Fast-Mapping In Boys with Autism and Fragile X Syndrome

Background:

“Fast-mapping” describes the process by which children make an associative pairing between label and referent during initial word learning. Despite its relevance to lexical acquisition, no previous study has assessed fast-mapping in fragile X syndrome (FXS), an inherited cause of intellectual disability and comorbid autism.  Research comparing word learning in children with FXS and autism has the potential to clarify factors that contribute to overlapping ability profiles. The current study examined fast-mapping in boys with autism, FXS, and typical development.

Objectives:  

• To compare fast-mapping across groups after controlling for nonverbal cognitive ability.
• To examine concurrent associations between fast-mapping and nonverbal cognition, autism severity, and vocabulary.
• To examine the potential contribution of task demands to fast-mapping performance.

Methods:  

Participants were boys with autism (n = 16; ages 4-10 years), FXS (n = 32; ages 4-10 years) and typical development (n = 36; ages 2-6 years).  Leiter-R Brief IQ growth scores provided a measure of nonverbal cognition; participants with autism and FXS had IQs between 36 and 80. Autism symptom severity was calculated from the ADOS. The Peabody Picture Vocabulary Test-4 and Expressive Vocabulary Test-2 provided the measures of vocabulary. The fast-mapping task consisted of four trials, each with an exposure and test phase. During each exposure phase, two novel objects were sequentially presented. The target object was accompanied by 5 presentations of a nonsense label (e.g., dawnoo) embedded in connected speech. The foil object was accompanied by an equivalent amount of talking without labeling. Side and order of presentation were randomized. During each testing phase, the child was asked to find the labeled object when both objects were presented simultaneously. The dependent variable was the number of correct choices out of four.

Results:  

• After controlling for nonverbal cognition, TD boys did better at fast-mapping than did boys with autism or FXS (both ps < .001), who did not differ from one another (p < .939).
• For boys with autism, there were significant associations between fast-mapping scores and (1) nonverbal cognition (r = .50, p < .024), (2) receptive vocabulary (r = .57, p < .01), and (3) expressive vocabulary (r = .71, p <.001). For boys with FXS, only the association between fast-mapping and receptive vocabulary was significant (r = .42, p < .008). Autism symptom severity was not related to fast-mapping scores. For TD boys, no correlations were significant.
• Order of target presentation during exposure (first or second) impacted fast-mapping scores for TD boys, whose performance was better when the target object was presented second (i.e., immediately before the test phase; p < .03).

Conclusions:  

After controlling for nonverbal cognition, fast-mapping performance was similar for boys with autism or FXS, but impaired relative to cognitively matched TD boys. Participants with autism or FXS did not show increased difficulty when presentation order required them to hold the novel label in mind longer, leading to questions about what other factors might impact word learning performance (e.g., attention, perseveration). Implications for interventions targeting word learning will be discussed. Data collection is ongoing.