Objectives: To investigate auditory (semantic) language processing in children with ASD and typically developing children in order to determine electrophysiological correlates of brain activity during automatic language processing. The aim was also to establish any behavioural and clinical indicators as well sensory abnormalities in ASD children which correlate with specific parameters of brain activation.
Methods: 11 high functioning boys (mean age 13years) with a diagnosis of autism spectrum disorders and 11 typically developing boys (mean age 13 years 7 months) participated in an auditory oddball task using words, nonwords and phonemes. Both groups were matched for age, gender, verbal and nonverbal IQ and handedness. All children with ASD completed the Adolescent Sensory Profile. Children engaged in a mismatch negativity task, a widely used ERP paradigm to test automatic auditory and semantic processing (see Endrass et al, 2004, Shtyrov and Pulvermüller, 2007). Participants were seated in front of a computer screen watching a silent film of their choice and were instructed to ignore the stimuli. Words and pseudowords were presented auditorily while mean ERP amplitudes and latencies for each stimulus type was calculated. EEG activity was measured from 32 electrodes.
Results: A significant interaction on amplitude response was present between the two groups of children and the words and pseudoword conditions. Further analysis revealed significantly reduced MMN responses to words in ASD children compared to typically developing children but no differences were found for pseudowords. Furthermore, the autism group showed similar amplitude responses across words and pseudowords. In addition, evidence of reduced attentional orienting to sound changes involving frequency and loudness was present. Behavioural data revealed auditory over-responsiveness to be the most common and pervasive form of sensory behaviour within the ASD group and key differences were observed in low registration, sensory sensitivity and sensory avoidance. The mean ERP amplitude for both, words and pseudowords was highly correlated with sensory sensitivity scores.
Conclusions: It is likely that the children deliberately avoid or prevent exposure to sensory stimuli (sensory avoidant) and the preventative strategies which they use may be related to impairments in language processing. We discuss how the expression of sensory behaviours (actively withdraw from environment) may modulate the degree to which sounds are detected and missed in the environment.