Electrophysiological Correlates of Speech Perception in 9 Month Olds At Risk for ASD

Background: Between 6 and 12 months, typically-developing infants undergo a process of perceptual narrowing where they lose the ability to perceive the phonemic contrasts that are not used in their native language (e.g., Werker & Tees, 1984; Rivera-Gaxiola, Silva-Pereyra, & Kuhl, 2005).  Our recent ERP work suggests that infants who are at a high risk for developing ASD (HRA; at risk due to having an older sibling with a diagnosis) do not necessarily appear delayed in undergoing this perceptual narrowing.  However, it is possible that infants who ultimately develop ASD show a different trajectory, especially since the process may depend on social engagement with a speaker.

Objectives: Here, we collected ERP to speech sounds in order to study perceptual narrowing in 9-month-old infants at risk for ASD.  Importantly, we expanded an original sample substantially, allowing us to again examine our original finding of no delay in the HRA group in addition to looking more closely at the 20% of HRA infants who we expect to ultimately develop ASD.

Methods: We collected ERP while using a double-oddball paradigm to present infants with a stream of three consonant-vowel speech sounds: a standard (presented 80% of the time), a non-native deviant (10%), and a native deviant (10%). In this sample, we included data from 127 9-month-old infants (60 HRA and 67 LRC); to date, 7 of the HRA infants have received a diagnosis of ASD (4 confirmed through clinical review at 36 months; 3 suspected due to symptoms at 18 or 24 months). 

Results: We used a repeated-measures 3x2x2 ANOVA (condition x hemisphere x group) to examine the maximum amplitude of a linguistic ERP component, the P150, over frontal electrodes in HRA versus LRC infants.  This revealed a main effect of condition (F(2,250)=9.603, p<.001), as expected from our previous work.  Specifically, the P150 amplitude was larger to both the native (average maximum amplitude=7.48μV) and non-native (6.49μV) deviants than to the standard (5.30μV; p<.05 for both paired comparisons).  Critically, there was no main effect of or interaction with group (both p>.6).  However, we found a somewhat different pattern of response in the group of infants with a positive ASD diagnosis.  In these infants, we found no difference in the P150 amplitudes of the three stimuli (standard: 7.44μV, native: 7.79μV, non-native: 6.41μV).

Conclusions: Our data suggest that 9 month olds at risk for ASD, as a group (most of whom will not be diagnosed with ASD), do not differ from typically-developing infants in their phonemic perceptual narrowing (at least as measured by P150 amplitude).  However, looking at this component specifically in the infants who do ultimately develop ASD (although the group size is relatively small), we found preliminary evidence for a lack of sensitivity to the type of speech sound that was presented.  Future work will investigate this finding more closely and will examine possible factors, such as attention, that might contribute to it.