Simple and Complex Manual Sequence Learning in School-Aged Children with Typical Development and with Developmental Language Disorder

Abstract

The goal of this dissertation was to examine how children, both with typical development and with developmental language disorder (DLD) learn two types of sequences, important for language, in the manual domain. We sought to better understand the developmental trajectory of statistical learning in the manual domain and investigate the extent to which cognitive mechanisms underlie language learning in general and DLD in particular. Specifically, we distinguished between two types of learning on a domain-general, modified Serial Reaction Time (SRT) task: local transitional probabilities versus abstract exclusive disjunctive (XOR) rules. Typically developing (TD) infants can learn phonotactic XOR rules that adults cannot (e.g., Dell et al., 2021; Gerken et al., 2019), but the developmental trajectory of this ability throughout childhood is not well understood. Research on rule-learning has predominantly focused on phonotactic patterns; it remains unclear whether the learning process is specific to language or applies more broadly across domains. Here, we assessed the extent to which TD school-aged children learned both a simple pattern involving local transitional probabilities (Word condition), and a complex pattern involving abstract XOR rules (Grammar condition), on a domain-general modified SRT task. This dissertation also served to inform theoretical accounts of DLD. Children with DLD are classically identified by their grammatical deficits (e.g., Leonard, 2014), but often display co- occurring weaknesses in other areas, including speech-motor organization (e.g., Benham et al., 2018), and fine/gross motor skill (e.g., Hill, 2001). We anchored this dissertation in the hypothesis that a domain-general sequential pattern learning deficit (of specific sequence types) unifies language, speech, and motor difficulties attested in DLD. Critically, the sequences in the patterned blocks of our SRT task are derived from components of language that are relative linguistic strengths (i.e., word boundary parsing) or linguistic weaknesses (i.e., morphosyntactic learning) among children with DLD. The rules governing the sequences are novel for SRT tasks and are important for specifying the precise nature of a potential domain-general sequential learning impairment in DLD. The second goal of this dissertation was to assess the extent to which children with DLD learned local transitional probabilities (Word condition), and abstract XOR rules (Grammar condition), on the domain-general modified SRT task. Children aged 5-8 years with TD (n = 26) and DLD (n = 9) participated. TD participants demonstrated evidence of learning in both the Word and Grammar conditions, though learning appeared to be more protracted in the Grammar condition. There was not strong evidence that participants generalized the XOR rule. Overall, these results suggest that TD children are sensitive to local transitional probabilities and to abstract XOR rules in a domain-general task into the early school years. Preliminary results revealed that school-aged children with DLD are sensitive to local transitional probabilities, but not to a complex XOR rule, on a domain-general SRT task. This supports an account of DLD in which specific sequence learning, conceptually aligned with grammatical structure, is implicated across domains. Specifying a nonlinguistic mechanism of DLD may lead to more targeted interventions and earlier identification across dialects/languages using domain-general measures