assumption of a relative strength in language has been challenged by studies arguing that language in individuals with WS is either delayed or less developed than expected for their mental age. For example, individuals with WS produced more errors in the areas of lexical selection, word order, gender agreement and verb inflections, and showed poorer grammatical comprehension compared to neurotypical controls (Karmiloff-Smith et al., Reference Karmiloff-Smith, Grant, Berthoud, Davies, Howlin and Udwin1997; Volterra et al., Reference Volterra, Capirci, Pezzini, Sabbadini and Vicari1996). Individuals with WS also performed similarly or less well than populations with comparable intellectual skills such as Down syndrome on processing wh-questions and passives (Joffe & Varlokosta, Reference Joffe and Varlokosta2007). Furthermore, children with WS showed no verbal advantage over children with developmental language disorder on standardized tests or a narrative task (Stojanovik et al., Reference Stojanovik, Perkins and Howard2004). Thomas et al. (Reference Thomas, Grant, Barham, Gsödl, Laing, Lakusta, Tyler, Grice, Paterson and Karmiloff-Smith2001) reported that participants with WS had difficulties generalizing past tense rules to novel verbs, often omitting obligatory inflections. Expressive language has been described as stylistically different, featuring atypical vocabulary, stereotyped phrases, idioms, overfamiliar language and excessive use of social evaluative devices including prosodic cues and dramatic narrative elements (Reilly et al., Reference Reilly, Losh, Bellugi and Wulfeck2004; Thomas et al., Reference Thomas, Dockrell, Messer, Parmigiani, Ansari and Karmiloff-Smith2006; Udwin & Yule, Reference Udwin and Yule1990), although these findings have not always been replicated (Crawford et al., Reference Crawford, Edelson, Skwerer and Tager-Flusberg2008; Stojanovik & van Ewijk, Reference Stojanovik and van Ewijk2008).

The neuroconstructivist explanation has been that rather than accessing a preserved language module, individuals with WS acquire language in a qualitatively different manner (Karmiloff-Smith et al., Reference Karmiloff-Smith, D’Souza, Dekker, Van Herwegen, Xu, Rodic and Ansari2012; Levy & Eilam, Reference Levy and Eilam2013; Thomas et al., Reference Thomas, Grant, Barham, Gsödl, Laing, Lakusta, Tyler, Grice, Paterson and Karmiloff-Smith2001). Pointing and categorization emerge late relative to lexical acquisition (Laing et al., Reference Laing, Butterworth, Ansari, Gsödl, Longhi, Panagiotaki, Paterson and Karmiloff-Smith2002), and the developmental trajectory has been characterized by a stronger correlation between grammatical capacity and verbal working memory (Robinson et al., Reference Robinson, Mervis and Robinson2003). One proposal is that language processing in WS relies less on grammatical and lexical-semantic information and more on shallow acoustic and phonological features, with a bias towards imitation (Thomas & Karmiloff-Smith, Reference Thomas and Karmiloff-Smith2003). An individual with WS may produce phrases or utterances because they heard them before and represent them as one unit, and not because they use abstract grammatical information to combine individual words and morphemes. This more shallow production may give the appearance of unaffected processing.

Such explanations call for the distinction between analytic and holistic (or gestalt) processing, which is rooted within usage-based linguistics (e.g., Jackendoff, Reference Jackendoff2003; Langacker, Reference Langacker1987; Tremblay & Baayen, Reference Tremblay and Baayen2010). Analytic processing uses abstract representations of phrasal structures to combine individual words and morphemes and is able to generate novel expressions. Holistic processing, on the other hand, involves learning and retrieving word combinations, such as single phrases, but also entire sentences, as a single unit (a formula). Imitation can be driven by holistic representations; however, holistic forms are also an essential part of everyday language use (van Lancker Sidtis & Rallon, Reference van Lancker Sidtis and Rallon2004). Theories such as construction grammar (Goldberg, Reference Goldberg2006, Reference Goldberg2019) suggest that everyone uses both analytic and holistic processing, with the contribution of each changing depending on situational requirements. While proficient speakers have the capacity to analyze these utterances, in principle holistic phrases can be used without grammatical and lexical-semantic interpretation of their individual constituents.

