Brief Report: Acoustic Evidence for Increased Articulatory Stability in the Speech of Adults with Autism Spectrum Disorder

Abstract

Subjective impressions of speech delivery in Autism Spectrum Disorder (ASD) as monotonic or over-precise are widespread but still lack robust acoustic evidence. This study provides a detailed acoustic characterization of the specificities of speech in individuals with ASD using an extensive sample of speech data, from the production of narratives and from spontaneous conversation. Syllable-level analyses (30,843 tokens in total) were performed on audio recordings from two sub-tasks of the Autism Diagnostic Observation Schedule from 20 adults with ASD and 20 pairwise matched neuro-typical adults, providing acoustic measures of fundamental frequency, jitter, shimmer and the first three formants. The results suggest that participants with ASD display a greater articulatory stability in vowel production than neuro-typical participants, both in phonation and articulatory gestures.

Phonetic Inflexibility in Autistic Adults

“…Such a hypothesis would be in line with models that associate ASD with an enhanced processing of low‐level, local properties of perceptual stimuli [Happé & Frith, 2006; Mottron, Dawson, Soulières, Hubert, & Burack, 2006; Pellicano & Burr, 2012], such as, for instance, superior pitch discrimination [Bonnel et al, 2010]. Another, not necessarily incompatible explanation is that the atypically high articulatory stability documented by Kissine and Geelhand [2019] in autistic individuals is limited to the sounds of their native tongue, and can thus be described as an atypically inflexible realization of the phonological repertoire. According to the first line of explanation, autistic speakers would display an enhanced control of a wide range of articulatory gestures; according to the latter they should be heavily constrained in the way they produce their native vowels.…”

“…Lack of robust supra‐segmental correlates of the atypical speech delivery in ASD may owe to the nature and the variety of tasks used to elicit verbal production, some of which autistic participants may find challenging for independent reasons [see Kissine & Geelhand, 2019, for a detailed discussion]: picture naming [Bonneh, Levanon, Dean‐Pardo, Lossos, & Adini, 2011; Nakai, Takashima, Takiguchi, & Takada, 2014], reading [Green & Tobin, 2009] or narrative retelling [Bone, Black, Ramakrishna, Grossman, & Narayanan, 2015; Diehl, Watson, Bennetto, McDonough, & Gunlogson, 2009; Filipe et al, 2014; Grossman et al, 2013]. However, it is also possible that more reliable group differences are located at segmental articulatory levels.…”

“…However, it is also possible that more reliable group differences are located at segmental articulatory levels. Kissine and Geelhand [2019] analyzed a large corpus of naturally produced speech and, based on the analysis of multiple acoustic characteristics, found that there was less variation in the production of different vowel types by autistic speakers relative to their neuro‐typical (NT) peers. This result suggests that subjective impressions of a monotonic, flat tone of voice in many verbal autistic speakers could partly be due to increased articulatory stability—or, equivalently, to a lack of phonetic flexibility—in the production of articulatory gestures.…”

“…Life‐long socio‐communicative deficits constitute a core characteristic of ASD, and it would be therefore natural to ask whether overly inflexible articulatory production in autism could be due to difficulties in adapting one's delivery style to a more informal register. Data analyzed by Kissine and Geelhand [2019] came from two ADOS [Lord et al, 2012] tasks: production of a narrative based on an illustrated book and semi‐structured conversation on the topic of solitude. The former task is more formal and gave rise to less variation in vowel productions than the latter—in both autistic and NT participants.…”

“…However, while more formal registers are associated with greater articulatory stability, autistic participants also exhibited significantly more stable vowels in both narrative production and semi‐structured conversation, that is, independently of the task register. Nonetheless, it remains possible that Kissine and Geelhand's [2019] autistic participants were overall adopting a more formal register, so that lower phonetic flexibility was due to a difficulty in switching to a more informal register rather than being a feature inherent in their speech production.…”