Identifying stable speech-language markers of autism in children: Preliminary evidence from a longitudinal telephony-based study (2022)

Abstract: This study examined differences in linguistic features produced by autistic and neurotypical (NT) children during brief picture descriptions, and assessed feature stability over time. Weekly speech samples from well-characterized participants were collected using a telephony system designed to improve access for geographically isolated and historically marginalized communities. Results showed stable group differences in certain acoustic features, some of which may potentially serve as key outcome measures in future treatment studies. These results highlight the importance of eliciting semi-structured speech samples in a variety of contexts over time, and adds to a growing body of research showing that fine-grained naturalistic communication features hold promise for intervention research.

## introduction natural sampling is a rich approach to investigating speech and language in autistic children. previous studies have shown that language behavior in autism differs from neurotypical (nt) patterns in a number of ways. for example, autistic children who are more severely impacted have been shown to produce less speech @xcite , slower speech @xcite , and speech with atypical voice quality compared to nt peers @xcite , including heightened jitter, increased jitter variability, but reduced harmonic-tonoise ratio @xcite . it has also been observed that autistic children's prosody differs from nt children, with qualitative observations ranging from "sing-songy" and exaggerated to monotonous, machine-like, or hollow @xcite @xcite @xcite . in the lexical domain, prior research has shown that autistic children use more nouns than nt peers when narrating a story from a picture, suggesting that the storytelling of children with autism is more objectfocused @xcite . also, children with autism use fewer filler words during clinical assessments than nt children @xcite , and they talk less about social topics during get-to-know-you conversations compared to nt children @xcite . it is also observed that children with autism have difficulties in using words in non-literal ways @xcite . research in this domain continues to emerge, but samples remain small and results occasionally conflict, as in the description of prosody being either "sing-songy" or monotonous, or fail to replicate (see @xcite for a meta-analysis of previous findings). prior studies of natural language in autism used a variety of data collection and analysis methods that could critically affect results and may have led to conflicting findings. for example, the presence of an unfamiliar adult during in-person or remote elicitations could adversely impact the behavior of autistic children, thus reducing the quality and informativeness of their language samples @xcite . also, children's linguistic behavior might differ depending on the specifics of the elicitation task in a given study, i.e., whether natural conversations or semi-structured speech tasks are used, and the characteristics of certain elicitation stimuli. in order to develop scalable, cost-effective, reliable intervention progress monitoring systems of autistic symptoms using speech as a primary target, it is necessary to understand how contextual and testing factors affect children's behavior. then, it will be possible to identify robust features that reliably index autism symptoms across heterogeneous testing conditions. toward this goal, we developed a telephony protocol to examine how various factors affect speech performance in autistic children and adolescents. telephony has particular potential to address service and monitoring gaps for autistic and nt children from historically marginalized and/or low-resource communities @xcite , and is a useful alternative to in-person data collection during the covid-19 pandemic. the final battery of our protocol consisted of seven versions of seven tasks that a parent or legal guardian could independently facilitate. in this preliminary report from an on-going study, we assessed children's speech and language features during one of the seven tasks (picture descriptions) collected in the first and second phone sessions. our goals were to (1) identify diagnostic group differences in automated speech and language features that are stable over time, and (2) examine potential effects of staff vs. parent administration in each diagnostic group. ## discussion in this study, we elicited picture descriptions from autistic and nt children using a telephony platform, and tested for the presence of diagnostic group differences in a variety of acoustic and lexical features over two sessions. results showed that autistic children produced greater local jitter, shimmer and the third and fourth orders of spectral moments, as well as shorter and less frequent pauses compared to nt children, across two sessions and with different stimuli. autistic children produced more speech during the second session when parents administered the task without study staff, compared to the first session. in contrast, nt children's speech duration did not differ by session. lexically, autistic children produced fewer conjunctions and pronouns than nt children, and used later-acquired content words compared to nt peers. our results also showed that autistic children used fewer seeor perception-related words and more time-related words than nt children. however, many other lexical features differed by session without significant group differences, suggesting that the picture stimuli may have had more influence than diagnostic group on lexical production. given that the acoustic features described here remained stable from the first to the second telephony session, and also distinguished diagnostic groups, they might hold potential as reliable speech markers of autism. higher jitter (variability in frequency) and shimmer (variability in amplitude) are perceived as harsh, hoarse, or breathy voice @xcite . the observation that autistic children's jitter and jitter variability were higher than nt peers is consistent with a previous study that also showed positive correlations between jitter and autism symptomology (ados scores; @xcite . yet, a recent meta-analysis study found that jitter was lower in autistic children than nt children in us and it did not differ in denmark, so future study is needed to resolve this mixed finding @xcite . also, previous studies showed consistently lower hnr values for autistic children compared to nt peers, with mixed findings in shimmer @xcite ; this differs from our pattern of results, where we found no difference in hnr but higher shimmer in children with autism. spectral moments in autism have rarely been studied, even though these measures are known to characterize individuals' voice timbre @xcite . we plan to study these features further in a larger sample after completing the data collection, to explore whether they could serve as validated speech markers of autism. children on the autism spectrum spoke longer and paused less frequently during the second session than the first session, whereas td children's duration measures did not differ by session. this finding is in line with prior research where fewer pauses were consistently observed in children with autism @xcite . this finding has at least two potential explanations: first, autistic individuals experience social-communicative challenges which might have hindered their willingness to speak freely in the presence of unfamiliar study staff. in this case, they may have spoken longer in the second session because their parent administered the task. thus, it is important to consider the presence or absence of study staff when interpreting studies of speech and language in autism. alternatively, children's greater speaking duration in the second session could simply be due to task familiarity; by week 2, children knew what to expect and had already completed the picture description once. finally, our study also found that autistic children produced fewer conjunctions, pronouns, seeand perception-related words with high aoa than nt children. we also observed that many wordlevel features differed by session in both the autistic and nt groups, suggesting that picture selection has an outsized effect on lexical features. in this study, we selected seven different pictures to prevent boredom and practice effects across multiple sessions. however, since different pictures include unique objects that children are likely to list in their descriptions, this will result in significant sessionbased differences in word-level features. picture selection and objects in pictures need to be carefully designed in future research, potentially with less weight placed on specific content words as stable outcome measures. as data collection continues in the current study, we will investigate whether group differences in more abstract lexical features (e.g., pronoun use) might remain stable over all seven sessions. ## conclusion telephony carries great potential as a low-cost and scalable platform for monitoring intervention responses from afar, as well as measuring longitudinal developmental changes in individual children. acoustic features extracted from data collected using a telephony system, which delivered consistent, high-quality recordings, could be important tools for identifying speech markers of autism.