While most children learn their native language seemingly effortlessly, some 7% of children are severely delayed in their linguistic development, a condition known as Developmental Language Disorder (DLD). The causes of DLD are poorly understood.
This is partly because the symptoms that children show differ markedly across different languages. Children with DLD learning English have great difficulty learning to use verb endings correctly. These children will continue to produce utterances like ‘he go home’ instead of ‘he goes home’ long after typically developing (TD) children have grasped that 3rd person singular verbs need an -s ending. Somewhat surprisingly, both DLD and TD children learning Spanish are far quicker to learn verb endings, despite the fact that Spanish has six different present tense forms for each verb compared to only two (e.g., go vs. goes) in English. Why is it easier for children to learn verb endings in Spanish? And why don’t Spanish verb endings seem to pose major problems even for children with DLD?
Why is it easier to learn verb endings in Spanish?
Part of the answer appears to be that, despite having more different forms, Spanish is highly regular, and uses distinct forms for different person/number combinations (e.g., I, you, (s)he, we, they), while English uses the same bare form (go) for all but the 3rd person singular (he/she) form (goes). This is complicated further by the fact that English also uses the bare form in 3rd person singular questions (where does he go?). Finally, English makes extensive use of the progressive construction (he’s going) which uses the same form (going) in all person/number combinations. This construction is less common in Spanish. So, while the Spanish system may seem more complex, the English system is more confusing, and children need to work out when the final -s is and isn’t required.
How did we test this explanation?
Researchers at the University of Liverpool recently tested this explanation by using a computer model that learns to associate the different endings of verbs with the contexts in which they are used. They searched transcripts of English and Spanish speech directed at language-learning children for verbs and counted how often different forms of verbs (e.g., go, goes, going), occurred in different contexts (e.g., I, you, he, he’s). Next, they trained the computer model to predict the verb ending (none, -s, -ing for English), based on the identity of the verb and the context. English and Spanish models were trained on an equal number of trials, that represented the distribution of the different forms and contexts for the 30 most common verbs in the language, and the model’s ability to associate contexts and suffixes was manipulated. The researchers were able to show that the model was far quicker to learn the common Spanish verb endings, than the English third person singular ending. They also showed that the difference between Spanish and English became more pronounced when the model’s ability to associate contexts and endings was impaired. Under these conditions the model displayed a tendency to ‘default’ to the most common form for a verb or context. In English this tends to be the bare form (go) or progressive (going). In Spanish, which isn’t dominated by any one form in the way that English is, defaulting played a minor role. The researchers also trained a model on English input with questions and progressive constructions removed, and were able to show that, with the confusing and distracting constructions removed, the English system became more like Spanish, and the model was far quicker to learn the 3rd person singular ending.
What does this tell us about DLD?
This research suggests that Developmental Language Disorder is at least partly characterised by a deficit in associative learning. This deficit manifests itself differently in different languages because the structure and statistics of the languages differ. On the face of it, Spanish may seem more complex, as it has more forms. However, since Spanish is highly regular, it is easy to distinguish the contexts in which the different forms are used. English on the other hand, uses fewer forms, and uses the third singular form inconsistently. So, it becomes a challenge for children to work out when the final -s is required, and children tend to produce more frequent bare and progressive forms instead. The research does not provide a ‘cure’ for DLD. However, by showing that a common deficit can manifest itself differently in different languages, it has the potential to inform therapies cross-linguistically.
Freudenthal, D., Ramscar, M., Leonard, L. B. & Pine, J. M. (2021). Simulating the acquisition of verb inflection in typically developing children and children with Developmental Language Disorder in English and Spanish. Cognitive Science, 45(3), e12945.