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Understanding the Link between Language Abilities, Broader Autism Phenotype, and Atypical ERPs to Words in Toddlers with and without ASD
Atypical neural responses to speech have been found in toddlers with ASD and in their unaffected siblings (Kuhl et al., 2013; Seery et al., 2013). However, given that language difficulties are often seen in these populations, it is difficult to interpret whether these neural differences are a result of the ASD diagnosis or impairments in their language abilities.
Objectives:
Our study investigated event-related potentials (ERPs) to words in 36-month-olds with and without ASD, including those at familial risk with and without the broader autism phenotype (BAP). We also controlled for language abilities in our analyses.
Methods:
Participants
74 monolingual, English-speaking 36-month-olds were divided into four groups: low-risk control (LRC; N=31), high-risk for ASD (HRA; older sibling with ASD) without ASD or BAP (HRA-Typ, N=16), HRA without ASD with BAP (HRA-Atyp, N=13) and HRA with ASD (ASD; N=14).
Procedure
EEG was recorded while toddlers passively listened to a stream of words. Forty nouns were presented up to three times across two categories: 1) words acquired ‘early’ (understood by 18-month-olds according to the MCDI normative data) and 2) words acquired ‘late’ (not included on the MCDI; Dale & Fenson, 1996).
Analysis
Analysis focused on the mean amplitude of the N200 (200-350ms post-stimulus onset) and N350 (350-500ms post-stimulus onset) as their distribution varies depending on word familiarity (Mills et al., 2005). Two regions of interest from each hemisphere were constructed: frontal and temporo-parietal. We performed ANOVAs with condition (early, late), time bin (200-350ms, 350-500ms), and hemisphere (left, right) as within-subjects factors and group (LRC-Typ, HRA-Typ, HRA-Atyp, ASD) as a between-subjects factor. Average amplitude of the frontal and temporo-parietal sites were the dependent variables. We controlled for language abilities using the verbal developmental quotient from the Mullen Scales of Early Learning (Table 1).
Results:
Within the frontal sites, there were no significant main or interaction effects.
Within the temporo-parietal sites, we found a significant hemisphere by group interaction (F(3,69)=3.52, p=0.020). This interaction was driven by group differences in the left hemisphere (p=0.041), but closer inspection within the left hemisphere revealed no differences between the groups (all p>0.070). We found a significant condition by time by group interaction (F(3, 69)=2.96, p=0.038). This was driven by the HRA-Atyp children showing a more negative response in the N200 for the late words compared to the LRC-Typ (p=0.046) and ASD children (p=0.004). There were no other significant main or interaction effects.
Conclusions:
When controlling for language abilities, the HRA-Atyp group showed a different timed response to late words compared to the ASD and LRC groups in the temporo-parietal sites. This difference may reflect a weaker lexical representation of words in the HRA-Atyp toddlers compared to the LRC toddlers. The difference between the HRA-Atyp and ASD groups is surprising, but perhaps this is due to the variability often seen in the language abilities of children with ASD, including in our own sample. Our results suggest that both language abilities and ASD symptoms are important to consider when interpreting neural differences in lexical processing