It has been proposed that in typical development, children first primarily employ holistic processing, resulting in conservative and repetitive production of language formulas, and only later acquire more abstract grammatical representations that, along with lexical growth, enable more creative and flexible language (Bannard & Matthews, Reference Bannard and Matthews2008; Lieven et al., Reference Lieven, Salomo and Tomasello2009). Faster and more accurate processing of formulaic language in adults suggests that holistic knowledge remains relevant even after maturation (Conklin & Schmitt, Reference Conklin and Schmitt2012; Tremblay & Baayen, Reference Tremblay and Baayen2010). Formulaic language is also more likely preserved in people with neurological conditions such as aphasia or dementia (van Lancker Sidtis, Reference van Lancker Sidtis2012; Zimmerer et al., Reference Zimmerer, Newman, Thomson, Coleman and Varley2018, Reference Zimmerer, Hardy, Eastman, Dutta, Varnet, Bond, Russell, Rohrer, Warren and Varley2020). Because formulas can be long and morphologically rich, they give the impression of islands of intact grammatical knowledge, when instead they are likely either well-trained combinations or lexicalized multiword sequences.

Since one predictor of holistic representations is frequency of (co-)occurrence of words in everyday language use, acquisition of formulaic phrases is supported by sensitivity to statistical patterns in language. In WS, this sensitivity has been demonstrated in artificial language learning studies. Using the word segmentation learning paradigm, Cashon et al. (Reference Cashon, Ha, Graf Estes, Saffran and Mervis2016) demonstrated that 20-month-old infants with WS could distinguish words from part-words after brief familiarization with statistically structured syllable sequences. Stojanovik et al. (Reference Stojanovik, Zimmerer, Setter, Hudson, Poyraz-Bilgin and Saddy2018) found that participants with WS prefer statistical representations to more abstract grammatical rules. They compared processing biases in artificial language learning performances between participants with WS, mental-age matched typically developing (TD) children, and chronological-age (CA) matched TD individuals. In a brief familiarization phase, participants listened to spoken syllable sequences generated by a simple Markov-grammar. It was explained that sequences were magic spells, and they were presented along with a cartoon magician. In the test phase, participants distinguished between correct and incorrect “spells” based on what they learned from the familiarization set. Participants with WS and younger, mental-age matched TD children preferred sequences that resembled exemplars from familiarization. CA-matched TD participants, on the other hand, accepted sequences that were grammatical, regardless of familiarity, demonstrating their ability to acquire more abstract grammatical knowledge. These results suggest that TD individuals switch from familiarity- to rule-based processing in their development while, in individuals with WS, the bias towards familiarity may remain for much longer.

Based on current evidence, one could hypothesize that natural language processing in WS would also be atypically biased towards co-occurrence of specific words and acquisition of holistically processed, formulaic language. Do individuals with WS produce more familiar language? In this current study we examined statistical properties of words and word combinations in narrative samples of individuals with WS, who we compared with CA and language-age matched (LA) TD controls to identify both delays and atypical trajectories.

We determined the usage-frequency of each word in a narrative sample, using the spoken section of the British National Corpus (BNC XML Edition, 2007) as reference. Higher frequency indicates that a word is more common in typical language use, which has been associated with ease of production. We analyzed word combinations by determining their collocation strength, again using the BNC as reference. Collocation strength shows how often words appear together, relative to how often each occurs in general. Collocation strength is therefore not merely a function of frequency. For example, I go is a more frequent bigram than I tell according to the BNC; however, the collocation strength of the latter is seven times as high, because when the words I and tell occur, they more likely appear together relative to appearing in other contexts. We extracted these variables using the Frequency in Language Analysis Tool (FLAT), a script which had previously been employed to study statistical properties of language production in adults with stroke aphasia (Zimmerer et al., Reference Zimmerer, Newman, Thomson, Coleman and Varley2018) and neurodegeneration (Zimmerer et al., Reference Zimmerer, Hardy, Eastman, Dutta, Varnet, Bond, Russell, Rohrer, Warren and Varley2020).

This study is a secondary analysis of language transcripts collected by Stojanovik et al. (Reference Stojanovik, Setter and van Ewijk2007), originally for their investigation of intonation. They found that the ability to produce and understand intonation of participants with WS was poorer than that of CA-matched controls, but mostly in line with language-age (LA)-matched controls. A subsequent study by Stojanovik and van Ewijk (Reference Stojanovik and van Ewijk2008) investigated lexical production. The authors report that individuals with WS did not differ from controls with regards to lexical diversity and the number of low frequency words produced.

We investigated additional features in order to present a broader profile and context and to address our questions regarding holistic vs. analytic processing. Our analysis includes two dimensions of language production: (1) complexity, which includes mean length of utterance (MLU), proportion of complex sentences, verb phrase complexity, and morphosyntactic errors, and (2) familiarity, which includes a more comprehensive measure of lexical frequency than the one used by Stojanovik and van Ewijk (Reference Stojanovik and van Ewijk2008), and the collocation strength of word combinations. While we predicted that CA-matched controls would produce the most complex and least familiar language, while individuals with WS would produce the least complex and most familiar language, our statistical analyses tested broader hypotheses, namely that groups would differ from another.