Autism spectrum disorders (ASDs) are characterized by immense heterogeneity – from individuals with high-functioning autism (HFA) who demonstrate only limited deficits in social communication, to those who are low-functioning (LFA) and fail to develop any shared symbolic system of communication. It has been posited that typical infants utilize “prosodic bootstrapping” to acquire vocabulary and develop oral language: Child-directed speech presents infants with a unique affective speech register that cues them to distinguish individual speech sounds in their native language. Yet research has found that very young children with ASD are less responsive to their mother’s voice, which may hinder successful language acquisition. Perhaps the ability to perceive affective prosody is at the core of language and communication difficulties in the minimally verbal LFA subgroup, approximately 30% of the ASD population. While recent scientific inquiry has made gains regarding ASDs, little research examining the minimally verbal LFA subgroup has been undertaken to date. The present study sought to fill this gap, through an investigation of the ability of children on the autism spectrum, including minimally verbal LFA, to perceive angry, neutral, and happy prosody in low-pass filtered speech when provided with a structured training paradigm.
The main objective of this study was to determine the ability of children with ASD, including those who are minimally verbal, to perceive affective prosody. Secondarily, this study also sought to determine what relationships exist between the ability to perceive affective prosody and social responsiveness and/or nonverbal cognitive ability.
To date, 13 children with ASD (11 LFA, 2 HFA) and 21 neuro-typical (NT) children have completed the experimental task and two additional measures (nonverbal cognitive ability, social responsiveness deficits) for regression analyses. An innovative study design was developed that allowed minimally verbal LFA children to participate in and complete the experiment. First, low-pass filtered sentences were used to eliminate the confounding factors in linguistic stimuli that are associated with language abilities (e.g., knowledge of vocabulary, syntax), and to accommodate the heterogeneity within the autism spectrum. Second, a systematically scaffolded training paradigm was used to teach task expectations to all participants, supporting successful task completion.
ASD participants recognized prosodic conditions significantly less accurately than NT participants, and took significantly longer times to recognize all sentences compared to NT participants. The NT group required a significantly longer time to recognize affective prosody in shorter sentences compared to longer sentences, while the ASD group showed no such sentence length differences. Angry prosody was consistently the most difficult to recognize across groups. Nonverbal cognitive ability was a significant predictor for successful recognition of neutral and happy prosody; although low nonverbal cognitive skills do not preclude minimally verbal LFA children from correctly perceiving affective prosody.
This study demonstrated that it is possible for minimally verbal LFA children to successfully participate in experimental research using judgment tasks when provided with appropriate training, which is encouraging for translational purposes. Results pertinent to the HFA and minimally verbal LFA subgroups and the implications for intervention will be discussed.
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