Specificity of Atypical Neural Development for Language in Infants at Risk for ASD
Delayed language development is a characteristic feature of Autism Spectrum Disorder (ASD). An important skill that develops before children produce speech is the ability to discriminate speech sounds. Research has identified abnormal perceptual narrowing in infants at high risk for ASD (Seery 2010). However, given that multiple developmental conditions are associated with language delay, it is unknown whether these findings are specific to ASD to reflective of non-specific developmental disturbance. Sagittal craniosynostosis (SC) and deformational plagiocephaly (DP) are conditions associated with language delay and subsequent learning disability (Magge 2002). Given that SC, DP, and ASD may all affect infants early in development and exert potential impact on language development, patients with SC and DP are an appropriate clinical comparison group to investigate the specificity of atypical perceptual narrowing in ASD.
The present study aims to contrast the neurophysiological response to language stimuli in infants at high risk for ASD (HR-ASD) with infants with non-ASD conditions that affect auditory processing. Findings will be compared to infants at normal risk for ASD (NR).
Four groups of infants from English-speaking families participated in the current study: 12 infants at high risk for ASD (by virtue of having an older sibling diagnosed with the disorder); 12 infants with SC; 20 infants with DP; and 24 NR infants. Participants were divided into two age groups: a) between 3-9 months and b) between 10-17 months. EEGs were recorded with a 128 channel HydroCel GSN net during auditory presentations of non-native dental /da/ and retroflex /Da/ phonemes. EEG data was analyzed to extract ERPs evoked by phonemes (P150, a positive deflection over left and right anterior scalp between 100 and 300 ms, and N450, a negative deflection over the left and right temporal scalp between 400 and 550 ms).
Preliminary analyses contrasting the peak amplitudes of ERPs in response to the dental and retroflex phonemes revealed that NR control infants between 3 and 8 months differentiated the two phonemes (mean difference= 3.56 microvolts). Analyses in progress contrast peak amplitudes across clinical groups and across developmental cohorts. We predict that at earlier ages, infants with HR-ASD, SC, and DP will demonstrate discrimination of the non-native phonemes similar to controls. However, we predict that the HR ASD, SC, and DP groups will demonstrate persistent discrimination of the non-native phoneme at later ages relative to normal-risk subjects, indicating deviant language development.
Results will provide insight into the underlying processes behind abnormal neurophysiological responses to language in ASD. By contrasting the specific patterns of atypical neural development in ASD with other clinical groups, this study will provide critical information regarding the specificity of atypical development in ASD.