Abstract:

Vocabulary delay is prevalent in children with autism spectrum disorder (ASD), yet there is no converging evidence regarding its underlying mechanisms. Although there is evidence that they can employ word learning constraints such as mutual exclusivity, cross-situational statistical learning to learn words, children with ASD still demonstrate vocabulary delay. This discrepancy can be ascribed to atypical general learning mechanisms supporting word acquisition in children with ASD. Attention and memory are two general cognitive mechanisms involved in word learning. Numerous studies have shown that atypical attention and memory are observed in children with ASD, which may have a downstream cascading effect on their word learning. Social attention provides critical information for word learning. Typically developing children can follow others’ gaze and show sustained attention to target objects in joint attention episodes to establish word-referent associations, whereas children with ASD show diminished sustained attention to target objects although they exhibit intact gaze following behavior. In addition, children with ASD are easily distracted by salient but irrelevant stimuli in the environment and have difficulty with attentional disengagement. As a result, word-referent relationships established by children with ASD are weak. After building word-referent associations, the consolidation of these associations is also critical to word learning. According to Complementary Learning Systems (CLS) account, episodic memory and semantic memory are involved in the consolidation of new words. At the initial stage of learning, also known as rapid initial familiarization stage, new words are encoded as discrete episodes of experiences in the episodic memory network. At the slow lexical consolidation stage, individuals experience a more systematic, lexicalized coding of the memory representation that occurs in the neocortex during sleep. In typically developing children, sleep contributes to the consolidation of new words, while children with ASD receive less benefit form sleep-associated consolidation specific to new words. Abnormalities in sleep might have negative consequences on children with ASD’s word consolidation and retention. Drawing upon these observations, we reasoned that word-referent links established by children with ASD are weak due to altered attention and these weak lexical traces may not be able to access consolidation through sleep, resulting in higher forgetting rate and vocabulary delays in children with ASD. Accumulating evidence suggests that vocabulary delay in children with ASD might be attributed to attenuated attention and memory, yet so far, the majority of studies have separately investigated the role of attention and memory in word learning and research that examines whether atypical attention contributes to poor consolidation of new words remains limited, which calls for more empirical evidence. In addition, further work is required to investigate the developmental trajectory and mechanisms underlie the link between joint attention and word learning, the influence of existing lexical knowledge of children with ASD on word retention. Moreover, previous studies on children with ASD’s word learning have extensively focused on whether children could use lexical constraints to learn words while the role of parent behaviors in children with ASD’s word learning is understudied. Therefore, in children with ASD, child-parent coordination and the contribution of parent behaviors in the word learning process require further investigation. Further, since language development in children with ASD is heterogeneous, future studies should investigate the influence of attention and memory on word learning in children with ASD with a wide range of cognitive and language abilities, which can inform the practitioners to develop targeted language interventions. Finally, it is also worth investigating whether attention and memory play a role specific to word learning but not in other domains of language acquisition such as grammar acquisition, which will enhance our understanding of the mechanisms of language acquisition.

Key words: vocabulary development, word learning, attention, memory, autism spectrum disorder